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<ul>
<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">concurrent.futures</span></code> — Launching parallel tasks</a><ul>
<li><a class="reference internal" href="#executor-objects">Executor Objects</a></li>
<li><a class="reference internal" href="#threadpoolexecutor">ThreadPoolExecutor</a><ul>
<li><a class="reference internal" href="#threadpoolexecutor-example">ThreadPoolExecutor Example</a></li>
</ul>
</li>
<li><a class="reference internal" href="#interpreterpoolexecutor">InterpreterPoolExecutor</a></li>
<li><a class="reference internal" href="#processpoolexecutor">ProcessPoolExecutor</a><ul>
<li><a class="reference internal" href="#processpoolexecutor-example">ProcessPoolExecutor Example</a></li>
</ul>
</li>
<li><a class="reference internal" href="#future-objects">Future Objects</a></li>
<li><a class="reference internal" href="#module-functions">Module Functions</a></li>
<li><a class="reference internal" href="#exception-classes">Exception classes</a></li>
</ul>
</li>
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<p class="topless"><a href="concurrent.html"
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<section id="module-concurrent.futures">
<span id="concurrent-futures-launching-parallel-tasks"></span><h1><code class="xref py py-mod docutils literal notranslate"><span class="pre">concurrent.futures</span></code> — Launching parallel tasks<a class="headerlink" href="#module-concurrent.futures" title="Link to this heading">¶</a></h1>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.2.</span></p>
</div>
<p><strong>Source code:</strong> <a class="extlink-source reference external" href="https://github.com/python/cpython/tree/3.14/Lib/concurrent/futures/thread.py">Lib/concurrent/futures/thread.py</a>,
<a class="extlink-source reference external" href="https://github.com/python/cpython/tree/3.14/Lib/concurrent/futures/process.py">Lib/concurrent/futures/process.py</a>,
and <a class="extlink-source reference external" href="https://github.com/python/cpython/tree/3.14/Lib/concurrent/futures/interpreter.py">Lib/concurrent/futures/interpreter.py</a></p>
<hr class="docutils" />
<p>The <a class="reference internal" href="#module-concurrent.futures" title="concurrent.futures: Execute computations concurrently using threads or processes."><code class="xref py py-mod docutils literal notranslate"><span class="pre">concurrent.futures</span></code></a> module provides a high-level interface for
asynchronously executing callables.</p>
<p>The asynchronous execution can be performed with threads, using
<a class="reference internal" href="#concurrent.futures.ThreadPoolExecutor" title="concurrent.futures.ThreadPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">ThreadPoolExecutor</span></code></a> or <a class="reference internal" href="#concurrent.futures.InterpreterPoolExecutor" title="concurrent.futures.InterpreterPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">InterpreterPoolExecutor</span></code></a>,
or separate processes, using <a class="reference internal" href="#concurrent.futures.ProcessPoolExecutor" title="concurrent.futures.ProcessPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProcessPoolExecutor</span></code></a>.
Each implements the same interface, which is defined
by the abstract <a class="reference internal" href="#concurrent.futures.Executor" title="concurrent.futures.Executor"><code class="xref py py-class docutils literal notranslate"><span class="pre">Executor</span></code></a> class.</p>
<div class="availability docutils container">
<p><a class="reference internal" href="intro.html#availability"><span class="std std-ref">Availability</span></a>: not WASI.</p>
<p>This module does not work or is not available on WebAssembly. See
<a class="reference internal" href="intro.html#wasm-availability"><span class="std std-ref">WebAssembly platforms</span></a> for more information.</p>
</div>
<section id="executor-objects">
<h2>Executor Objects<a class="headerlink" href="#executor-objects" title="Link to this heading">¶</a></h2>
<dl class="py class">
<dt class="sig sig-object py" id="concurrent.futures.Executor">
<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">concurrent.futures.</span></span><span class="sig-name descname"><span class="pre">Executor</span></span><a class="headerlink" href="#concurrent.futures.Executor" title="Link to this definition">¶</a></dt>
<dd><p>An abstract class that provides methods to execute calls asynchronously. It
should not be used directly, but through its concrete subclasses.</p>
<dl class="py method">
<dt class="sig sig-object py" id="concurrent.futures.Executor.submit">
<span class="sig-name descname"><span class="pre">submit</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fn</span></span></em>, <em class="sig-param"><span class="positional-only-separator o"><abbr title="Positional-only parameter separator (PEP 570)"><span class="pre">/</span></abbr></span></em>, <em class="sig-param"><span class="o"><span class="pre">*</span></span><span class="n"><span class="pre">args</span></span></em>, <em class="sig-param"><span class="o"><span class="pre">**</span></span><span class="n"><span class="pre">kwargs</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#concurrent.futures.Executor.submit" title="Link to this definition">¶</a></dt>
<dd><p>Schedules the callable, <em>fn</em>, to be executed as <code class="docutils literal notranslate"><span class="pre">fn(*args,</span> <span class="pre">**kwargs)</span></code>
and returns a <a class="reference internal" href="#concurrent.futures.Future" title="concurrent.futures.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future</span></code></a> object representing the execution of the
callable.</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">with</span> <span class="n">ThreadPoolExecutor</span><span class="p">(</span><span class="n">max_workers</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span> <span class="k">as</span> <span class="n">executor</span><span class="p">:</span>
<span class="n">future</span> <span class="o">=</span> <span class="n">executor</span><span class="o">.</span><span class="n">submit</span><span class="p">(</span><span class="nb">pow</span><span class="p">,</span> <span class="mi">323</span><span class="p">,</span> <span class="mi">1235</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="n">future</span><span class="o">.</span><span class="n">result</span><span class="p">())</span>
</pre></div>
</div>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="concurrent.futures.Executor.map">
<span class="sig-name descname"><span class="pre">map</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fn</span></span></em>, <em class="sig-param"><span class="o"><span class="pre">*</span></span><span class="n"><span class="pre">iterables</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">timeout</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">chunksize</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">1</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">buffersize</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#concurrent.futures.Executor.map" title="Link to this definition">¶</a></dt>
<dd><p>Similar to <a class="reference internal" href="functions.html#map" title="map"><code class="xref py py-func docutils literal notranslate"><span class="pre">map(fn,</span> <span class="pre">*iterables)</span></code></a> except:</p>
<ul class="simple">
<li><p>The <em>iterables</em> are collected immediately rather than lazily, unless a
<em>buffersize</em> is specified to limit the number of submitted tasks whose
results have not yet been yielded. If the buffer is full, iteration over
the <em>iterables</em> pauses until a result is yielded from the buffer.</p></li>
<li><p><em>fn</em> is executed asynchronously and several calls to
<em>fn</em> may be made concurrently.</p></li>
</ul>
<p>The returned iterator raises a <a class="reference internal" href="exceptions.html#TimeoutError" title="TimeoutError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TimeoutError</span></code></a>
if <a class="reference internal" href="stdtypes.html#iterator.__next__" title="iterator.__next__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__next__()</span></code></a> is called and the result isn’t available
after <em>timeout</em> seconds from the original call to <a class="reference internal" href="#concurrent.futures.Executor.map" title="concurrent.futures.Executor.map"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Executor.map()</span></code></a>.
<em>timeout</em> can be an int or a float. If <em>timeout</em> is not specified or
<code class="docutils literal notranslate"><span class="pre">None</span></code>, there is no limit to the wait time.</p>
<p>If a <em>fn</em> call raises an exception, then that exception will be
raised when its value is retrieved from the iterator.</p>
<p>When using <a class="reference internal" href="#concurrent.futures.ProcessPoolExecutor" title="concurrent.futures.ProcessPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProcessPoolExecutor</span></code></a>, this method chops <em>iterables</em>
into a number of chunks which it submits to the pool as separate
tasks. The (approximate) size of these chunks can be specified by
setting <em>chunksize</em> to a positive integer. For very long iterables,
using a large value for <em>chunksize</em> can significantly improve
performance compared to the default size of 1. With
<a class="reference internal" href="#concurrent.futures.ThreadPoolExecutor" title="concurrent.futures.ThreadPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">ThreadPoolExecutor</span></code></a> and <a class="reference internal" href="#concurrent.futures.InterpreterPoolExecutor" title="concurrent.futures.InterpreterPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">InterpreterPoolExecutor</span></code></a>,
<em>chunksize</em> has no effect.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.5: </span>Added the <em>chunksize</em> parameter.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.14: </span>Added the <em>buffersize</em> parameter.</p>
</div>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="concurrent.futures.Executor.shutdown">
<span class="sig-name descname"><span class="pre">shutdown</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">wait</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">True</span></span></em>, <em class="sig-param"><span class="keyword-only-separator o"><abbr title="Keyword-only parameters separator (PEP 3102)"><span class="pre">*</span></abbr></span></em>, <em class="sig-param"><span class="n"><span class="pre">cancel_futures</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">False</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#concurrent.futures.Executor.shutdown" title="Link to this definition">¶</a></dt>
<dd><p>Signal the executor that it should free any resources that it is using
when the currently pending futures are done executing. Calls to
<a class="reference internal" href="#concurrent.futures.Executor.submit" title="concurrent.futures.Executor.submit"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Executor.submit()</span></code></a> and <a class="reference internal" href="#concurrent.futures.Executor.map" title="concurrent.futures.Executor.map"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Executor.map()</span></code></a> made after shutdown will
raise <a class="reference internal" href="exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">RuntimeError</span></code></a>.</p>
<p>If <em>wait</em> is <code class="docutils literal notranslate"><span class="pre">True</span></code> then this method will not return until all the
pending futures are done executing and the resources associated with the
executor have been freed. If <em>wait</em> is <code class="docutils literal notranslate"><span class="pre">False</span></code> then this method will
return immediately and the resources associated with the executor will be
freed when all pending futures are done executing. Regardless of the
value of <em>wait</em>, the entire Python program will not exit until all
pending futures are done executing.</p>
<p>If <em>cancel_futures</em> is <code class="docutils literal notranslate"><span class="pre">True</span></code>, this method will cancel all pending
futures that the executor has not started running. Any futures that
are completed or running won’t be cancelled, regardless of the value
of <em>cancel_futures</em>.</p>
<p>If both <em>cancel_futures</em> and <em>wait</em> are <code class="docutils literal notranslate"><span class="pre">True</span></code>, all futures that the
executor has started running will be completed prior to this method
returning. The remaining futures are cancelled.</p>
<p>You can avoid having to call this method explicitly if you use the executor
as a <a class="reference internal" href="../glossary.html#term-context-manager"><span class="xref std std-term">context manager</span></a> via the <a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a> statement, which
will shutdown the <a class="reference internal" href="#concurrent.futures.Executor" title="concurrent.futures.Executor"><code class="xref py py-class docutils literal notranslate"><span class="pre">Executor</span></code></a> (waiting as if <a class="reference internal" href="#concurrent.futures.Executor.shutdown" title="concurrent.futures.Executor.shutdown"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Executor.shutdown()</span></code></a>
were called with <em>wait</em> set to <code class="docutils literal notranslate"><span class="pre">True</span></code>):</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">shutil</span>
<span class="k">with</span> <span class="n">ThreadPoolExecutor</span><span class="p">(</span><span class="n">max_workers</span><span class="o">=</span><span class="mi">4</span><span class="p">)</span> <span class="k">as</span> <span class="n">e</span><span class="p">:</span>
<span class="n">e</span><span class="o">.</span><span class="n">submit</span><span class="p">(</span><span class="n">shutil</span><span class="o">.</span><span class="n">copy</span><span class="p">,</span> <span class="s1">'src1.txt'</span><span class="p">,</span> <span class="s1">'dest1.txt'</span><span class="p">)</span>
<span class="n">e</span><span class="o">.</span><span class="n">submit</span><span class="p">(</span><span class="n">shutil</span><span class="o">.</span><span class="n">copy</span><span class="p">,</span> <span class="s1">'src2.txt'</span><span class="p">,</span> <span class="s1">'dest2.txt'</span><span class="p">)</span>
<span class="n">e</span><span class="o">.</span><span class="n">submit</span><span class="p">(</span><span class="n">shutil</span><span class="o">.</span><span class="n">copy</span><span class="p">,</span> <span class="s1">'src3.txt'</span><span class="p">,</span> <span class="s1">'dest3.txt'</span><span class="p">)</span>
<span class="n">e</span><span class="o">.</span><span class="n">submit</span><span class="p">(</span><span class="n">shutil</span><span class="o">.</span><span class="n">copy</span><span class="p">,</span> <span class="s1">'src4.txt'</span><span class="p">,</span> <span class="s1">'dest4.txt'</span><span class="p">)</span>
</pre></div>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.9: </span>Added <em>cancel_futures</em>.</p>
</div>
</dd></dl>
</dd></dl>
</section>
<section id="threadpoolexecutor">
<h2>ThreadPoolExecutor<a class="headerlink" href="#threadpoolexecutor" title="Link to this heading">¶</a></h2>
<p><a class="reference internal" href="#concurrent.futures.ThreadPoolExecutor" title="concurrent.futures.ThreadPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">ThreadPoolExecutor</span></code></a> is an <a class="reference internal" href="#concurrent.futures.Executor" title="concurrent.futures.Executor"><code class="xref py py-class docutils literal notranslate"><span class="pre">Executor</span></code></a> subclass that uses a pool of
threads to execute calls asynchronously.</p>
<p>Deadlocks can occur when the callable associated with a <a class="reference internal" href="#concurrent.futures.Future" title="concurrent.futures.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future</span></code></a> waits on
the results of another <a class="reference internal" href="#concurrent.futures.Future" title="concurrent.futures.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future</span></code></a>. For example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">time</span>
<span class="k">def</span><span class="w"> </span><span class="nf">wait_on_b</span><span class="p">():</span>
<span class="n">time</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">5</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="n">b</span><span class="o">.</span><span class="n">result</span><span class="p">())</span> <span class="c1"># b will never complete because it is waiting on a.</span>
<span class="k">return</span> <span class="mi">5</span>
<span class="k">def</span><span class="w"> </span><span class="nf">wait_on_a</span><span class="p">():</span>
<span class="n">time</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">5</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="n">a</span><span class="o">.</span><span class="n">result</span><span class="p">())</span> <span class="c1"># a will never complete because it is waiting on b.</span>
<span class="k">return</span> <span class="mi">6</span>
<span class="n">executor</span> <span class="o">=</span> <span class="n">ThreadPoolExecutor</span><span class="p">(</span><span class="n">max_workers</span><span class="o">=</span><span class="mi">2</span><span class="p">)</span>
<span class="n">a</span> <span class="o">=</span> <span class="n">executor</span><span class="o">.</span><span class="n">submit</span><span class="p">(</span><span class="n">wait_on_b</span><span class="p">)</span>
<span class="n">b</span> <span class="o">=</span> <span class="n">executor</span><span class="o">.</span><span class="n">submit</span><span class="p">(</span><span class="n">wait_on_a</span><span class="p">)</span>
</pre></div>
</div>
<p>And:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span><span class="w"> </span><span class="nf">wait_on_future</span><span class="p">():</span>
<span class="n">f</span> <span class="o">=</span> <span class="n">executor</span><span class="o">.</span><span class="n">submit</span><span class="p">(</span><span class="nb">pow</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">2</span><span class="p">)</span>
<span class="c1"># This will never complete because there is only one worker thread and</span>
<span class="c1"># it is executing this function.</span>
<span class="nb">print</span><span class="p">(</span><span class="n">f</span><span class="o">.</span><span class="n">result</span><span class="p">())</span>
<span class="n">executor</span> <span class="o">=</span> <span class="n">ThreadPoolExecutor</span><span class="p">(</span><span class="n">max_workers</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span>
<span class="n">executor</span><span class="o">.</span><span class="n">submit</span><span class="p">(</span><span class="n">wait_on_future</span><span class="p">)</span>
</pre></div>
</div>
<dl class="py class">
<dt class="sig sig-object py" id="concurrent.futures.ThreadPoolExecutor">
<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">concurrent.futures.</span></span><span class="sig-name descname"><span class="pre">ThreadPoolExecutor</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">max_workers</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">thread_name_prefix</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">''</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">initializer</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">initargs</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">()</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#concurrent.futures.ThreadPoolExecutor" title="Link to this definition">¶</a></dt>
<dd><p>An <a class="reference internal" href="#concurrent.futures.Executor" title="concurrent.futures.Executor"><code class="xref py py-class docutils literal notranslate"><span class="pre">Executor</span></code></a> subclass that uses a pool of at most <em>max_workers</em>
threads to execute calls asynchronously.</p>
<p>All threads enqueued to <code class="docutils literal notranslate"><span class="pre">ThreadPoolExecutor</span></code> will be joined before the
interpreter can exit. Note that the exit handler which does this is
executed <em>before</em> any exit handlers added using <code class="docutils literal notranslate"><span class="pre">atexit</span></code>. This means
exceptions in the main thread must be caught and handled in order to
signal threads to exit gracefully. For this reason, it is recommended
that <code class="docutils literal notranslate"><span class="pre">ThreadPoolExecutor</span></code> not be used for long-running tasks.</p>
<p><em>initializer</em> is an optional callable that is called at the start of
each worker thread; <em>initargs</em> is a tuple of arguments passed to the
initializer. Should <em>initializer</em> raise an exception, all currently
pending jobs will raise a <a class="reference internal" href="#concurrent.futures.thread.BrokenThreadPool" title="concurrent.futures.thread.BrokenThreadPool"><code class="xref py py-exc docutils literal notranslate"><span class="pre">BrokenThreadPool</span></code></a>,
as well as any attempt to submit more jobs to the pool.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.5: </span>If <em>max_workers</em> is <code class="docutils literal notranslate"><span class="pre">None</span></code> or
not given, it will default to the number of processors on the machine,
multiplied by <code class="docutils literal notranslate"><span class="pre">5</span></code>, assuming that <a class="reference internal" href="#concurrent.futures.ThreadPoolExecutor" title="concurrent.futures.ThreadPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">ThreadPoolExecutor</span></code></a> is often
used to overlap I/O instead of CPU work and the number of workers
should be higher than the number of workers
for <a class="reference internal" href="#concurrent.futures.ProcessPoolExecutor" title="concurrent.futures.ProcessPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProcessPoolExecutor</span></code></a>.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.6: </span>Added the <em>thread_name_prefix</em> parameter to allow users to
control the <a class="reference internal" href="threading.html#threading.Thread" title="threading.Thread"><code class="xref py py-class docutils literal notranslate"><span class="pre">threading.Thread</span></code></a> names for worker threads created by
the pool for easier debugging.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.7: </span>Added the <em>initializer</em> and <em>initargs</em> arguments.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.8: </span>Default value of <em>max_workers</em> is changed to <code class="docutils literal notranslate"><span class="pre">min(32,</span> <span class="pre">os.cpu_count()</span> <span class="pre">+</span> <span class="pre">4)</span></code>.
This default value preserves at least 5 workers for I/O bound tasks.
It utilizes at most 32 CPU cores for CPU bound tasks which release the GIL.
And it avoids using very large resources implicitly on many-core machines.</p>
<p>ThreadPoolExecutor now reuses idle worker threads before starting
<em>max_workers</em> worker threads too.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.13: </span>Default value of <em>max_workers</em> is changed to
<code class="docutils literal notranslate"><span class="pre">min(32,</span> <span class="pre">(os.process_cpu_count()</span> <span class="pre">or</span> <span class="pre">1)</span> <span class="pre">+</span> <span class="pre">4)</span></code>.</p>
</div>
</dd></dl>
<section id="threadpoolexecutor-example">
<span id="id1"></span><h3>ThreadPoolExecutor Example<a class="headerlink" href="#threadpoolexecutor-example" title="Link to this heading">¶</a></h3>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">concurrent.futures</span>
<span class="kn">import</span><span class="w"> </span><span class="nn">urllib.request</span>
<span class="n">URLS</span> <span class="o">=</span> <span class="p">[</span><span class="s1">'http://www.foxnews.com/'</span><span class="p">,</span>
<span class="s1">'http://www.cnn.com/'</span><span class="p">,</span>
<span class="s1">'http://europe.wsj.com/'</span><span class="p">,</span>
<span class="s1">'http://www.bbc.co.uk/'</span><span class="p">,</span>
<span class="s1">'http://nonexistent-subdomain.python.org/'</span><span class="p">]</span>
<span class="c1"># Retrieve a single page and report the URL and contents</span>
<span class="k">def</span><span class="w"> </span><span class="nf">load_url</span><span class="p">(</span><span class="n">url</span><span class="p">,</span> <span class="n">timeout</span><span class="p">):</span>
<span class="k">with</span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">urlopen</span><span class="p">(</span><span class="n">url</span><span class="p">,</span> <span class="n">timeout</span><span class="o">=</span><span class="n">timeout</span><span class="p">)</span> <span class="k">as</span> <span class="n">conn</span><span class="p">:</span>
<span class="k">return</span> <span class="n">conn</span><span class="o">.</span><span class="n">read</span><span class="p">()</span>
<span class="c1"># We can use a with statement to ensure threads are cleaned up promptly</span>
<span class="k">with</span> <span class="n">concurrent</span><span class="o">.</span><span class="n">futures</span><span class="o">.</span><span class="n">ThreadPoolExecutor</span><span class="p">(</span><span class="n">max_workers</span><span class="o">=</span><span class="mi">5</span><span class="p">)</span> <span class="k">as</span> <span class="n">executor</span><span class="p">:</span>
<span class="c1"># Start the load operations and mark each future with its URL</span>
<span class="n">future_to_url</span> <span class="o">=</span> <span class="p">{</span><span class="n">executor</span><span class="o">.</span><span class="n">submit</span><span class="p">(</span><span class="n">load_url</span><span class="p">,</span> <span class="n">url</span><span class="p">,</span> <span class="mi">60</span><span class="p">):</span> <span class="n">url</span> <span class="k">for</span> <span class="n">url</span> <span class="ow">in</span> <span class="n">URLS</span><span class="p">}</span>
<span class="k">for</span> <span class="n">future</span> <span class="ow">in</span> <span class="n">concurrent</span><span class="o">.</span><span class="n">futures</span><span class="o">.</span><span class="n">as_completed</span><span class="p">(</span><span class="n">future_to_url</span><span class="p">):</span>
<span class="n">url</span> <span class="o">=</span> <span class="n">future_to_url</span><span class="p">[</span><span class="n">future</span><span class="p">]</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">data</span> <span class="o">=</span> <span class="n">future</span><span class="o">.</span><span class="n">result</span><span class="p">()</span>
<span class="k">except</span> <span class="ne">Exception</span> <span class="k">as</span> <span class="n">exc</span><span class="p">:</span>
<span class="nb">print</span><span class="p">(</span><span class="s1">'</span><span class="si">%r</span><span class="s1"> generated an exception: </span><span class="si">%s</span><span class="s1">'</span> <span class="o">%</span> <span class="p">(</span><span class="n">url</span><span class="p">,</span> <span class="n">exc</span><span class="p">))</span>
<span class="k">else</span><span class="p">:</span>
<span class="nb">print</span><span class="p">(</span><span class="s1">'</span><span class="si">%r</span><span class="s1"> page is </span><span class="si">%d</span><span class="s1"> bytes'</span> <span class="o">%</span> <span class="p">(</span><span class="n">url</span><span class="p">,</span> <span class="nb">len</span><span class="p">(</span><span class="n">data</span><span class="p">)))</span>
</pre></div>
</div>
</section>
</section>
<section id="interpreterpoolexecutor">
<h2>InterpreterPoolExecutor<a class="headerlink" href="#interpreterpoolexecutor" title="Link to this heading">¶</a></h2>
<p>The <a class="reference internal" href="#concurrent.futures.InterpreterPoolExecutor" title="concurrent.futures.InterpreterPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">InterpreterPoolExecutor</span></code></a> class uses a pool of interpreters
to execute calls asynchronously. It is a <a class="reference internal" href="#concurrent.futures.ThreadPoolExecutor" title="concurrent.futures.ThreadPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">ThreadPoolExecutor</span></code></a>
subclass, which means each worker is running in its own thread.
The difference here is that each worker has its own interpreter,
and runs each task using that interpreter.</p>
<p>The biggest benefit to using interpreters instead of only threads
is true multi-core parallelism. Each interpreter has its own
<a class="reference internal" href="../glossary.html#term-global-interpreter-lock"><span class="xref std std-term">Global Interpreter Lock</span></a>, so code
running in one interpreter can run on one CPU core, while code in
another interpreter runs unblocked on a different core.</p>
<p>The tradeoff is that writing concurrent code for use with multiple
interpreters can take extra effort. However, this is because it
forces you to be deliberate about how and when interpreters interact,
and to be explicit about what data is shared between interpreters.
This results in several benefits that help balance the extra effort,
including true multi-core parallelism, For example, code written
this way can make it easier to reason about concurrency. Another
major benefit is that you don’t have to deal with several of the
big pain points of using threads, like race conditions.</p>
<p>Each worker’s interpreter is isolated from all the other interpreters.
“Isolated” means each interpreter has its own runtime state and
operates completely independently. For example, if you redirect
<a class="reference internal" href="sys.html#sys.stdout" title="sys.stdout"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.stdout</span></code></a> in one interpreter, it will not be automatically
redirected to any other interpreter. If you import a module in one
interpreter, it is not automatically imported in any other. You
would need to import the module separately in interpreter where
you need it. In fact, each module imported in an interpreter is
a completely separate object from the same module in a different
interpreter, including <a class="reference internal" href="sys.html#module-sys" title="sys: Access system-specific parameters and functions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">sys</span></code></a>, <a class="reference internal" href="builtins.html#module-builtins" title="builtins: The module that provides the built-in namespace."><code class="xref py py-mod docutils literal notranslate"><span class="pre">builtins</span></code></a>,
and even <code class="docutils literal notranslate"><span class="pre">__main__</span></code>.</p>
<p>Isolation means a mutable object, or other data, cannot be used
by more than one interpreter at the same time. That effectively means
interpreters cannot actually share such objects or data. Instead,
each interpreter must have its own copy, and you will have to
synchronize any changes between the copies manually. Immutable
objects and data, like the builtin singletons, strings, and tuples
of immutable objects, don’t have these limitations.</p>
<p>Communicating and synchronizing between interpreters is most effectively
done using dedicated tools, like those proposed in <span class="target" id="index-0"></span><a class="pep reference external" href="https://peps.python.org/pep-0734/"><strong>PEP 734</strong></a>. One less
efficient alternative is to serialize with <a class="reference internal" href="pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pickle</span></code></a> and then send
the bytes over a shared <a class="reference internal" href="socket.html#module-socket" title="socket: Low-level networking interface."><code class="xref py py-mod docutils literal notranslate"><span class="pre">socket</span></code></a> or
<a class="reference internal" href="os.html#os.pipe" title="os.pipe"><code class="xref py py-func docutils literal notranslate"><span class="pre">pipe</span></code></a>.</p>
<dl class="py class">
<dt class="sig sig-object py" id="concurrent.futures.InterpreterPoolExecutor">
<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">concurrent.futures.</span></span><span class="sig-name descname"><span class="pre">InterpreterPoolExecutor</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">max_workers</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">thread_name_prefix</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">''</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">initializer</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">initargs</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">()</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#concurrent.futures.InterpreterPoolExecutor" title="Link to this definition">¶</a></dt>
<dd><p>A <a class="reference internal" href="#concurrent.futures.ThreadPoolExecutor" title="concurrent.futures.ThreadPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">ThreadPoolExecutor</span></code></a> subclass that executes calls asynchronously
using a pool of at most <em>max_workers</em> threads. Each thread runs
tasks in its own interpreter. The worker interpreters are isolated
from each other, which means each has its own runtime state and that
they can’t share any mutable objects or other data. Each interpreter
has its own <a class="reference internal" href="../glossary.html#term-global-interpreter-lock"><span class="xref std std-term">Global Interpreter Lock</span></a>,
which means code run with this executor has true multi-core parallelism.</p>
<p>The optional <em>initializer</em> and <em>initargs</em> arguments have the same
meaning as for <code class="xref py py-class docutils literal notranslate"><span class="pre">ThreadPoolExecutor</span></code>: the initializer is run
when each worker is created, though in this case it is run in
the worker’s interpreter. The executor serializes the <em>initializer</em>
and <em>initargs</em> using <a class="reference internal" href="pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pickle</span></code></a> when sending them to the worker’s
interpreter.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The executor may replace uncaught exceptions from <em>initializer</em>
with <a class="reference internal" href="#concurrent.futures.interpreter.ExecutionFailed" title="concurrent.futures.interpreter.ExecutionFailed"><code class="xref py py-class docutils literal notranslate"><span class="pre">ExecutionFailed</span></code></a>.</p>
</div>
<p>Other caveats from parent <a class="reference internal" href="#concurrent.futures.ThreadPoolExecutor" title="concurrent.futures.ThreadPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">ThreadPoolExecutor</span></code></a> apply here.</p>
</dd></dl>
<p><a class="reference internal" href="#concurrent.futures.Executor.submit" title="concurrent.futures.Executor.submit"><code class="xref py py-meth docutils literal notranslate"><span class="pre">submit()</span></code></a> and <a class="reference internal" href="#concurrent.futures.Executor.map" title="concurrent.futures.Executor.map"><code class="xref py py-meth docutils literal notranslate"><span class="pre">map()</span></code></a> work like normal,
except the worker serializes the callable and arguments using
<a class="reference internal" href="pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pickle</span></code></a> when sending them to its interpreter. The worker
likewise serializes the return value when sending it back.</p>
<p>When a worker’s current task raises an uncaught exception, the worker
always tries to preserve the exception as-is. If that is successful
then it also sets the <code class="docutils literal notranslate"><span class="pre">__cause__</span></code> to a corresponding
<a class="reference internal" href="#concurrent.futures.interpreter.ExecutionFailed" title="concurrent.futures.interpreter.ExecutionFailed"><code class="xref py py-class docutils literal notranslate"><span class="pre">ExecutionFailed</span></code></a>
instance, which contains a summary of the original exception.
In the uncommon case that the worker is not able to preserve the
original as-is then it directly preserves the corresponding
<a class="reference internal" href="#concurrent.futures.interpreter.ExecutionFailed" title="concurrent.futures.interpreter.ExecutionFailed"><code class="xref py py-class docutils literal notranslate"><span class="pre">ExecutionFailed</span></code></a>
instance instead.</p>
</section>
<section id="processpoolexecutor">
<h2>ProcessPoolExecutor<a class="headerlink" href="#processpoolexecutor" title="Link to this heading">¶</a></h2>
<p>The <a class="reference internal" href="#concurrent.futures.ProcessPoolExecutor" title="concurrent.futures.ProcessPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProcessPoolExecutor</span></code></a> class is an <a class="reference internal" href="#concurrent.futures.Executor" title="concurrent.futures.Executor"><code class="xref py py-class docutils literal notranslate"><span class="pre">Executor</span></code></a> subclass that
uses a pool of processes to execute calls asynchronously.
<a class="reference internal" href="#concurrent.futures.ProcessPoolExecutor" title="concurrent.futures.ProcessPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProcessPoolExecutor</span></code></a> uses the <a class="reference internal" href="multiprocessing.html#module-multiprocessing" title="multiprocessing: Process-based parallelism."><code class="xref py py-mod docutils literal notranslate"><span class="pre">multiprocessing</span></code></a> module, which
allows it to side-step the <a class="reference internal" href="../glossary.html#term-global-interpreter-lock"><span class="xref std std-term">Global Interpreter Lock</span></a> but also means that
only picklable objects can be executed and returned.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">__main__</span></code> module must be importable by worker subprocesses. This means
that <a class="reference internal" href="#concurrent.futures.ProcessPoolExecutor" title="concurrent.futures.ProcessPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProcessPoolExecutor</span></code></a> will not work in the interactive interpreter.</p>
<p>Calling <a class="reference internal" href="#concurrent.futures.Executor" title="concurrent.futures.Executor"><code class="xref py py-class docutils literal notranslate"><span class="pre">Executor</span></code></a> or <a class="reference internal" href="#concurrent.futures.Future" title="concurrent.futures.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future</span></code></a> methods from a callable submitted
to a <a class="reference internal" href="#concurrent.futures.ProcessPoolExecutor" title="concurrent.futures.ProcessPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProcessPoolExecutor</span></code></a> will result in deadlock.</p>
<p>Note that the restrictions on functions and arguments needing to picklable as
per <a class="reference internal" href="multiprocessing.html#multiprocessing.Process" title="multiprocessing.Process"><code class="xref py py-class docutils literal notranslate"><span class="pre">multiprocessing.Process</span></code></a> apply when using <a class="reference internal" href="#concurrent.futures.Executor.submit" title="concurrent.futures.Executor.submit"><code class="xref py py-meth docutils literal notranslate"><span class="pre">submit()</span></code></a>
and <a class="reference internal" href="#concurrent.futures.Executor.map" title="concurrent.futures.Executor.map"><code class="xref py py-meth docutils literal notranslate"><span class="pre">map()</span></code></a> on a <a class="reference internal" href="#concurrent.futures.ProcessPoolExecutor" title="concurrent.futures.ProcessPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProcessPoolExecutor</span></code></a>. A function defined
in a REPL or a lambda should not be expected to work.</p>
<dl class="py class">
<dt class="sig sig-object py" id="concurrent.futures.ProcessPoolExecutor">
<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">concurrent.futures.</span></span><span class="sig-name descname"><span class="pre">ProcessPoolExecutor</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">max_workers</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">mp_context</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">initializer</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">initargs</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">()</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">max_tasks_per_child</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#concurrent.futures.ProcessPoolExecutor" title="Link to this definition">¶</a></dt>
<dd><p>An <a class="reference internal" href="#concurrent.futures.Executor" title="concurrent.futures.Executor"><code class="xref py py-class docutils literal notranslate"><span class="pre">Executor</span></code></a> subclass that executes calls asynchronously using a pool
of at most <em>max_workers</em> processes. If <em>max_workers</em> is <code class="docutils literal notranslate"><span class="pre">None</span></code> or not
given, it will default to <a class="reference internal" href="os.html#os.process_cpu_count" title="os.process_cpu_count"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.process_cpu_count()</span></code></a>.
If <em>max_workers</em> is less than or equal to <code class="docutils literal notranslate"><span class="pre">0</span></code>, then a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a>
will be raised.
On Windows, <em>max_workers</em> must be less than or equal to <code class="docutils literal notranslate"><span class="pre">61</span></code>. If it is not
then <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> will be raised. If <em>max_workers</em> is <code class="docutils literal notranslate"><span class="pre">None</span></code>, then
the default chosen will be at most <code class="docutils literal notranslate"><span class="pre">61</span></code>, even if more processors are
available.
<em>mp_context</em> can be a <a class="reference internal" href="multiprocessing.html#module-multiprocessing" title="multiprocessing: Process-based parallelism."><code class="xref py py-mod docutils literal notranslate"><span class="pre">multiprocessing</span></code></a> context or <code class="docutils literal notranslate"><span class="pre">None</span></code>. It will be
used to launch the workers. If <em>mp_context</em> is <code class="docutils literal notranslate"><span class="pre">None</span></code> or not given, the
default <a class="reference internal" href="multiprocessing.html#module-multiprocessing" title="multiprocessing: Process-based parallelism."><code class="xref py py-mod docutils literal notranslate"><span class="pre">multiprocessing</span></code></a> context is used.
See <a class="reference internal" href="multiprocessing.html#multiprocessing-start-methods"><span class="std std-ref">Contexts and start methods</span></a>.</p>
<p><em>initializer</em> is an optional callable that is called at the start of
each worker process; <em>initargs</em> is a tuple of arguments passed to the
initializer. Should <em>initializer</em> raise an exception, all currently
pending jobs will raise a <a class="reference internal" href="#concurrent.futures.process.BrokenProcessPool" title="concurrent.futures.process.BrokenProcessPool"><code class="xref py py-exc docutils literal notranslate"><span class="pre">BrokenProcessPool</span></code></a>,
as well as any attempt to submit more jobs to the pool.</p>
<p><em>max_tasks_per_child</em> is an optional argument that specifies the maximum
number of tasks a single process can execute before it will exit and be
replaced with a fresh worker process. By default <em>max_tasks_per_child</em> is
<code class="docutils literal notranslate"><span class="pre">None</span></code> which means worker processes will live as long as the pool. When
a max is specified, the “spawn” multiprocessing start method will be used by
default in absence of a <em>mp_context</em> parameter. This feature is incompatible
with the “fork” start method.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.3: </span>When one of the worker processes terminates abruptly, a
<a class="reference internal" href="#concurrent.futures.process.BrokenProcessPool" title="concurrent.futures.process.BrokenProcessPool"><code class="xref py py-exc docutils literal notranslate"><span class="pre">BrokenProcessPool</span></code></a> error is now raised.
Previously, behaviour
was undefined but operations on the executor or its futures would often
freeze or deadlock.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.7: </span>The <em>mp_context</em> argument was added to allow users to control the
start_method for worker processes created by the pool.</p>
<p>Added the <em>initializer</em> and <em>initargs</em> arguments.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.11: </span>The <em>max_tasks_per_child</em> argument was added to allow users to
control the lifetime of workers in the pool.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.12: </span>On POSIX systems, if your application has multiple threads and the
<a class="reference internal" href="multiprocessing.html#module-multiprocessing" title="multiprocessing: Process-based parallelism."><code class="xref py py-mod docutils literal notranslate"><span class="pre">multiprocessing</span></code></a> context uses the <code class="docutils literal notranslate"><span class="pre">"fork"</span></code> start method:
The <a class="reference internal" href="os.html#os.fork" title="os.fork"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.fork()</span></code></a> function called internally to spawn workers may raise a
<a class="reference internal" href="exceptions.html#DeprecationWarning" title="DeprecationWarning"><code class="xref py py-exc docutils literal notranslate"><span class="pre">DeprecationWarning</span></code></a>. Pass a <em>mp_context</em> configured to use a
different start method. See the <a class="reference internal" href="os.html#os.fork" title="os.fork"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.fork()</span></code></a> documentation for
further explanation.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.13: </span><em>max_workers</em> uses <a class="reference internal" href="os.html#os.process_cpu_count" title="os.process_cpu_count"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.process_cpu_count()</span></code></a> by default, instead of
<a class="reference internal" href="os.html#os.cpu_count" title="os.cpu_count"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.cpu_count()</span></code></a>.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.14: </span>The default process start method (see
<a class="reference internal" href="multiprocessing.html#multiprocessing-start-methods"><span class="std std-ref">Contexts and start methods</span></a>) changed away from <em>fork</em>. If you
require the <em>fork</em> start method for <a class="reference internal" href="#concurrent.futures.ProcessPoolExecutor" title="concurrent.futures.ProcessPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProcessPoolExecutor</span></code></a> you must
explicitly pass <code class="docutils literal notranslate"><span class="pre">mp_context=multiprocessing.get_context("fork")</span></code>.</p>
</div>
<dl class="py method">
<dt class="sig sig-object py" id="concurrent.futures.ProcessPoolExecutor.terminate_workers">
<span class="sig-name descname"><span class="pre">terminate_workers</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#concurrent.futures.ProcessPoolExecutor.terminate_workers" title="Link to this definition">¶</a></dt>
<dd><p>Attempt to terminate all living worker processes immediately by calling
<a class="reference internal" href="multiprocessing.html#multiprocessing.Process.terminate" title="multiprocessing.Process.terminate"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Process.terminate</span></code></a> on each of them.
Internally, it will also call <a class="reference internal" href="#concurrent.futures.Executor.shutdown" title="concurrent.futures.Executor.shutdown"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Executor.shutdown()</span></code></a> to ensure that all
other resources associated with the executor are freed.</p>
<p>After calling this method the caller should no longer submit tasks to the
executor.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.14.</span></p>
</div>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="concurrent.futures.ProcessPoolExecutor.kill_workers">
<span class="sig-name descname"><span class="pre">kill_workers</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#concurrent.futures.ProcessPoolExecutor.kill_workers" title="Link to this definition">¶</a></dt>
<dd><p>Attempt to kill all living worker processes immediately by calling
<a class="reference internal" href="multiprocessing.html#multiprocessing.Process.kill" title="multiprocessing.Process.kill"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Process.kill</span></code></a> on each of them.
Internally, it will also call <a class="reference internal" href="#concurrent.futures.Executor.shutdown" title="concurrent.futures.Executor.shutdown"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Executor.shutdown()</span></code></a> to ensure that all
other resources associated with the executor are freed.</p>
<p>After calling this method the caller should no longer submit tasks to the
executor.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.14.</span></p>
</div>
</dd></dl>
</dd></dl>
<section id="processpoolexecutor-example">
<span id="id2"></span><h3>ProcessPoolExecutor Example<a class="headerlink" href="#processpoolexecutor-example" title="Link to this heading">¶</a></h3>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">concurrent.futures</span>
<span class="kn">import</span><span class="w"> </span><span class="nn">math</span>
<span class="n">PRIMES</span> <span class="o">=</span> <span class="p">[</span>
<span class="mi">112272535095293</span><span class="p">,</span>
<span class="mi">112582705942171</span><span class="p">,</span>
<span class="mi">112272535095293</span><span class="p">,</span>
<span class="mi">115280095190773</span><span class="p">,</span>
<span class="mi">115797848077099</span><span class="p">,</span>
<span class="mi">1099726899285419</span><span class="p">]</span>
<span class="k">def</span><span class="w"> </span><span class="nf">is_prime</span><span class="p">(</span><span class="n">n</span><span class="p">):</span>
<span class="k">if</span> <span class="n">n</span> <span class="o"><</span> <span class="mi">2</span><span class="p">:</span>
<span class="k">return</span> <span class="kc">False</span>
<span class="k">if</span> <span class="n">n</span> <span class="o">==</span> <span class="mi">2</span><span class="p">:</span>
<span class="k">return</span> <span class="kc">True</span>
<span class="k">if</span> <span class="n">n</span> <span class="o">%</span> <span class="mi">2</span> <span class="o">==</span> <span class="mi">0</span><span class="p">:</span>
<span class="k">return</span> <span class="kc">False</span>
<span class="n">sqrt_n</span> <span class="o">=</span> <span class="nb">int</span><span class="p">(</span><span class="n">math</span><span class="o">.</span><span class="n">floor</span><span class="p">(</span><span class="n">math</span><span class="o">.</span><span class="n">sqrt</span><span class="p">(</span><span class="n">n</span><span class="p">)))</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="n">sqrt_n</span> <span class="o">+</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">):</span>
<span class="k">if</span> <span class="n">n</span> <span class="o">%</span> <span class="n">i</span> <span class="o">==</span> <span class="mi">0</span><span class="p">:</span>
<span class="k">return</span> <span class="kc">False</span>
<span class="k">return</span> <span class="kc">True</span>
<span class="k">def</span><span class="w"> </span><span class="nf">main</span><span class="p">():</span>
<span class="k">with</span> <span class="n">concurrent</span><span class="o">.</span><span class="n">futures</span><span class="o">.</span><span class="n">ProcessPoolExecutor</span><span class="p">()</span> <span class="k">as</span> <span class="n">executor</span><span class="p">:</span>
<span class="k">for</span> <span class="n">number</span><span class="p">,</span> <span class="n">prime</span> <span class="ow">in</span> <span class="nb">zip</span><span class="p">(</span><span class="n">PRIMES</span><span class="p">,</span> <span class="n">executor</span><span class="o">.</span><span class="n">map</span><span class="p">(</span><span class="n">is_prime</span><span class="p">,</span> <span class="n">PRIMES</span><span class="p">)):</span>
<span class="nb">print</span><span class="p">(</span><span class="s1">'</span><span class="si">%d</span><span class="s1"> is prime: </span><span class="si">%s</span><span class="s1">'</span> <span class="o">%</span> <span class="p">(</span><span class="n">number</span><span class="p">,</span> <span class="n">prime</span><span class="p">))</span>
<span class="k">if</span> <span class="vm">__name__</span> <span class="o">==</span> <span class="s1">'__main__'</span><span class="p">:</span>
<span class="n">main</span><span class="p">()</span>
</pre></div>
</div>
</section>
</section>
<section id="future-objects">
<h2>Future Objects<a class="headerlink" href="#future-objects" title="Link to this heading">¶</a></h2>
<p>The <a class="reference internal" href="#concurrent.futures.Future" title="concurrent.futures.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future</span></code></a> class encapsulates the asynchronous execution of a callable.
<a class="reference internal" href="#concurrent.futures.Future" title="concurrent.futures.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future</span></code></a> instances are created by <a class="reference internal" href="#concurrent.futures.Executor.submit" title="concurrent.futures.Executor.submit"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Executor.submit()</span></code></a>.</p>
<dl class="py class">
<dt class="sig sig-object py" id="concurrent.futures.Future">
<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">concurrent.futures.</span></span><span class="sig-name descname"><span class="pre">Future</span></span><a class="headerlink" href="#concurrent.futures.Future" title="Link to this definition">¶</a></dt>
<dd><p>Encapsulates the asynchronous execution of a callable. <a class="reference internal" href="#concurrent.futures.Future" title="concurrent.futures.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future</span></code></a>
instances are created by <a class="reference internal" href="#concurrent.futures.Executor.submit" title="concurrent.futures.Executor.submit"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Executor.submit()</span></code></a> and should not be created
directly except for testing.</p>
<dl class="py method">
<dt class="sig sig-object py" id="concurrent.futures.Future.cancel">
<span class="sig-name descname"><span class="pre">cancel</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#concurrent.futures.Future.cancel" title="Link to this definition">¶</a></dt>
<dd><p>Attempt to cancel the call. If the call is currently being executed or
finished running and cannot be cancelled then the method will return
<code class="docutils literal notranslate"><span class="pre">False</span></code>, otherwise the call will be cancelled and the method will
return <code class="docutils literal notranslate"><span class="pre">True</span></code>.</p>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="concurrent.futures.Future.cancelled">
<span class="sig-name descname"><span class="pre">cancelled</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#concurrent.futures.Future.cancelled" title="Link to this definition">¶</a></dt>
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the call was successfully cancelled.</p>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="concurrent.futures.Future.running">
<span class="sig-name descname"><span class="pre">running</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#concurrent.futures.Future.running" title="Link to this definition">¶</a></dt>
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the call is currently being executed and cannot be
cancelled.</p>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="concurrent.futures.Future.done">
<span class="sig-name descname"><span class="pre">done</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#concurrent.futures.Future.done" title="Link to this definition">¶</a></dt>
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the call was successfully cancelled or finished
running.</p>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="concurrent.futures.Future.result">
<span class="sig-name descname"><span class="pre">result</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">timeout</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#concurrent.futures.Future.result" title="Link to this definition">¶</a></dt>
<dd><p>Return the value returned by the call. If the call hasn’t yet completed
then this method will wait up to <em>timeout</em> seconds. If the call hasn’t
completed in <em>timeout</em> seconds, then a
<a class="reference internal" href="exceptions.html#TimeoutError" title="TimeoutError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TimeoutError</span></code></a> will be raised. <em>timeout</em> can be
an int or float. If <em>timeout</em> is not specified or <code class="docutils literal notranslate"><span class="pre">None</span></code>, there is no
limit to the wait time.</p>
<p>If the future is cancelled before completing then <a class="reference internal" href="#concurrent.futures.CancelledError" title="concurrent.futures.CancelledError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">CancelledError</span></code></a>
will be raised.</p>
<p>If the call raised an exception, this method will raise the same exception.</p>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="concurrent.futures.Future.exception">
<span class="sig-name descname"><span class="pre">exception</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">timeout</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#concurrent.futures.Future.exception" title="Link to this definition">¶</a></dt>
<dd><p>Return the exception raised by the call. If the call hasn’t yet
completed then this method will wait up to <em>timeout</em> seconds. If the
call hasn’t completed in <em>timeout</em> seconds, then a
<a class="reference internal" href="exceptions.html#TimeoutError" title="TimeoutError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TimeoutError</span></code></a> will be raised. <em>timeout</em> can be
an int or float. If <em>timeout</em> is not specified or <code class="docutils literal notranslate"><span class="pre">None</span></code>, there is no
limit to the wait time.</p>
<p>If the future is cancelled before completing then <a class="reference internal" href="#concurrent.futures.CancelledError" title="concurrent.futures.CancelledError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">CancelledError</span></code></a>
will be raised.</p>
<p>If the call completed without raising, <code class="docutils literal notranslate"><span class="pre">None</span></code> is returned.</p>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="concurrent.futures.Future.add_done_callback">
<span class="sig-name descname"><span class="pre">add_done_callback</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fn</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#concurrent.futures.Future.add_done_callback" title="Link to this definition">¶</a></dt>
<dd><p>Attaches the callable <em>fn</em> to the future. <em>fn</em> will be called, with the
future as its only argument, when the future is cancelled or finishes
running.</p>
<p>Added callables are called in the order that they were added and are
always called in a thread belonging to the process that added them. If
the callable raises an <a class="reference internal" href="exceptions.html#Exception" title="Exception"><code class="xref py py-exc docutils literal notranslate"><span class="pre">Exception</span></code></a> subclass, it will be logged and
ignored. If the callable raises a <a class="reference internal" href="exceptions.html#BaseException" title="BaseException"><code class="xref py py-exc docutils literal notranslate"><span class="pre">BaseException</span></code></a> subclass, the
behavior is undefined.</p>
<p>If the future has already completed or been cancelled, <em>fn</em> will be
called immediately.</p>
</dd></dl>
<p>The following <a class="reference internal" href="#concurrent.futures.Future" title="concurrent.futures.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future</span></code></a> methods are meant for use in unit tests and
<a class="reference internal" href="#concurrent.futures.Executor" title="concurrent.futures.Executor"><code class="xref py py-class docutils literal notranslate"><span class="pre">Executor</span></code></a> implementations.</p>
<dl class="py method">
<dt class="sig sig-object py" id="concurrent.futures.Future.set_running_or_notify_cancel">
<span class="sig-name descname"><span class="pre">set_running_or_notify_cancel</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#concurrent.futures.Future.set_running_or_notify_cancel" title="Link to this definition">¶</a></dt>
<dd><p>This method should only be called by <a class="reference internal" href="#concurrent.futures.Executor" title="concurrent.futures.Executor"><code class="xref py py-class docutils literal notranslate"><span class="pre">Executor</span></code></a> implementations
before executing the work associated with the <a class="reference internal" href="#concurrent.futures.Future" title="concurrent.futures.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future</span></code></a> and by unit
tests.</p>
<p>If the method returns <code class="docutils literal notranslate"><span class="pre">False</span></code> then the <a class="reference internal" href="#concurrent.futures.Future" title="concurrent.futures.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future</span></code></a> was cancelled,
i.e. <a class="reference internal" href="#concurrent.futures.Future.cancel" title="concurrent.futures.Future.cancel"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Future.cancel()</span></code></a> was called and returned <code class="docutils literal notranslate"><span class="pre">True</span></code>. Any threads
waiting on the <a class="reference internal" href="#concurrent.futures.Future" title="concurrent.futures.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future</span></code></a> completing (i.e. through
<a class="reference internal" href="#concurrent.futures.as_completed" title="concurrent.futures.as_completed"><code class="xref py py-func docutils literal notranslate"><span class="pre">as_completed()</span></code></a> or <a class="reference internal" href="#concurrent.futures.wait" title="concurrent.futures.wait"><code class="xref py py-func docutils literal notranslate"><span class="pre">wait()</span></code></a>) will be woken up.</p>
<p>If the method returns <code class="docutils literal notranslate"><span class="pre">True</span></code> then the <a class="reference internal" href="#concurrent.futures.Future" title="concurrent.futures.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future</span></code></a> was not cancelled
and has been put in the running state, i.e. calls to
<a class="reference internal" href="#concurrent.futures.Future.running" title="concurrent.futures.Future.running"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Future.running()</span></code></a> will return <code class="docutils literal notranslate"><span class="pre">True</span></code>.</p>
<p>This method can only be called once and cannot be called after
<a class="reference internal" href="#concurrent.futures.Future.set_result" title="concurrent.futures.Future.set_result"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Future.set_result()</span></code></a> or <a class="reference internal" href="#concurrent.futures.Future.set_exception" title="concurrent.futures.Future.set_exception"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Future.set_exception()</span></code></a> have been
called.</p>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="concurrent.futures.Future.set_result">
<span class="sig-name descname"><span class="pre">set_result</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">result</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#concurrent.futures.Future.set_result" title="Link to this definition">¶</a></dt>
<dd><p>Sets the result of the work associated with the <a class="reference internal" href="#concurrent.futures.Future" title="concurrent.futures.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future</span></code></a> to
<em>result</em>.</p>
<p>This method should only be used by <a class="reference internal" href="#concurrent.futures.Executor" title="concurrent.futures.Executor"><code class="xref py py-class docutils literal notranslate"><span class="pre">Executor</span></code></a> implementations and
unit tests.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.8: </span>This method raises
<a class="reference internal" href="#concurrent.futures.InvalidStateError" title="concurrent.futures.InvalidStateError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">concurrent.futures.InvalidStateError</span></code></a> if the <a class="reference internal" href="#concurrent.futures.Future" title="concurrent.futures.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future</span></code></a> is
already done.</p>
</div>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="concurrent.futures.Future.set_exception">
<span class="sig-name descname"><span class="pre">set_exception</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">exception</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#concurrent.futures.Future.set_exception" title="Link to this definition">¶</a></dt>
<dd><p>Sets the result of the work associated with the <a class="reference internal" href="#concurrent.futures.Future" title="concurrent.futures.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future</span></code></a> to the
<a class="reference internal" href="exceptions.html#Exception" title="Exception"><code class="xref py py-class docutils literal notranslate"><span class="pre">Exception</span></code></a> <em>exception</em>.</p>
<p>This method should only be used by <a class="reference internal" href="#concurrent.futures.Executor" title="concurrent.futures.Executor"><code class="xref py py-class docutils literal notranslate"><span class="pre">Executor</span></code></a> implementations and
unit tests.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.8: </span>This method raises
<a class="reference internal" href="#concurrent.futures.InvalidStateError" title="concurrent.futures.InvalidStateError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">concurrent.futures.InvalidStateError</span></code></a> if the <a class="reference internal" href="#concurrent.futures.Future" title="concurrent.futures.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future</span></code></a> is
already done.</p>
</div>
</dd></dl>
</dd></dl>
</section>
<section id="module-functions">
<h2>Module Functions<a class="headerlink" href="#module-functions" title="Link to this heading">¶</a></h2>
<dl class="py function">
<dt class="sig sig-object py" id="concurrent.futures.wait">
<span class="sig-prename descclassname"><span class="pre">concurrent.futures.</span></span><span class="sig-name descname"><span class="pre">wait</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fs</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">timeout</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">return_when</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">ALL_COMPLETED</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#concurrent.futures.wait" title="Link to this definition">¶</a></dt>
<dd><p>Wait for the <a class="reference internal" href="#concurrent.futures.Future" title="concurrent.futures.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future</span></code></a> instances (possibly created by different
<a class="reference internal" href="#concurrent.futures.Executor" title="concurrent.futures.Executor"><code class="xref py py-class docutils literal notranslate"><span class="pre">Executor</span></code></a> instances) given by <em>fs</em> to complete. Duplicate futures
given to <em>fs</em> are removed and will be returned only once. Returns a named
2-tuple of sets. The first set, named <code class="docutils literal notranslate"><span class="pre">done</span></code>, contains the futures that
completed (finished or cancelled futures) before the wait completed. The
second set, named <code class="docutils literal notranslate"><span class="pre">not_done</span></code>, contains the futures that did not complete
(pending or running futures).</p>
<p><em>timeout</em> can be used to control the maximum number of seconds to wait before
returning. <em>timeout</em> can be an int or float. If <em>timeout</em> is not specified
or <code class="docutils literal notranslate"><span class="pre">None</span></code>, there is no limit to the wait time.</p>
<p><em>return_when</em> indicates when this function should return. It must be one of
the following constants:</p>
<table class="docutils align-default">
<thead>
<tr class="row-odd"><th class="head"><p>Constant</p></th>
<th class="head"><p>Description</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><dl class="py data">
<dt class="sig sig-object py" id="concurrent.futures.FIRST_COMPLETED">
<span class="sig-prename descclassname"><span class="pre">concurrent.futures.</span></span><span class="sig-name descname"><span class="pre">FIRST_COMPLETED</span></span><a class="headerlink" href="#concurrent.futures.FIRST_COMPLETED" title="Link to this definition">¶</a></dt>
<dd></dd></dl>
</td>
<td><p>The function will return when any future finishes or is cancelled.</p></td>
</tr>
<tr class="row-odd"><td><dl class="py data">
<dt class="sig sig-object py" id="concurrent.futures.FIRST_EXCEPTION">
<span class="sig-prename descclassname"><span class="pre">concurrent.futures.</span></span><span class="sig-name descname"><span class="pre">FIRST_EXCEPTION</span></span><a class="headerlink" href="#concurrent.futures.FIRST_EXCEPTION" title="Link to this definition">¶</a></dt>
<dd></dd></dl>
</td>
<td><p>The function will return when any future finishes by raising an
exception. If no future raises an exception
then it is equivalent to <a class="reference internal" href="#concurrent.futures.ALL_COMPLETED" title="concurrent.futures.ALL_COMPLETED"><code class="xref py py-const docutils literal notranslate"><span class="pre">ALL_COMPLETED</span></code></a>.</p></td>
</tr>
<tr class="row-even"><td><dl class="py data">
<dt class="sig sig-object py" id="concurrent.futures.ALL_COMPLETED">
<span class="sig-prename descclassname"><span class="pre">concurrent.futures.</span></span><span class="sig-name descname"><span class="pre">ALL_COMPLETED</span></span><a class="headerlink" href="#concurrent.futures.ALL_COMPLETED" title="Link to this definition">¶</a></dt>
<dd></dd></dl>
</td>
<td><p>The function will return when all futures finish or are cancelled.</p></td>
</tr>
</tbody>
</table>
</dd></dl>
<dl class="py function">
<dt class="sig sig-object py" id="concurrent.futures.as_completed">
<span class="sig-prename descclassname"><span class="pre">concurrent.futures.</span></span><span class="sig-name descname"><span class="pre">as_completed</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fs</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">timeout</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#concurrent.futures.as_completed" title="Link to this definition">¶</a></dt>
<dd><p>Returns an iterator over the <a class="reference internal" href="#concurrent.futures.Future" title="concurrent.futures.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future</span></code></a> instances (possibly created by
different <a class="reference internal" href="#concurrent.futures.Executor" title="concurrent.futures.Executor"><code class="xref py py-class docutils literal notranslate"><span class="pre">Executor</span></code></a> instances) given by <em>fs</em> that yields futures as
they complete (finished or cancelled futures). Any futures given by <em>fs</em> that
are duplicated will be returned once. Any futures that completed before
<a class="reference internal" href="#concurrent.futures.as_completed" title="concurrent.futures.as_completed"><code class="xref py py-func docutils literal notranslate"><span class="pre">as_completed()</span></code></a> is called will be yielded first. The returned iterator
raises a <a class="reference internal" href="exceptions.html#TimeoutError" title="TimeoutError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TimeoutError</span></code></a> if <a class="reference internal" href="stdtypes.html#iterator.__next__" title="iterator.__next__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__next__()</span></code></a>
is called and the result isn’t available after <em>timeout</em> seconds from the
original call to <a class="reference internal" href="#concurrent.futures.as_completed" title="concurrent.futures.as_completed"><code class="xref py py-func docutils literal notranslate"><span class="pre">as_completed()</span></code></a>. <em>timeout</em> can be an int or float. If
<em>timeout</em> is not specified or <code class="docutils literal notranslate"><span class="pre">None</span></code>, there is no limit to the wait time.</p>
</dd></dl>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<dl class="simple">
<dt><span class="target" id="index-1"></span><a class="pep reference external" href="https://peps.python.org/pep-3148/"><strong>PEP 3148</strong></a> – futures - execute computations asynchronously</dt><dd><p>The proposal which described this feature for inclusion in the Python
standard library.</p>
</dd>
</dl>
</div>
</section>
<section id="exception-classes">
<h2>Exception classes<a class="headerlink" href="#exception-classes" title="Link to this heading">¶</a></h2>
<dl class="py exception">
<dt class="sig sig-object py" id="concurrent.futures.CancelledError">
<em class="property"><span class="k"><span class="pre">exception</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">concurrent.futures.</span></span><span class="sig-name descname"><span class="pre">CancelledError</span></span><a class="headerlink" href="#concurrent.futures.CancelledError" title="Link to this definition">¶</a></dt>
<dd><p>Raised when a future is cancelled.</p>
</dd></dl>
<dl class="py exception">
<dt class="sig sig-object py" id="concurrent.futures.TimeoutError">
<em class="property"><span class="k"><span class="pre">exception</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">concurrent.futures.</span></span><span class="sig-name descname"><span class="pre">TimeoutError</span></span><a class="headerlink" href="#concurrent.futures.TimeoutError" title="Link to this definition">¶</a></dt>
<dd><p>A deprecated alias of <a class="reference internal" href="exceptions.html#TimeoutError" title="TimeoutError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TimeoutError</span></code></a>,
raised when a future operation exceeds the given timeout.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.11: </span>This class was made an alias of <a class="reference internal" href="exceptions.html#TimeoutError" title="TimeoutError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TimeoutError</span></code></a>.</p>
</div>
</dd></dl>
<dl class="py exception">
<dt class="sig sig-object py" id="concurrent.futures.BrokenExecutor">
<em class="property"><span class="k"><span class="pre">exception</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">concurrent.futures.</span></span><span class="sig-name descname"><span class="pre">BrokenExecutor</span></span><a class="headerlink" href="#concurrent.futures.BrokenExecutor" title="Link to this definition">¶</a></dt>
<dd><p>Derived from <a class="reference internal" href="exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">RuntimeError</span></code></a>, this exception class is raised
when an executor is broken for some reason, and cannot be used
to submit or execute new tasks.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.7.</span></p>
</div>
</dd></dl>
<dl class="py exception">
<dt class="sig sig-object py" id="concurrent.futures.InvalidStateError">
<em class="property"><span class="k"><span class="pre">exception</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">concurrent.futures.</span></span><span class="sig-name descname"><span class="pre">InvalidStateError</span></span><a class="headerlink" href="#concurrent.futures.InvalidStateError" title="Link to this definition">¶</a></dt>
<dd><p>Raised when an operation is performed on a future that is not allowed
in the current state.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.8.</span></p>
</div>
</dd></dl>
<dl class="py exception">
<dt class="sig sig-object py" id="concurrent.futures.thread.BrokenThreadPool">
<em class="property"><span class="k"><span class="pre">exception</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">concurrent.futures.thread.</span></span><span class="sig-name descname"><span class="pre">BrokenThreadPool</span></span><a class="headerlink" href="#concurrent.futures.thread.BrokenThreadPool" title="Link to this definition">¶</a></dt>
<dd><p>Derived from <a class="reference internal" href="#concurrent.futures.BrokenExecutor" title="concurrent.futures.BrokenExecutor"><code class="xref py py-exc docutils literal notranslate"><span class="pre">BrokenExecutor</span></code></a>, this exception
class is raised when one of the workers
of a <a class="reference internal" href="#concurrent.futures.ThreadPoolExecutor" title="concurrent.futures.ThreadPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">ThreadPoolExecutor</span></code></a>
has failed initializing.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.7.</span></p>
</div>
</dd></dl>
<dl class="py exception">
<dt class="sig sig-object py" id="concurrent.futures.interpreter.BrokenInterpreterPool">
<em class="property"><span class="k"><span class="pre">exception</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">concurrent.futures.interpreter.</span></span><span class="sig-name descname"><span class="pre">BrokenInterpreterPool</span></span><a class="headerlink" href="#concurrent.futures.interpreter.BrokenInterpreterPool" title="Link to this definition">¶</a></dt>
<dd><p>Derived from <a class="reference internal" href="#concurrent.futures.thread.BrokenThreadPool" title="concurrent.futures.thread.BrokenThreadPool"><code class="xref py py-exc docutils literal notranslate"><span class="pre">BrokenThreadPool</span></code></a>,
this exception class is raised when one of the workers
of a <a class="reference internal" href="#concurrent.futures.InterpreterPoolExecutor" title="concurrent.futures.InterpreterPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">InterpreterPoolExecutor</span></code></a>
has failed initializing.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.14.</span></p>
</div>
</dd></dl>
<dl class="py exception">
<dt class="sig sig-object py" id="concurrent.futures.interpreter.ExecutionFailed">
<em class="property"><span class="k"><span class="pre">exception</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">concurrent.futures.interpreter.</span></span><span class="sig-name descname"><span class="pre">ExecutionFailed</span></span><a class="headerlink" href="#concurrent.futures.interpreter.ExecutionFailed" title="Link to this definition">¶</a></dt>
<dd><p>Raised from <a class="reference internal" href="#concurrent.futures.InterpreterPoolExecutor" title="concurrent.futures.InterpreterPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">InterpreterPoolExecutor</span></code></a> when
the given initializer fails or from
<a class="reference internal" href="#concurrent.futures.Executor.submit" title="concurrent.futures.Executor.submit"><code class="xref py py-meth docutils literal notranslate"><span class="pre">submit()</span></code></a> when there’s an uncaught
exception from the submitted task.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.14.</span></p>
</div>
</dd></dl>
<dl class="py exception">
<dt class="sig sig-object py" id="concurrent.futures.process.BrokenProcessPool">
<em class="property"><span class="k"><span class="pre">exception</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">concurrent.futures.process.</span></span><span class="sig-name descname"><span class="pre">BrokenProcessPool</span></span><a class="headerlink" href="#concurrent.futures.process.BrokenProcessPool" title="Link to this definition">¶</a></dt>
<dd><p>Derived from <a class="reference internal" href="#concurrent.futures.BrokenExecutor" title="concurrent.futures.BrokenExecutor"><code class="xref py py-exc docutils literal notranslate"><span class="pre">BrokenExecutor</span></code></a> (formerly
<a class="reference internal" href="exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">RuntimeError</span></code></a>), this exception class is raised when one of the
workers of a <a class="reference internal" href="#concurrent.futures.ProcessPoolExecutor" title="concurrent.futures.ProcessPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProcessPoolExecutor</span></code></a>
has terminated in a non-clean
fashion (for example, if it was killed from the outside).</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.3.</span></p>
</div>
</dd></dl>
</section>
</section>
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<h3><a href="../contents.html">Table of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">concurrent.futures</span></code> — Launching parallel tasks</a><ul>
<li><a class="reference internal" href="#executor-objects">Executor Objects</a></li>
<li><a class="reference internal" href="#threadpoolexecutor">ThreadPoolExecutor</a><ul>
<li><a class="reference internal" href="#threadpoolexecutor-example">ThreadPoolExecutor Example</a></li>
</ul>
</li>
<li><a class="reference internal" href="#interpreterpoolexecutor">InterpreterPoolExecutor</a></li>
<li><a class="reference internal" href="#processpoolexecutor">ProcessPoolExecutor</a><ul>
<li><a class="reference internal" href="#processpoolexecutor-example">ProcessPoolExecutor Example</a></li>
</ul>
</li>
<li><a class="reference internal" href="#future-objects">Future Objects</a></li>
<li><a class="reference internal" href="#module-functions">Module Functions</a></li>
<li><a class="reference internal" href="#exception-classes">Exception classes</a></li>
</ul>
</li>
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