path: root/devdocs/python~3.12/library%2Fconcurrency.html

 <span id="concurrency"></span><h1>Concurrent Execution</h1> <p>The modules described in this chapter provide support for concurrent execution of code. The appropriate choice of tool will depend on the task to be executed (CPU bound vs IO bound) and preferred style of development (event driven cooperative multitasking vs preemptive multitasking). Here’s an overview:</p>  <ul> <li class="toctree-l1">
<a class="reference internal" href="threading"><code>threading</code> — Thread-based parallelism</a><ul> <li class="toctree-l2"><a class="reference internal" href="threading#thread-local-data">Thread-Local Data</a></li> <li class="toctree-l2"><a class="reference internal" href="threading#thread-objects">Thread Objects</a></li> <li class="toctree-l2"><a class="reference internal" href="threading#lock-objects">Lock Objects</a></li> <li class="toctree-l2"><a class="reference internal" href="threading#rlock-objects">RLock Objects</a></li> <li class="toctree-l2"><a class="reference internal" href="threading#condition-objects">Condition Objects</a></li> <li class="toctree-l2">
<a class="reference internal" href="threading#semaphore-objects">Semaphore Objects</a><ul> <li class="toctree-l3"><a class="reference internal" href="threading#semaphore-example"><code>Semaphore</code> Example</a></li> </ul> </li> <li class="toctree-l2"><a class="reference internal" href="threading#event-objects">Event Objects</a></li> <li class="toctree-l2"><a class="reference internal" href="threading#timer-objects">Timer Objects</a></li> <li class="toctree-l2"><a class="reference internal" href="threading#barrier-objects">Barrier Objects</a></li> <li class="toctree-l2"><a class="reference internal" href="threading#using-locks-conditions-and-semaphores-in-the-with-statement">Using locks, conditions, and semaphores in the <code>with</code> statement</a></li> </ul> </li> <li class="toctree-l1">
<a class="reference internal" href="multiprocessing"><code>multiprocessing</code> — Process-based parallelism</a><ul> <li class="toctree-l2">
<a class="reference internal" href="multiprocessing#introduction">Introduction</a><ul> <li class="toctree-l3"><a class="reference internal" href="multiprocessing#the-process-class">The <code>Process</code> class</a></li> <li class="toctree-l3"><a class="reference internal" href="multiprocessing#contexts-and-start-methods">Contexts and start methods</a></li> <li class="toctree-l3"><a class="reference internal" href="multiprocessing#exchanging-objects-between-processes">Exchanging objects between processes</a></li> <li class="toctree-l3"><a class="reference internal" href="multiprocessing#synchronization-between-processes">Synchronization between processes</a></li> <li class="toctree-l3"><a class="reference internal" href="multiprocessing#sharing-state-between-processes">Sharing state between processes</a></li> <li class="toctree-l3"><a class="reference internal" href="multiprocessing#using-a-pool-of-workers">Using a pool of workers</a></li> </ul> </li> <li class="toctree-l2">
<a class="reference internal" href="multiprocessing#reference">Reference</a><ul> <li class="toctree-l3"><a class="reference internal" href="multiprocessing#process-and-exceptions"><code>Process</code> and exceptions</a></li> <li class="toctree-l3"><a class="reference internal" href="multiprocessing#pipes-and-queues">Pipes and Queues</a></li> <li class="toctree-l3"><a class="reference internal" href="multiprocessing#miscellaneous">Miscellaneous</a></li> <li class="toctree-l3"><a class="reference internal" href="multiprocessing#connection-objects">Connection Objects</a></li> <li class="toctree-l3"><a class="reference internal" href="multiprocessing#synchronization-primitives">Synchronization primitives</a></li> <li class="toctree-l3">
<a class="reference internal" href="multiprocessing#shared-ctypes-objects">Shared <code>ctypes</code> Objects</a><ul> <li class="toctree-l4"><a class="reference internal" href="multiprocessing#module-multiprocessing.sharedctypes">The <code>multiprocessing.sharedctypes</code> module</a></li> </ul> </li> <li class="toctree-l3">
<a class="reference internal" href="multiprocessing#managers">Managers</a><ul> <li class="toctree-l4"><a class="reference internal" href="multiprocessing#customized-managers">Customized managers</a></li> <li class="toctree-l4"><a class="reference internal" href="multiprocessing#using-a-remote-manager">Using a remote manager</a></li> </ul> </li> <li class="toctree-l3">
<a class="reference internal" href="multiprocessing#proxy-objects">Proxy Objects</a><ul> <li class="toctree-l4"><a class="reference internal" href="multiprocessing#cleanup">Cleanup</a></li> </ul> </li> <li class="toctree-l3"><a class="reference internal" href="multiprocessing#module-multiprocessing.pool">Process Pools</a></li> <li class="toctree-l3">
<a class="reference internal" href="multiprocessing#module-multiprocessing.connection">Listeners and Clients</a><ul> <li class="toctree-l4"><a class="reference internal" href="multiprocessing#address-formats">Address Formats</a></li> </ul> </li> <li class="toctree-l3"><a class="reference internal" href="multiprocessing#authentication-keys">Authentication keys</a></li> <li class="toctree-l3"><a class="reference internal" href="multiprocessing#logging">Logging</a></li> <li class="toctree-l3"><a class="reference internal" href="multiprocessing#module-multiprocessing.dummy">The <code>multiprocessing.dummy</code> module</a></li> </ul> </li> <li class="toctree-l2">
<a class="reference internal" href="multiprocessing#programming-guidelines">Programming guidelines</a><ul> <li class="toctree-l3"><a class="reference internal" href="multiprocessing#all-start-methods">All start methods</a></li> <li class="toctree-l3"><a class="reference internal" href="multiprocessing#the-spawn-and-forkserver-start-methods">The spawn and forkserver start methods</a></li> </ul> </li> <li class="toctree-l2"><a class="reference internal" href="multiprocessing#examples">Examples</a></li> </ul> </li> <li class="toctree-l1"><a class="reference internal" href="multiprocessing.shared_memory"><code>multiprocessing.shared_memory</code> — Shared memory for direct access across processes</a></li> <li class="toctree-l1"><a class="reference internal" href="concurrent">The <code>concurrent</code> package</a></li> <li class="toctree-l1">
<a class="reference internal" href="concurrent.futures"><code>concurrent.futures</code> — Launching parallel tasks</a><ul> <li class="toctree-l2"><a class="reference internal" href="concurrent.futures#executor-objects">Executor Objects</a></li> <li class="toctree-l2">
<a class="reference internal" href="concurrent.futures#threadpoolexecutor">ThreadPoolExecutor</a><ul> <li class="toctree-l3"><a class="reference internal" href="concurrent.futures#threadpoolexecutor-example">ThreadPoolExecutor Example</a></li> </ul> </li> <li class="toctree-l2">
<a class="reference internal" href="concurrent.futures#processpoolexecutor">ProcessPoolExecutor</a><ul> <li class="toctree-l3"><a class="reference internal" href="concurrent.futures#processpoolexecutor-example">ProcessPoolExecutor Example</a></li> </ul> </li> <li class="toctree-l2"><a class="reference internal" href="concurrent.futures#future-objects">Future Objects</a></li> <li class="toctree-l2"><a class="reference internal" href="concurrent.futures#module-functions">Module Functions</a></li> <li class="toctree-l2"><a class="reference internal" href="concurrent.futures#exception-classes">Exception classes</a></li> </ul> </li> <li class="toctree-l1">
<a class="reference internal" href="subprocess"><code>subprocess</code> — Subprocess management</a><ul> <li class="toctree-l2">
<a class="reference internal" href="subprocess#using-the-subprocess-module">Using the <code>subprocess</code> Module</a><ul> <li class="toctree-l3"><a class="reference internal" href="subprocess#frequently-used-arguments">Frequently Used Arguments</a></li> <li class="toctree-l3"><a class="reference internal" href="subprocess#popen-constructor">Popen Constructor</a></li> <li class="toctree-l3"><a class="reference internal" href="subprocess#exceptions">Exceptions</a></li> </ul> </li> <li class="toctree-l2"><a class="reference internal" href="subprocess#security-considerations">Security Considerations</a></li> <li class="toctree-l2"><a class="reference internal" href="subprocess#popen-objects">Popen Objects</a></li> <li class="toctree-l2">
<a class="reference internal" href="subprocess#windows-popen-helpers">Windows Popen Helpers</a><ul> <li class="toctree-l3"><a class="reference internal" href="subprocess#windows-constants">Windows Constants</a></li> </ul> </li> <li class="toctree-l2"><a class="reference internal" href="subprocess#older-high-level-api">Older high-level API</a></li> <li class="toctree-l2">
<a class="reference internal" href="subprocess#replacing-older-functions-with-the-subprocess-module">Replacing Older Functions with the <code>subprocess</code> Module</a><ul> <li class="toctree-l3"><a class="reference internal" href="subprocess#replacing-bin-sh-shell-command-substitution">Replacing <strong class="program">/bin/sh</strong> shell command substitution</a></li> <li class="toctree-l3"><a class="reference internal" href="subprocess#replacing-shell-pipeline">Replacing shell pipeline</a></li> <li class="toctree-l3"><a class="reference internal" href="subprocess#replacing-os-system">Replacing <code>os.system()</code></a></li> <li class="toctree-l3"><a class="reference internal" href="subprocess#replacing-the-os-spawn-family">Replacing the <code>os.spawn</code> family</a></li> <li class="toctree-l3"><a class="reference internal" href="subprocess#replacing-os-popen-os-popen2-os-popen3">Replacing <code>os.popen()</code>, <code>os.popen2()</code>, <code>os.popen3()</code></a></li> <li class="toctree-l3"><a class="reference internal" href="subprocess#replacing-functions-from-the-popen2-module">Replacing functions from the <code>popen2</code> module</a></li> </ul> </li> <li class="toctree-l2"><a class="reference internal" href="subprocess#legacy-shell-invocation-functions">Legacy Shell Invocation Functions</a></li> <li class="toctree-l2">
<a class="reference internal" href="subprocess#notes">Notes</a><ul> <li class="toctree-l3"><a class="reference internal" href="subprocess#converting-an-argument-sequence-to-a-string-on-windows">Converting an argument sequence to a string on Windows</a></li> <li class="toctree-l3"><a class="reference internal" href="subprocess#disabling-use-of-vfork-or-posix-spawn">Disabling use of <code>vfork()</code> or <code>posix_spawn()</code></a></li> </ul> </li> </ul> </li> <li class="toctree-l1">
<a class="reference internal" href="sched"><code>sched</code> — Event scheduler</a><ul> <li class="toctree-l2"><a class="reference internal" href="sched#scheduler-objects">Scheduler Objects</a></li> </ul> </li> <li class="toctree-l1">
<a class="reference internal" href="queue"><code>queue</code> — A synchronized queue class</a><ul> <li class="toctree-l2"><a class="reference internal" href="queue#queue-objects">Queue Objects</a></li> <li class="toctree-l2"><a class="reference internal" href="queue#simplequeue-objects">SimpleQueue Objects</a></li> </ul> </li> <li class="toctree-l1">
<a class="reference internal" href="contextvars"><code>contextvars</code> — Context Variables</a><ul> <li class="toctree-l2"><a class="reference internal" href="contextvars#context-variables">Context Variables</a></li> <li class="toctree-l2"><a class="reference internal" href="contextvars#manual-context-management">Manual Context Management</a></li> <li class="toctree-l2"><a class="reference internal" href="contextvars#asyncio-support">asyncio support</a></li> </ul> </li> </ul>  <p>The following are support modules for some of the above services:</p>  <ul> <li class="toctree-l1"><a class="reference internal" href="_thread"><code>_thread</code> — Low-level threading API</a></li> </ul>  <div class="_attribution">
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