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199 </ul>200 </div> 201 202 <div class="document">203 <div class="documentwrapper">204 <div class="bodywrapper">205 <div class="body" role="main">206 207 <section id="module-_thread">208<span id="thread-low-level-threading-api"></span><h1><code class="xref py py-mod docutils literal notranslate"><span class="pre">_thread</span></code> — Low-level threading API<a class="headerlink" href="#module-_thread" title="Link to this heading">¶</a></h1>209<hr class="docutils" id="index-0" />210<p>This module provides low-level primitives for working with multiple threads211(also called <em class="dfn">light-weight processes</em> or <em class="dfn">tasks</em>) — multiple threads of212control sharing their global data space. For synchronization, simple locks213(also called <em class="dfn">mutexes</em> or <em class="dfn">binary semaphores</em>) are provided.214The <a class="reference internal" href="threading.html#module-threading" title="threading: Thread-based parallelism."><code class="xref py py-mod docutils literal notranslate"><span class="pre">threading</span></code></a> module provides an easier to use and higher-level215threading API built on top of this module.</p>216<div class="versionchanged" id="index-1">217<p><span class="versionmodified changed">Changed in version 3.7: </span>This module used to be optional, it is now always available.</p>218</div>219<p>This module defines the following constants and functions:</p>220<dl class="py exception">221<dt class="sig sig-object py" id="thread.error">222<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">_thread.</span></span><span class="sig-name descname"><span class="pre">error</span></span><a class="headerlink" href="#thread.error" title="Link to this definition">¶</a></dt>223<dd><p>Raised on thread-specific errors.</p>224<div class="versionchanged">225<p><span class="versionmodified changed">Changed in version 3.3: </span>This is now a synonym of the built-in <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>226</div>227</dd></dl>228 229<dl class="py data">230<dt class="sig sig-object py" id="thread.LockType">231<span class="sig-prename descclassname"><span class="pre">_thread.</span></span><span class="sig-name descname"><span class="pre">LockType</span></span><a class="headerlink" href="#thread.LockType" title="Link to this definition">¶</a></dt>232<dd><p>This is the type of lock objects.</p>233</dd></dl>234 235<dl class="py function">236<dt class="sig sig-object py" id="thread.start_new_thread">237<span class="sig-prename descclassname"><span class="pre">_thread.</span></span><span class="sig-name descname"><span class="pre">start_new_thread</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">function</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">args</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">kwargs</span></span></em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#thread.start_new_thread" title="Link to this definition">¶</a></dt>238<dd><p>Start a new thread and return its identifier. The thread executes the239function <em>function</em> with the argument list <em>args</em> (which must be a tuple).240The optional <em>kwargs</em> argument specifies a dictionary of keyword arguments.</p>241<p>When the function returns, the thread silently exits.</p>242<p>When the function terminates with an unhandled exception,243<a class="reference internal" href="sys.html#sys.unraisablehook" title="sys.unraisablehook"><code class="xref py py-func docutils literal notranslate"><span class="pre">sys.unraisablehook()</span></code></a> is called to handle the exception. The <em>object</em>244attribute of the hook argument is <em>function</em>. By default, a stack trace is245printed and then the thread exits (but other threads continue to run).</p>246<p>When the function raises a <a class="reference internal" href="exceptions.html#SystemExit" title="SystemExit"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SystemExit</span></code></a> exception, it is silently247ignored.</p>248<p class="audit-hook">Raises an <a class="reference internal" href="sys.html#auditing"><span class="std std-ref">auditing event</span></a> <code class="docutils literal notranslate"><span class="pre">_thread.start_new_thread</span></code> with arguments <code class="docutils literal notranslate"><span class="pre">function</span></code>, <code class="docutils literal notranslate"><span class="pre">args</span></code>, <code class="docutils literal notranslate"><span class="pre">kwargs</span></code>.</p>249<div class="versionchanged">250<p><span class="versionmodified changed">Changed in version 3.8: </span><a class="reference internal" href="sys.html#sys.unraisablehook" title="sys.unraisablehook"><code class="xref py py-func docutils literal notranslate"><span class="pre">sys.unraisablehook()</span></code></a> is now used to handle unhandled exceptions.</p>251</div>252</dd></dl>253 254<dl class="py function">255<dt class="sig sig-object py" id="thread.interrupt_main">256<span class="sig-prename descclassname"><span class="pre">_thread.</span></span><span class="sig-name descname"><span class="pre">interrupt_main</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">signum</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">signal.SIGINT</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><span class="sig-paren">)</span><a class="headerlink" href="#thread.interrupt_main" title="Link to this definition">¶</a></dt>257<dd><p>Simulate the effect of a signal arriving in the main thread.258A thread can use this function to interrupt the main thread, though259there is no guarantee that the interruption will happen immediately.</p>260<p>If given, <em>signum</em> is the number of the signal to simulate.261If <em>signum</em> is not given, <a class="reference internal" href="signal.html#signal.SIGINT" title="signal.SIGINT"><code class="xref py py-const docutils literal notranslate"><span class="pre">signal.SIGINT</span></code></a> is simulated.</p>262<p>If the given signal isn’t handled by Python (it was set to263<a class="reference internal" href="signal.html#signal.SIG_DFL" title="signal.SIG_DFL"><code class="xref py py-const docutils literal notranslate"><span class="pre">signal.SIG_DFL</span></code></a> or <a class="reference internal" href="signal.html#signal.SIG_IGN" title="signal.SIG_IGN"><code class="xref py py-const docutils literal notranslate"><span class="pre">signal.SIG_IGN</span></code></a>), this function does264nothing.</p>265<div class="versionchanged">266<p><span class="versionmodified changed">Changed in version 3.10: </span>The <em>signum</em> argument is added to customize the signal number.</p>267</div>268<div class="admonition note">269<p class="admonition-title">Note</p>270<p>This does not emit the corresponding signal but schedules a call to271the associated handler (if it exists).272If you want to truly emit the signal, use <a class="reference internal" href="signal.html#signal.raise_signal" title="signal.raise_signal"><code class="xref py py-func docutils literal notranslate"><span class="pre">signal.raise_signal()</span></code></a>.</p>273</div>274</dd></dl>275 276<dl class="py function">277<dt class="sig sig-object py" id="thread.exit">278<span class="sig-prename descclassname"><span class="pre">_thread.</span></span><span class="sig-name descname"><span class="pre">exit</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#thread.exit" title="Link to this definition">¶</a></dt>279<dd><p>Raise the <a class="reference internal" href="exceptions.html#SystemExit" title="SystemExit"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SystemExit</span></code></a> exception. When not caught, this will cause the280thread to exit silently.</p>281</dd></dl>282 283<dl class="py function">284<dt class="sig sig-object py" id="thread.allocate_lock">285<span class="sig-prename descclassname"><span class="pre">_thread.</span></span><span class="sig-name descname"><span class="pre">allocate_lock</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#thread.allocate_lock" title="Link to this definition">¶</a></dt>286<dd><p>Return a new lock object. Methods of locks are described below. The lock is287initially unlocked.</p>288</dd></dl>289 290<dl class="py function">291<dt class="sig sig-object py" id="thread.get_ident">292<span class="sig-prename descclassname"><span class="pre">_thread.</span></span><span class="sig-name descname"><span class="pre">get_ident</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#thread.get_ident" title="Link to this definition">¶</a></dt>293<dd><p>Return the ‘thread identifier’ of the current thread. This is a nonzero294integer. Its value has no direct meaning; it is intended as a magic cookie to295be used e.g. to index a dictionary of thread-specific data. Thread identifiers296may be recycled when a thread exits and another thread is created.</p>297</dd></dl>298 299<dl class="py function">300<dt class="sig sig-object py" id="thread.get_native_id">301<span class="sig-prename descclassname"><span class="pre">_thread.</span></span><span class="sig-name descname"><span class="pre">get_native_id</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#thread.get_native_id" title="Link to this definition">¶</a></dt>302<dd><p>Return the native integral Thread ID of the current thread assigned by the kernel.303This is a non-negative integer.304Its value may be used to uniquely identify this particular thread system-wide305(until the thread terminates, after which the value may be recycled by the OS).</p>306<div class="availability docutils container">307<p><a class="reference internal" href="intro.html#availability"><span class="std std-ref">Availability</span></a>: Windows, FreeBSD, Linux, macOS, OpenBSD, NetBSD, AIX, DragonFlyBSD, GNU/kFreeBSD, Solaris.</p>308</div>309<div class="versionadded">310<p><span class="versionmodified added">Added in version 3.8.</span></p>311</div>312<div class="versionchanged">313<p><span class="versionmodified changed">Changed in version 3.13: </span>Added support for GNU/kFreeBSD.</p>314</div>315<div class="versionchanged">316<p><span class="versionmodified changed">Changed in version 3.15: </span>Added support for Solaris.</p>317</div>318</dd></dl>319 320<dl class="py function">321<dt class="sig sig-object py" id="thread.stack_size">322<span class="sig-prename descclassname"><span class="pre">_thread.</span></span><span class="sig-name descname"><span class="pre">stack_size</span></span><span class="sig-paren">(</span><span class="optional">[</span><em class="sig-param"><span class="n"><span class="pre">size</span></span></em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#thread.stack_size" title="Link to this definition">¶</a></dt>323<dd><p>Return the thread stack size used when creating new threads. The optional324<em>size</em> argument specifies the stack size to be used for subsequently created325threads, and must be 0 (use platform or configured default) or a positive326integer value of at least 32,768 (32 KiB). If <em>size</em> is not specified,3270 is used. If changing the thread stack size is328unsupported, a <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> is raised. If the specified stack size is329invalid, 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> is raised and the stack size is unmodified. 32 KiB330is currently the minimum supported stack size value to guarantee sufficient331stack space for the interpreter itself. Note that some platforms may have332particular restrictions on values for the stack size, such as requiring a333minimum stack size > 32 KiB or requiring allocation in multiples of the system334memory page size - platform documentation should be referred to for more335information (4 KiB pages are common; using multiples of 4096 for the stack size is336the suggested approach in the absence of more specific information).</p>337<div class="availability docutils container">338<p><a class="reference internal" href="intro.html#availability"><span class="std std-ref">Availability</span></a>: Windows, pthreads.</p>339<p>Unix platforms with POSIX threads support.</p>340</div>341</dd></dl>342 343<dl class="py data">344<dt class="sig sig-object py" id="thread.TIMEOUT_MAX">345<span class="sig-prename descclassname"><span class="pre">_thread.</span></span><span class="sig-name descname"><span class="pre">TIMEOUT_MAX</span></span><a class="headerlink" href="#thread.TIMEOUT_MAX" title="Link to this definition">¶</a></dt>346<dd><p>The maximum value allowed for the <em>timeout</em> parameter of347<a class="reference internal" href="threading.html#threading.Lock.acquire" title="threading.Lock.acquire"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Lock.acquire</span></code></a>. Specifying a timeout greater348than this value will raise an <a class="reference internal" href="exceptions.html#OverflowError" title="OverflowError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OverflowError</span></code></a>.</p>349<div class="versionadded">350<p><span class="versionmodified added">Added in version 3.2.</span></p>351</div>352</dd></dl>353 354<p>Lock objects have the following methods:</p>355<dl class="py method">356<dt class="sig sig-object py" id="thread.lock.acquire">357<span class="sig-prename descclassname"><span class="pre">lock.</span></span><span class="sig-name descname"><span class="pre">acquire</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">blocking</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="n"><span class="pre">timeout</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">-1</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#thread.lock.acquire" title="Link to this definition">¶</a></dt>358<dd><p>Without any optional argument, this method acquires the lock unconditionally, if359necessary waiting until it is released by another thread (only one thread at a360time can acquire a lock — that’s their reason for existence).</p>361<p>If the <em>blocking</em> argument is present, the action depends on its362value: if it is false, the lock is only acquired if it can be acquired363immediately without waiting, while if it is true, the lock is acquired364unconditionally as above.</p>365<p>If the floating-point <em>timeout</em> argument is present and positive, it366specifies the maximum wait time in seconds before returning. A negative367<em>timeout</em> argument specifies an unbounded wait. You cannot specify368a <em>timeout</em> if <em>blocking</em> is false.</p>369<p>The return value is <code class="docutils literal notranslate"><span class="pre">True</span></code> if the lock is acquired successfully,370<code class="docutils literal notranslate"><span class="pre">False</span></code> if not.</p>371<div class="versionchanged">372<p><span class="versionmodified changed">Changed in version 3.2: </span>The <em>timeout</em> parameter is new.</p>373</div>374<div class="versionchanged">375<p><span class="versionmodified changed">Changed in version 3.2: </span>Lock acquires can now be interrupted by signals on POSIX.</p>376</div>377<div class="versionchanged">378<p><span class="versionmodified changed">Changed in version 3.14: </span>Lock acquires can now be interrupted by signals on Windows.</p>379</div>380</dd></dl>381 382<dl class="py method">383<dt class="sig sig-object py" id="thread.lock.release">384<span class="sig-prename descclassname"><span class="pre">lock.</span></span><span class="sig-name descname"><span class="pre">release</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#thread.lock.release" title="Link to this definition">¶</a></dt>385<dd><p>Releases the lock. The lock must have been acquired earlier, but not386necessarily by the same thread.</p>387</dd></dl>388 389<dl class="py method">390<dt class="sig sig-object py" id="thread.lock.locked">391<span class="sig-prename descclassname"><span class="pre">lock.</span></span><span class="sig-name descname"><span class="pre">locked</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#thread.lock.locked" title="Link to this definition">¶</a></dt>392<dd><p>Return the status of the lock: <code class="docutils literal notranslate"><span class="pre">True</span></code> if it has been acquired by some thread,393<code class="docutils literal notranslate"><span class="pre">False</span></code> if not.</p>394</dd></dl>395 396<p>In addition to these methods, lock objects can also be used via the397<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, e.g.:</p>398<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">_thread</span>399 400<span class="n">a_lock</span> <span class="o">=</span> <span class="n">_thread</span><span class="o">.</span><span class="n">allocate_lock</span><span class="p">()</span>401 402<span class="k">with</span> <span class="n">a_lock</span><span class="p">:</span>403 <span class="nb">print</span><span class="p">(</span><span class="s2">"a_lock is locked while this executes"</span><span class="p">)</span>404</pre></div>405</div>406<p><strong>Caveats:</strong></p>407<ul class="simple" id="index-2">408<li><p>Interrupts always go to the main thread (the <a class="reference internal" href="exceptions.html#KeyboardInterrupt" title="KeyboardInterrupt"><code class="xref py py-exc docutils literal notranslate"><span class="pre">KeyboardInterrupt</span></code></a>409exception will be received by that thread.)</p></li>410<li><p>Calling <a class="reference internal" href="sys.html#sys.exit" title="sys.exit"><code class="xref py py-func docutils literal notranslate"><span class="pre">sys.exit()</span></code></a> or raising the <a class="reference internal" href="exceptions.html#SystemExit" title="SystemExit"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SystemExit</span></code></a> exception is411equivalent to calling <a class="reference internal" href="#thread.exit" title="_thread.exit"><code class="xref py py-func docutils literal notranslate"><span class="pre">_thread.exit()</span></code></a>.</p></li>412<li><p>When the main thread exits, it is system defined whether the other threads413survive. 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