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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"

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<title>17.8. _thread — Low-level threading API — Python 3.7.0 說明文件</title>

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<span id="thread-low-level-threading-api"></span><h1>17.8. <a class="reference internal" href="#module-_thread" title="_thread: Low-level threading API."><code class="xref py py-mod docutils literal notranslate"><span class="pre">_thread</span></code></a> — Low-level threading API<a class="headerlink" href="#module-_thread" title="本標題的永久連結">¶</a></h1>

<p>This module provides low-level primitives for working with multiple threads

(also called <em class="dfn">light-weight processes</em> or <em class="dfn">tasks</em>) — multiple threads of

control sharing their global data space. For synchronization, simple locks

(also called <em class="dfn">mutexes</em> or <em class="dfn">binary semaphores</em>) are provided.

The <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-level

threading API built on top of this module.</p>

<p><span class="versionmodified">3.7 版更變: </span>This module used to be optional, it is now always available.</p>

</div>

<p>This module defines the following constants and functions:</p>

<em class="property">exception </em><code class="descclassname">_thread.</code><code class="descname">error</code><a class="headerlink" href="#_thread.error" title="本定義的永久連結">¶</a></dt>

<dd><p>Raised on thread-specific errors.</p>

<p><span class="versionmodified">3.3 版更變: </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>

</div>

</dd></dl>

<code class="descclassname">_thread.</code><code class="descname">LockType</code><a class="headerlink" href="#_thread.LockType" title="本定義的永久連結">¶</a></dt>

<dd><p>This is the type of lock objects.</p>

</dd></dl>

<code class="descclassname">_thread.</code><code class="descname">start_new_thread</code><span class="sig-paren">(</span><em>function</em>, <em>args</em><span class="optional">[</span>, <em>kwargs</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#_thread.start_new_thread" title="本定義的永久連結">¶</a></dt>

<dd><p>Start a new thread and return its identifier. The thread executes the function

<em>function</em> with the argument list <em>args</em> (which must be a tuple). The optional

<em>kwargs</em> argument specifies a dictionary of keyword arguments. When the function

returns, the thread silently exits. When the function terminates with an

unhandled exception, a stack trace is printed and then the thread exits (but

other threads continue to run).</p>

</dd></dl>

<code class="descclassname">_thread.</code><code class="descname">interrupt_main</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#_thread.interrupt_main" title="本定義的永久連結">¶</a></dt>

<dd><p>Raise a <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> exception in the main thread. A subthread can

use this function to interrupt the main thread.</p>

</dd></dl>

<code class="descclassname">_thread.</code><code class="descname">exit</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#_thread.exit" title="本定義的永久連結">¶</a></dt>

<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 the

thread to exit silently.</p>

</dd></dl>

<code class="descclassname">_thread.</code><code class="descname">allocate_lock</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#_thread.allocate_lock" title="本定義的永久連結">¶</a></dt>

<dd><p>Return a new lock object. Methods of locks are described below. The lock is

initially unlocked.</p>

</dd></dl>

<code class="descclassname">_thread.</code><code class="descname">get_ident</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#_thread.get_ident" title="本定義的永久連結">¶</a></dt>

<dd><p>Return the 『thread identifier』 of the current thread. This is a nonzero

integer. Its value has no direct meaning; it is intended as a magic cookie to

be used e.g. to index a dictionary of thread-specific data. Thread identifiers

may be recycled when a thread exits and another thread is created.</p>

</dd></dl>

<code class="descclassname">_thread.</code><code class="descname">stack_size</code><span class="sig-paren">(</span><span class="optional">[</span><em>size</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#_thread.stack_size" title="本定義的永久連結">¶</a></dt>

<dd><p>Return the thread stack size used when creating new threads. The optional

<em>size</em> argument specifies the stack size to be used for subsequently created

threads, and must be 0 (use platform or configured default) or a positive

integer value of at least 32,768 (32 KiB). If <em>size</em> is not specified,

0 is used. If changing the thread stack size is

unsupported, 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 is

invalid, 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 KiB

is currently the minimum supported stack size value to guarantee sufficient

stack space for the interpreter itself. Note that some platforms may have

particular restrictions on values for the stack size, such as requiring a

minimum stack size > 32 KiB or requiring allocation in multiples of the system

memory page size - platform documentation should be referred to for more

information (4 KiB pages are common; using multiples of 4096 for the stack size is

the suggested approach in the absence of more specific information).

Availability: Windows, systems with POSIX threads.</p>

</dd></dl>

<code class="descclassname">_thread.</code><code class="descname">TIMEOUT_MAX</code><a class="headerlink" href="#_thread.TIMEOUT_MAX" title="本定義的永久連結">¶</a></dt>

<dd><p>The maximum value allowed for the <em>timeout</em> parameter of

<code class="xref py py-meth docutils literal notranslate"><span class="pre">Lock.acquire()</span></code>. Specifying a timeout greater than 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>

</div>

</dd></dl>

<p>Lock objects have the following methods:</p>

<code class="descclassname">lock.</code><code class="descname">acquire</code><span class="sig-paren">(</span><em>waitflag=1</em>, <em>timeout=-1</em><span class="sig-paren">)</span><a class="headerlink" href="#_thread.lock.acquire" title="本定義的永久連結">¶</a></dt>

<dd><p>Without any optional argument, this method acquires the lock unconditionally, if

necessary waiting until it is released by another thread (only one thread at a

time can acquire a lock — that’s their reason for existence).</p>

<p>If the integer <em>waitflag</em> argument is present, the action depends on its

value: if it is zero, the lock is only acquired if it can be acquired

immediately without waiting, while if it is nonzero, the lock is acquired

unconditionally as above.</p>

<p>If the floating-point <em>timeout</em> argument is present and positive, it

specifies the maximum wait time in seconds before returning. A negative

<em>timeout</em> argument specifies an unbounded wait. You cannot specify

a <em>timeout</em> if <em>waitflag</em> is zero.</p>

<p>The return value is <code class="docutils literal notranslate"><span class="pre">True</span></code> if the lock is acquired successfully,

<code class="docutils literal notranslate"><span class="pre">False</span></code> if not.</p>

<p><span class="versionmodified">3.2 版更變: </span>The <em>timeout</em> parameter is new.</p>

</div>

<p><span class="versionmodified">3.2 版更變: </span>Lock acquires can now be interrupted by signals on POSIX.</p>

</div>

</dd></dl>

<code class="descclassname">lock.</code><code class="descname">release</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#_thread.lock.release" title="本定義的永久連結">¶</a></dt>

<dd><p>Releases the lock. The lock must have been acquired earlier, but not

necessarily by the same thread.</p>

</dd></dl>

<code class="descclassname">lock.</code><code class="descname">locked</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#_thread.lock.locked" title="本定義的永久連結">¶</a></dt>

<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,

<code class="docutils literal notranslate"><span class="pre">False</span></code> if not.</p>

</dd></dl>

<p>In addition to these methods, lock objects can also be used 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, e.g.:</p>

<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">_thread</span>

<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>

<span class="nb">print</span><span class="p">(</span><span class="s2">"a_lock is locked while this executes"</span><span class="p">)</span>

</pre></div>

</div>

<p><strong>Caveats:</strong></p>

<li>Threads interact strangely with interrupts: 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>

exception will be received by an arbitrary thread. (When the <a class="reference internal" href="signal.html#module-signal" title="signal: Set handlers for asynchronous events."><code class="xref py py-mod docutils literal notranslate"><span class="pre">signal</span></code></a>

module is available, interrupts always go to the main thread.)</li>

<li>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 is

equivalent 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>.</li>

<li>It is not possible to interrupt the <code class="xref py py-meth docutils literal notranslate"><span class="pre">acquire()</span></code> method on a lock — 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> exception will happen after the lock has been acquired.</li>

<li>When the main thread exits, it is system defined whether the other threads

survive. On most systems, they are killed without executing

<a class="reference internal" href="../reference/compound_stmts.html#try"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">try</span></code></a> … <a class="reference internal" href="../reference/compound_stmts.html#finally"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">finally</span></code></a> clauses or executing object

destructors.</li>

<li>When the main thread exits, it does not do any of its usual cleanup (except

that <a class="reference internal" href="../reference/compound_stmts.html#try"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">try</span></code></a> … <a class="reference internal" href="../reference/compound_stmts.html#finally"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">finally</span></code></a> clauses are honored), and the

standard I/O files are not flushed.</li>

</ul>

</div>

<p class="topless"><a href="queue.html"

title="上一章">17.7. <code class="docutils literal notranslate"><span class="pre">queue</span></code> — A synchronized queue class</a></p>

<p class="topless"><a href="_dummy_thread.html"

title="下一章">17.9. <code class="docutils literal notranslate"><span class="pre">_dummy_thread</span></code> — Drop-in replacement for the <code class="docutils literal notranslate"><span class="pre">_thread</span></code> module</a></p>

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