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<section id="thread-local-storage-support">
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<span id="thread-local-storage"></span><h1>Thread-local storage support<a class="headerlink" href="#thread-local-storage-support" title="Link to this heading">¶</a></h1>
|
||
<p>The Python interpreter provides low-level support for thread-local storage
|
||
(TLS) which wraps the underlying native TLS implementation to support the
|
||
Python-level thread-local storage API (<a class="reference internal" href="../library/threading.html#threading.local" title="threading.local"><code class="xref py py-class docutils literal notranslate"><span class="pre">threading.local</span></code></a>). The
|
||
CPython C level APIs are similar to those offered by pthreads and Windows:
|
||
use a thread key and functions to associate a <span class="c-expr sig sig-inline c"><span class="kt">void</span><span class="p">*</span></span> value per
|
||
thread.</p>
|
||
<p>A <a class="reference internal" href="../glossary.html#term-thread-state"><span class="xref std std-term">thread state</span></a> does <em>not</em> need to be <a class="reference internal" href="../glossary.html#term-attached-thread-state"><span class="xref std std-term">attached</span></a>
|
||
when calling these functions; they supply their own locking.</p>
|
||
<p>Note that <code class="file docutils literal notranslate"><span class="pre">Python.h</span></code> does not include the declaration of the TLS APIs,
|
||
you need to include <code class="file docutils literal notranslate"><span class="pre">pythread.h</span></code> to use thread-local storage.</p>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">Note</p>
|
||
<p>None of these API functions handle memory management on behalf of the
|
||
<span class="c-expr sig sig-inline c"><span class="kt">void</span><span class="p">*</span></span> values. You need to allocate and deallocate them yourself.
|
||
If the <span class="c-expr sig sig-inline c"><span class="kt">void</span><span class="p">*</span></span> values happen to be <span class="c-expr sig sig-inline c"><a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n">PyObject</span></a><span class="p">*</span></span>, these
|
||
functions don’t do refcount operations on them either.</p>
|
||
</div>
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<section id="thread-specific-storage-api">
|
||
<span id="id1"></span><h2>Thread-specific storage API<a class="headerlink" href="#thread-specific-storage-api" title="Link to this heading">¶</a></h2>
|
||
<p>The thread-specific storage (TSS) API was introduced to supersede the use of the existing TLS API within the
|
||
CPython interpreter. This API uses a new type <a class="reference internal" href="#c.Py_tss_t" title="Py_tss_t"><code class="xref c c-type docutils literal notranslate"><span class="pre">Py_tss_t</span></code></a> instead of
|
||
<span class="c-expr sig sig-inline c"><span class="kt">int</span></span> to represent thread keys.</p>
|
||
<div class="versionadded">
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||
<p><span class="versionmodified added">Added in version 3.7.</span></p>
|
||
</div>
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||
<div class="admonition seealso">
|
||
<p class="admonition-title">See also</p>
|
||
<p>“A New C-API for Thread-Local Storage in CPython” (<span class="target" id="index-0"></span><a class="pep reference external" href="https://peps.python.org/pep-0539/"><strong>PEP 539</strong></a>)</p>
|
||
</div>
|
||
<dl class="c type">
|
||
<dt class="sig sig-object c" id="c.Py_tss_t">
|
||
<span class="k"><span class="pre">type</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">Py_tss_t</span></span></span><a class="headerlink" href="#c.Py_tss_t" title="Link to this definition">¶</a><br /></dt>
|
||
<dd><p>This data structure represents the state of a thread key, the definition of
|
||
which may depend on the underlying TLS implementation, and it has an
|
||
internal field representing the key’s initialization state. There are no
|
||
public members in this structure.</p>
|
||
<p>When <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Py_LIMITED_API</span></a> is not defined, static allocation of
|
||
this type by <a class="reference internal" href="#c.Py_tss_NEEDS_INIT" title="Py_tss_NEEDS_INIT"><code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_tss_NEEDS_INIT</span></code></a> is allowed.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="c macro">
|
||
<dt class="sig sig-object c" id="c.Py_tss_NEEDS_INIT">
|
||
<span class="sig-name descname"><span class="n"><span class="pre">Py_tss_NEEDS_INIT</span></span></span><a class="headerlink" href="#c.Py_tss_NEEDS_INIT" title="Link to this definition">¶</a><br /></dt>
|
||
<dd><p>This macro expands to the initializer for <a class="reference internal" href="#c.Py_tss_t" title="Py_tss_t"><code class="xref c c-type docutils literal notranslate"><span class="pre">Py_tss_t</span></code></a> variables.
|
||
Note that this macro won’t be defined with <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Py_LIMITED_API</span></a>.</p>
|
||
</dd></dl>
|
||
|
||
</section>
|
||
<section id="dynamic-allocation">
|
||
<h2>Dynamic allocation<a class="headerlink" href="#dynamic-allocation" title="Link to this heading">¶</a></h2>
|
||
<p>Dynamic allocation of the <a class="reference internal" href="#c.Py_tss_t" title="Py_tss_t"><code class="xref c c-type docutils literal notranslate"><span class="pre">Py_tss_t</span></code></a>, required in extension modules
|
||
built with <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Py_LIMITED_API</span></a>, where static allocation of this type
|
||
is not possible due to its implementation being opaque at build time.</p>
|
||
<dl class="c function">
|
||
<dt class="sig sig-object c" id="c.PyThread_tss_alloc">
|
||
<a class="reference internal" href="#c.Py_tss_t" title="Py_tss_t"><span class="n"><span class="pre">Py_tss_t</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyThread_tss_alloc</span></span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyThread_tss_alloc" title="Link to this definition">¶</a><br /></dt>
|
||
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a> since version 3.7.</em><p>Return a value which is the same state as a value initialized with
|
||
<a class="reference internal" href="#c.Py_tss_NEEDS_INIT" title="Py_tss_NEEDS_INIT"><code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_tss_NEEDS_INIT</span></code></a>, or <code class="docutils literal notranslate"><span class="pre">NULL</span></code> in the case of dynamic allocation
|
||
failure.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="c function">
|
||
<dt class="sig sig-object c" id="c.PyThread_tss_free">
|
||
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyThread_tss_free</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="#c.Py_tss_t" title="Py_tss_t"><span class="n"><span class="pre">Py_tss_t</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">key</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyThread_tss_free" title="Link to this definition">¶</a><br /></dt>
|
||
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a> since version 3.7.</em><p>Free the given <em>key</em> allocated by <a class="reference internal" href="#c.PyThread_tss_alloc" title="PyThread_tss_alloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyThread_tss_alloc()</span></code></a>, after
|
||
first calling <a class="reference internal" href="#c.PyThread_tss_delete" title="PyThread_tss_delete"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyThread_tss_delete()</span></code></a> to ensure any associated
|
||
thread locals have been unassigned. This is a no-op if the <em>key</em>
|
||
argument is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">Note</p>
|
||
<p>A freed key becomes a dangling pointer. You should reset the key to
|
||
<code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
</section>
|
||
<section id="methods">
|
||
<h2>Methods<a class="headerlink" href="#methods" title="Link to this heading">¶</a></h2>
|
||
<p>The parameter <em>key</em> of these functions must not be <code class="docutils literal notranslate"><span class="pre">NULL</span></code>. Moreover, the
|
||
behaviors of <a class="reference internal" href="#c.PyThread_tss_set" title="PyThread_tss_set"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyThread_tss_set()</span></code></a> and <a class="reference internal" href="#c.PyThread_tss_get" title="PyThread_tss_get"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyThread_tss_get()</span></code></a> are
|
||
undefined if the given <a class="reference internal" href="#c.Py_tss_t" title="Py_tss_t"><code class="xref c c-type docutils literal notranslate"><span class="pre">Py_tss_t</span></code></a> has not been initialized by
|
||
<a class="reference internal" href="#c.PyThread_tss_create" title="PyThread_tss_create"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyThread_tss_create()</span></code></a>.</p>
|
||
<dl class="c function">
|
||
<dt class="sig sig-object c" id="c.PyThread_tss_is_created">
|
||
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyThread_tss_is_created</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="#c.Py_tss_t" title="Py_tss_t"><span class="n"><span class="pre">Py_tss_t</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">key</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyThread_tss_is_created" title="Link to this definition">¶</a><br /></dt>
|
||
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a> since version 3.7.</em><p>Return a non-zero value if the given <a class="reference internal" href="#c.Py_tss_t" title="Py_tss_t"><code class="xref c c-type docutils literal notranslate"><span class="pre">Py_tss_t</span></code></a> has been initialized
|
||
by <a class="reference internal" href="#c.PyThread_tss_create" title="PyThread_tss_create"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyThread_tss_create()</span></code></a>.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="c function">
|
||
<dt class="sig sig-object c" id="c.PyThread_tss_create">
|
||
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyThread_tss_create</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="#c.Py_tss_t" title="Py_tss_t"><span class="n"><span class="pre">Py_tss_t</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">key</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyThread_tss_create" title="Link to this definition">¶</a><br /></dt>
|
||
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a> since version 3.7.</em><p>Return a zero value on successful initialization of a TSS key. The behavior
|
||
is undefined if the value pointed to by the <em>key</em> argument is not
|
||
initialized by <a class="reference internal" href="#c.Py_tss_NEEDS_INIT" title="Py_tss_NEEDS_INIT"><code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_tss_NEEDS_INIT</span></code></a>. This function can be called
|
||
repeatedly on the same key – calling it on an already initialized key is a
|
||
no-op and immediately returns success.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="c function">
|
||
<dt class="sig sig-object c" id="c.PyThread_tss_delete">
|
||
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyThread_tss_delete</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="#c.Py_tss_t" title="Py_tss_t"><span class="n"><span class="pre">Py_tss_t</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">key</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyThread_tss_delete" title="Link to this definition">¶</a><br /></dt>
|
||
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a> since version 3.7.</em><p>Destroy a TSS key to forget the values associated with the key across all
|
||
threads, and change the key’s initialization state to uninitialized. A
|
||
destroyed key is able to be initialized again by
|
||
<a class="reference internal" href="#c.PyThread_tss_create" title="PyThread_tss_create"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyThread_tss_create()</span></code></a>. This function can be called repeatedly on
|
||
the same key – calling it on an already destroyed key is a no-op.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="c function">
|
||
<dt class="sig sig-object c" id="c.PyThread_tss_set">
|
||
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyThread_tss_set</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="#c.Py_tss_t" title="Py_tss_t"><span class="n"><span class="pre">Py_tss_t</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">key</span></span>, <span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">value</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyThread_tss_set" title="Link to this definition">¶</a><br /></dt>
|
||
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a> since version 3.7.</em><p>Return a zero value to indicate successfully associating a <span class="c-expr sig sig-inline c"><span class="kt">void</span><span class="p">*</span></span>
|
||
value with a TSS key in the current thread. Each thread has a distinct
|
||
mapping of the key to a <span class="c-expr sig sig-inline c"><span class="kt">void</span><span class="p">*</span></span> value.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="c function">
|
||
<dt class="sig sig-object c" id="c.PyThread_tss_get">
|
||
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyThread_tss_get</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="#c.Py_tss_t" title="Py_tss_t"><span class="n"><span class="pre">Py_tss_t</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">key</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyThread_tss_get" title="Link to this definition">¶</a><br /></dt>
|
||
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a> since version 3.7.</em><p>Return the <span class="c-expr sig sig-inline c"><span class="kt">void</span><span class="p">*</span></span> value associated with a TSS key in the current
|
||
thread. This returns <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if no value is associated with the key in the
|
||
current thread.</p>
|
||
</dd></dl>
|
||
|
||
</section>
|
||
<section id="legacy-apis">
|
||
<span id="thread-local-storage-api"></span><h2>Legacy APIs<a class="headerlink" href="#legacy-apis" title="Link to this heading">¶</a></h2>
|
||
<div class="deprecated">
|
||
<p><span class="versionmodified deprecated">Deprecated since version 3.7: </span>This API is superseded by the
|
||
<a class="reference internal" href="#thread-specific-storage-api"><span class="std std-ref">thread-specific storage (TSS) API</span></a>.</p>
|
||
</div>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">Note</p>
|
||
<p>This version of the API does not support platforms where the native TLS key
|
||
is defined in a way that cannot be safely cast to <code class="docutils literal notranslate"><span class="pre">int</span></code>. On such platforms,
|
||
<a class="reference internal" href="#c.PyThread_create_key" title="PyThread_create_key"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyThread_create_key()</span></code></a> will return immediately with a failure status,
|
||
and the other TLS functions will all be no-ops on such platforms.</p>
|
||
</div>
|
||
<p>Due to the compatibility problem noted above, this version of the API should not
|
||
be used in new code.</p>
|
||
<dl class="c function">
|
||
<dt class="sig sig-object c" id="c.PyThread_create_key">
|
||
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyThread_create_key</span></span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyThread_create_key" title="Link to this definition">¶</a><br /></dt>
|
||
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em></dd></dl>
|
||
|
||
<dl class="c function">
|
||
<dt class="sig sig-object c" id="c.PyThread_delete_key">
|
||
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyThread_delete_key</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">key</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyThread_delete_key" title="Link to this definition">¶</a><br /></dt>
|
||
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em></dd></dl>
|
||
|
||
<dl class="c function">
|
||
<dt class="sig sig-object c" id="c.PyThread_set_key_value">
|
||
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyThread_set_key_value</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">key</span></span>, <span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">value</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyThread_set_key_value" title="Link to this definition">¶</a><br /></dt>
|
||
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em></dd></dl>
|
||
|
||
<dl class="c function">
|
||
<dt class="sig sig-object c" id="c.PyThread_get_key_value">
|
||
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyThread_get_key_value</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">key</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyThread_get_key_value" title="Link to this definition">¶</a><br /></dt>
|
||
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em></dd></dl>
|
||
|
||
<dl class="c function">
|
||
<dt class="sig sig-object c" id="c.PyThread_delete_key_value">
|
||
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyThread_delete_key_value</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">key</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyThread_delete_key_value" title="Link to this definition">¶</a><br /></dt>
|
||
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em></dd></dl>
|
||
|
||
<dl class="c function">
|
||
<dt class="sig sig-object c" id="c.PyThread_ReInitTLS">
|
||
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyThread_ReInitTLS</span></span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyThread_ReInitTLS" title="Link to this definition">¶</a><br /></dt>
|
||
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em></dd></dl>
|
||
|
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|
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|
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<li><a class="reference internal" href="#">Thread-local storage support</a><ul>
|
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|
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|
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|
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|
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