<!DOCTYPE html> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta charset="utf-8" /> <title>Memory Management — Python 3.7.10 documentation</title> <link rel="stylesheet" href="../_static/pydoctheme.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript" id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/underscore.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <script type="text/javascript" src="../_static/language_data.js"></script> <script type="text/javascript" src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 3.7.10 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="index" title="Index" href="../genindex.html" /> <link rel="search" title="Search" href="../search.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="next" title="Object Implementation Support" href="objimpl.html" /> <link rel="prev" title="Initialization, Finalization, and Threads" href="init.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="https://docs.python.org/3/c-api/memory.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> <style> @media only screen { table.full-width-table { width: 100%; } } </style> </head><body> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="objimpl.html" title="Object Implementation Support" accesskey="N">next</a> |</li> <li class="right" > <a href="init.html" title="Initialization, Finalization, and Threads" accesskey="P">previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li> <a href="../index.html">3.7.10 Documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" accesskey="U">Python/C API Reference Manual</a> »</li> <li class="right"> <div class="inline-search" style="display: none" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" type="text" name="q" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </div> <script type="text/javascript">$('.inline-search').show(0);</script> | </li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="memory-management"> <span id="memory"></span><h1>Memory Management<a class="headerlink" href="#memory-management" title="Permalink to this headline">¶</a></h1> <div class="section" id="overview"> <span id="memoryoverview"></span><h2>Overview<a class="headerlink" href="#overview" title="Permalink to this headline">¶</a></h2> <p>Memory management in Python involves a private heap containing all Python objects and data structures. The management of this private heap is ensured internally by the <em>Python memory manager</em>. The Python memory manager has different components which deal with various dynamic storage management aspects, like sharing, segmentation, preallocation or caching.</p> <p>At the lowest level, a raw memory allocator ensures that there is enough room in the private heap for storing all Python-related data by interacting with the memory manager of the operating system. On top of the raw memory allocator, several object-specific allocators operate on the same heap and implement distinct memory management policies adapted to the peculiarities of every object type. For example, integer objects are managed differently within the heap than strings, tuples or dictionaries because integers imply different storage requirements and speed/space tradeoffs. The Python memory manager thus delegates some of the work to the object-specific allocators, but ensures that the latter operate within the bounds of the private heap.</p> <p>It is important to understand that the management of the Python heap is performed by the interpreter itself and that the user has no control over it, even if they regularly manipulate object pointers to memory blocks inside that heap. The allocation of heap space for Python objects and other internal buffers is performed on demand by the Python memory manager through the Python/C API functions listed in this document.</p> <p id="index-0">To avoid memory corruption, extension writers should never try to operate on Python objects with the functions exported by the C library: <code class="xref c c-func docutils literal notranslate"><span class="pre">malloc()</span></code>, <code class="xref c c-func docutils literal notranslate"><span class="pre">calloc()</span></code>, <code class="xref c c-func docutils literal notranslate"><span class="pre">realloc()</span></code> and <code class="xref c c-func docutils literal notranslate"><span class="pre">free()</span></code>. This will result in mixed calls between the C allocator and the Python memory manager with fatal consequences, because they implement different algorithms and operate on different heaps. However, one may safely allocate and release memory blocks with the C library allocator for individual purposes, as shown in the following example:</p> <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">PyObject</span> <span class="o">*</span><span class="n">res</span><span class="p">;</span> <span class="kt">char</span> <span class="o">*</span><span class="n">buf</span> <span class="o">=</span> <span class="p">(</span><span class="kt">char</span> <span class="o">*</span><span class="p">)</span> <span class="n">malloc</span><span class="p">(</span><span class="n">BUFSIZ</span><span class="p">);</span> <span class="cm">/* for I/O */</span> <span class="k">if</span> <span class="p">(</span><span class="n">buf</span> <span class="o">==</span> <span class="nb">NULL</span><span class="p">)</span> <span class="k">return</span> <span class="n">PyErr_NoMemory</span><span class="p">();</span> <span class="p">...</span><span class="n">Do</span> <span class="n">some</span> <span class="n">I</span><span class="o">/</span><span class="n">O</span> <span class="n">operation</span> <span class="n">involving</span> <span class="n">buf</span><span class="p">...</span> <span class="n">res</span> <span class="o">=</span> <span class="n">PyBytes_FromString</span><span class="p">(</span><span class="n">buf</span><span class="p">);</span> <span class="n">free</span><span class="p">(</span><span class="n">buf</span><span class="p">);</span> <span class="cm">/* malloc'ed */</span> <span class="k">return</span> <span class="n">res</span><span class="p">;</span> </pre></div> </div> <p>In this example, the memory request for the I/O buffer is handled by the C library allocator. The Python memory manager is involved only in the allocation of the bytes object returned as a result.</p> <p>In most situations, however, it is recommended to allocate memory from the Python heap specifically because the latter is under control of the Python memory manager. For example, this is required when the interpreter is extended with new object types written in C. Another reason for using the Python heap is the desire to <em>inform</em> the Python memory manager about the memory needs of the extension module. Even when the requested memory is used exclusively for internal, highly-specific purposes, delegating all memory requests to the Python memory manager causes the interpreter to have a more accurate image of its memory footprint as a whole. Consequently, under certain circumstances, the Python memory manager may or may not trigger appropriate actions, like garbage collection, memory compaction or other preventive procedures. Note that by using the C library allocator as shown in the previous example, the allocated memory for the I/O buffer escapes completely the Python memory manager.</p> <div class="admonition seealso"> <p class="admonition-title">See also</p> <p>The <span class="target" id="index-1"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONMALLOC"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONMALLOC</span></code></a> environment variable can be used to configure the memory allocators used by Python.</p> <p>The <span class="target" id="index-2"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONMALLOCSTATS"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONMALLOCSTATS</span></code></a> environment variable can be used to print statistics of the <a class="reference internal" href="#pymalloc"><span class="std std-ref">pymalloc memory allocator</span></a> every time a new pymalloc object arena is created, and on shutdown.</p> </div> </div> <div class="section" id="raw-memory-interface"> <h2>Raw Memory Interface<a class="headerlink" href="#raw-memory-interface" title="Permalink to this headline">¶</a></h2> <p>The following function sets are wrappers to the system allocator. These functions are thread-safe, the <a class="reference internal" href="../glossary.html#term-global-interpreter-lock"><span class="xref std std-term">GIL</span></a> does not need to be held.</p> <p>The <a class="reference internal" href="#default-memory-allocators"><span class="std std-ref">default raw memory allocator</span></a> uses the following functions: <code class="xref c c-func docutils literal notranslate"><span class="pre">malloc()</span></code>, <code class="xref c c-func docutils literal notranslate"><span class="pre">calloc()</span></code>, <code class="xref c c-func docutils literal notranslate"><span class="pre">realloc()</span></code> and <code class="xref c c-func docutils literal notranslate"><span class="pre">free()</span></code>; call <code class="docutils literal notranslate"><span class="pre">malloc(1)</span></code> (or <code class="docutils literal notranslate"><span class="pre">calloc(1,</span> <span class="pre">1)</span></code>) when requesting zero bytes.</p> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.4.</span></p> </div> <dl class="function"> <dt id="c.PyMem_RawMalloc"> void* <code class="sig-name descname">PyMem_RawMalloc</code><span class="sig-paren">(</span>size_t<em> n</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_RawMalloc" title="Permalink to this definition">¶</a></dt> <dd><p>Allocates <em>n</em> bytes and returns a pointer of type <code class="xref c c-type docutils literal notranslate"><span class="pre">void*</span></code> to the allocated memory, or <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if the request fails.</p> <p>Requesting zero bytes returns a distinct non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code> pointer if possible, as if <code class="docutils literal notranslate"><span class="pre">PyMem_RawMalloc(1)</span></code> had been called instead. The memory will not have been initialized in any way.</p> </dd></dl> <dl class="function"> <dt id="c.PyMem_RawCalloc"> void* <code class="sig-name descname">PyMem_RawCalloc</code><span class="sig-paren">(</span>size_t<em> nelem</em>, size_t<em> elsize</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_RawCalloc" title="Permalink to this definition">¶</a></dt> <dd><p>Allocates <em>nelem</em> elements each whose size in bytes is <em>elsize</em> and returns a pointer of type <code class="xref c c-type docutils literal notranslate"><span class="pre">void*</span></code> to the allocated memory, or <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if the request fails. The memory is initialized to zeros.</p> <p>Requesting zero elements or elements of size zero bytes returns a distinct non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code> pointer if possible, as if <code class="docutils literal notranslate"><span class="pre">PyMem_RawCalloc(1,</span> <span class="pre">1)</span></code> had been called instead.</p> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.5.</span></p> </div> </dd></dl> <dl class="function"> <dt id="c.PyMem_RawRealloc"> void* <code class="sig-name descname">PyMem_RawRealloc</code><span class="sig-paren">(</span>void<em> *p</em>, size_t<em> n</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_RawRealloc" title="Permalink to this definition">¶</a></dt> <dd><p>Resizes the memory block pointed to by <em>p</em> to <em>n</em> bytes. The contents will be unchanged to the minimum of the old and the new sizes.</p> <p>If <em>p</em> is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, the call is equivalent to <code class="docutils literal notranslate"><span class="pre">PyMem_RawMalloc(n)</span></code>; else if <em>n</em> is equal to zero, the memory block is resized but is not freed, and the returned pointer is non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p> <p>Unless <em>p</em> is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, it must have been returned by a previous call to <a class="reference internal" href="#c.PyMem_RawMalloc" title="PyMem_RawMalloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawMalloc()</span></code></a>, <a class="reference internal" href="#c.PyMem_RawRealloc" title="PyMem_RawRealloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawRealloc()</span></code></a> or <a class="reference internal" href="#c.PyMem_RawCalloc" title="PyMem_RawCalloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawCalloc()</span></code></a>.</p> <p>If the request fails, <a class="reference internal" href="#c.PyMem_RawRealloc" title="PyMem_RawRealloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawRealloc()</span></code></a> returns <code class="docutils literal notranslate"><span class="pre">NULL</span></code> and <em>p</em> remains a valid pointer to the previous memory area.</p> </dd></dl> <dl class="function"> <dt id="c.PyMem_RawFree"> void <code class="sig-name descname">PyMem_RawFree</code><span class="sig-paren">(</span>void<em> *p</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_RawFree" title="Permalink to this definition">¶</a></dt> <dd><p>Frees the memory block pointed to by <em>p</em>, which must have been returned by a previous call to <a class="reference internal" href="#c.PyMem_RawMalloc" title="PyMem_RawMalloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawMalloc()</span></code></a>, <a class="reference internal" href="#c.PyMem_RawRealloc" title="PyMem_RawRealloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawRealloc()</span></code></a> or <a class="reference internal" href="#c.PyMem_RawCalloc" title="PyMem_RawCalloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawCalloc()</span></code></a>. Otherwise, or if <code class="docutils literal notranslate"><span class="pre">PyMem_RawFree(p)</span></code> has been called before, undefined behavior occurs.</p> <p>If <em>p</em> is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, no operation is performed.</p> </dd></dl> </div> <div class="section" id="memory-interface"> <span id="memoryinterface"></span><h2>Memory Interface<a class="headerlink" href="#memory-interface" title="Permalink to this headline">¶</a></h2> <p>The following function sets, modeled after the ANSI C standard, but specifying behavior when requesting zero bytes, are available for allocating and releasing memory from the Python heap.</p> <p>The <a class="reference internal" href="#default-memory-allocators"><span class="std std-ref">default memory allocator</span></a> uses the <a class="reference internal" href="#pymalloc"><span class="std std-ref">pymalloc memory allocator</span></a>.</p> <div class="admonition warning"> <p class="admonition-title">Warning</p> <p>The <a class="reference internal" href="../glossary.html#term-global-interpreter-lock"><span class="xref std std-term">GIL</span></a> must be held when using these functions.</p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.6: </span>The default allocator is now pymalloc instead of system <code class="xref c c-func docutils literal notranslate"><span class="pre">malloc()</span></code>.</p> </div> <dl class="function"> <dt id="c.PyMem_Malloc"> void* <code class="sig-name descname">PyMem_Malloc</code><span class="sig-paren">(</span>size_t<em> n</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_Malloc" title="Permalink to this definition">¶</a></dt> <dd><p>Allocates <em>n</em> bytes and returns a pointer of type <code class="xref c c-type docutils literal notranslate"><span class="pre">void*</span></code> to the allocated memory, or <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if the request fails.</p> <p>Requesting zero bytes returns a distinct non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code> pointer if possible, as if <code class="docutils literal notranslate"><span class="pre">PyMem_Malloc(1)</span></code> had been called instead. The memory will not have been initialized in any way.</p> </dd></dl> <dl class="function"> <dt id="c.PyMem_Calloc"> void* <code class="sig-name descname">PyMem_Calloc</code><span class="sig-paren">(</span>size_t<em> nelem</em>, size_t<em> elsize</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_Calloc" title="Permalink to this definition">¶</a></dt> <dd><p>Allocates <em>nelem</em> elements each whose size in bytes is <em>elsize</em> and returns a pointer of type <code class="xref c c-type docutils literal notranslate"><span class="pre">void*</span></code> to the allocated memory, or <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if the request fails. The memory is initialized to zeros.</p> <p>Requesting zero elements or elements of size zero bytes returns a distinct non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code> pointer if possible, as if <code class="docutils literal notranslate"><span class="pre">PyMem_Calloc(1,</span> <span class="pre">1)</span></code> had been called instead.</p> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.5.</span></p> </div> </dd></dl> <dl class="function"> <dt id="c.PyMem_Realloc"> void* <code class="sig-name descname">PyMem_Realloc</code><span class="sig-paren">(</span>void<em> *p</em>, size_t<em> n</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_Realloc" title="Permalink to this definition">¶</a></dt> <dd><p>Resizes the memory block pointed to by <em>p</em> to <em>n</em> bytes. The contents will be unchanged to the minimum of the old and the new sizes.</p> <p>If <em>p</em> is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, the call is equivalent to <code class="docutils literal notranslate"><span class="pre">PyMem_Malloc(n)</span></code>; else if <em>n</em> is equal to zero, the memory block is resized but is not freed, and the returned pointer is non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p> <p>Unless <em>p</em> is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, it must have been returned by a previous call to <a class="reference internal" href="#c.PyMem_Malloc" title="PyMem_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Malloc()</span></code></a>, <a class="reference internal" href="#c.PyMem_Realloc" title="PyMem_Realloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Realloc()</span></code></a> or <a class="reference internal" href="#c.PyMem_Calloc" title="PyMem_Calloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Calloc()</span></code></a>.</p> <p>If the request fails, <a class="reference internal" href="#c.PyMem_Realloc" title="PyMem_Realloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Realloc()</span></code></a> returns <code class="docutils literal notranslate"><span class="pre">NULL</span></code> and <em>p</em> remains a valid pointer to the previous memory area.</p> </dd></dl> <dl class="function"> <dt id="c.PyMem_Free"> void <code class="sig-name descname">PyMem_Free</code><span class="sig-paren">(</span>void<em> *p</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_Free" title="Permalink to this definition">¶</a></dt> <dd><p>Frees the memory block pointed to by <em>p</em>, which must have been returned by a previous call to <a class="reference internal" href="#c.PyMem_Malloc" title="PyMem_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Malloc()</span></code></a>, <a class="reference internal" href="#c.PyMem_Realloc" title="PyMem_Realloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Realloc()</span></code></a> or <a class="reference internal" href="#c.PyMem_Calloc" title="PyMem_Calloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Calloc()</span></code></a>. Otherwise, or if <code class="docutils literal notranslate"><span class="pre">PyMem_Free(p)</span></code> has been called before, undefined behavior occurs.</p> <p>If <em>p</em> is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, no operation is performed.</p> </dd></dl> <p>The following type-oriented macros are provided for convenience. Note that <em>TYPE</em> refers to any C type.</p> <dl class="function"> <dt id="c.PyMem_New"> TYPE* <code class="sig-name descname">PyMem_New</code><span class="sig-paren">(</span>TYPE, size_t<em> n</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_New" title="Permalink to this definition">¶</a></dt> <dd><p>Same as <a class="reference internal" href="#c.PyMem_Malloc" title="PyMem_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Malloc()</span></code></a>, but allocates <code class="docutils literal notranslate"><span class="pre">(n</span> <span class="pre">*</span> <span class="pre">sizeof(TYPE))</span></code> bytes of memory. Returns a pointer cast to <code class="xref c c-type docutils literal notranslate"><span class="pre">TYPE*</span></code>. The memory will not have been initialized in any way.</p> </dd></dl> <dl class="function"> <dt id="c.PyMem_Resize"> TYPE* <code class="sig-name descname">PyMem_Resize</code><span class="sig-paren">(</span>void<em> *p</em>, TYPE, size_t<em> n</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_Resize" title="Permalink to this definition">¶</a></dt> <dd><p>Same as <a class="reference internal" href="#c.PyMem_Realloc" title="PyMem_Realloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Realloc()</span></code></a>, but the memory block is resized to <code class="docutils literal notranslate"><span class="pre">(n</span> <span class="pre">*</span> <span class="pre">sizeof(TYPE))</span></code> bytes. Returns a pointer cast to <code class="xref c c-type docutils literal notranslate"><span class="pre">TYPE*</span></code>. On return, <em>p</em> will be a pointer to the new memory area, or <code class="docutils literal notranslate"><span class="pre">NULL</span></code> in the event of failure.</p> <p>This is a C preprocessor macro; <em>p</em> is always reassigned. Save the original value of <em>p</em> to avoid losing memory when handling errors.</p> </dd></dl> <dl class="function"> <dt id="c.PyMem_Del"> void <code class="sig-name descname">PyMem_Del</code><span class="sig-paren">(</span>void<em> *p</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_Del" title="Permalink to this definition">¶</a></dt> <dd><p>Same as <a class="reference internal" href="#c.PyMem_Free" title="PyMem_Free"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Free()</span></code></a>.</p> </dd></dl> <p>In addition, the following macro sets are provided for calling the Python memory allocator directly, without involving the C API functions listed above. However, note that their use does not preserve binary compatibility across Python versions and is therefore deprecated in extension modules.</p> <ul class="simple"> <li><p><code class="docutils literal notranslate"><span class="pre">PyMem_MALLOC(size)</span></code></p></li> <li><p><code class="docutils literal notranslate"><span class="pre">PyMem_NEW(type,</span> <span class="pre">size)</span></code></p></li> <li><p><code class="docutils literal notranslate"><span class="pre">PyMem_REALLOC(ptr,</span> <span class="pre">size)</span></code></p></li> <li><p><code class="docutils literal notranslate"><span class="pre">PyMem_RESIZE(ptr,</span> <span class="pre">type,</span> <span class="pre">size)</span></code></p></li> <li><p><code class="docutils literal notranslate"><span class="pre">PyMem_FREE(ptr)</span></code></p></li> <li><p><code class="docutils literal notranslate"><span class="pre">PyMem_DEL(ptr)</span></code></p></li> </ul> </div> <div class="section" id="object-allocators"> <h2>Object allocators<a class="headerlink" href="#object-allocators" title="Permalink to this headline">¶</a></h2> <p>The following function sets, modeled after the ANSI C standard, but specifying behavior when requesting zero bytes, are available for allocating and releasing memory from the Python heap.</p> <p>The <a class="reference internal" href="#default-memory-allocators"><span class="std std-ref">default object allocator</span></a> uses the <a class="reference internal" href="#pymalloc"><span class="std std-ref">pymalloc memory allocator</span></a>.</p> <div class="admonition warning"> <p class="admonition-title">Warning</p> <p>The <a class="reference internal" href="../glossary.html#term-global-interpreter-lock"><span class="xref std std-term">GIL</span></a> must be held when using these functions.</p> </div> <dl class="function"> <dt id="c.PyObject_Malloc"> void* <code class="sig-name descname">PyObject_Malloc</code><span class="sig-paren">(</span>size_t<em> n</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyObject_Malloc" title="Permalink to this definition">¶</a></dt> <dd><p>Allocates <em>n</em> bytes and returns a pointer of type <code class="xref c c-type docutils literal notranslate"><span class="pre">void*</span></code> to the allocated memory, or <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if the request fails.</p> <p>Requesting zero bytes returns a distinct non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code> pointer if possible, as if <code class="docutils literal notranslate"><span class="pre">PyObject_Malloc(1)</span></code> had been called instead. The memory will not have been initialized in any way.</p> </dd></dl> <dl class="function"> <dt id="c.PyObject_Calloc"> void* <code class="sig-name descname">PyObject_Calloc</code><span class="sig-paren">(</span>size_t<em> nelem</em>, size_t<em> elsize</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyObject_Calloc" title="Permalink to this definition">¶</a></dt> <dd><p>Allocates <em>nelem</em> elements each whose size in bytes is <em>elsize</em> and returns a pointer of type <code class="xref c c-type docutils literal notranslate"><span class="pre">void*</span></code> to the allocated memory, or <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if the request fails. The memory is initialized to zeros.</p> <p>Requesting zero elements or elements of size zero bytes returns a distinct non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code> pointer if possible, as if <code class="docutils literal notranslate"><span class="pre">PyObject_Calloc(1,</span> <span class="pre">1)</span></code> had been called instead.</p> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.5.</span></p> </div> </dd></dl> <dl class="function"> <dt id="c.PyObject_Realloc"> void* <code class="sig-name descname">PyObject_Realloc</code><span class="sig-paren">(</span>void<em> *p</em>, size_t<em> n</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyObject_Realloc" title="Permalink to this definition">¶</a></dt> <dd><p>Resizes the memory block pointed to by <em>p</em> to <em>n</em> bytes. The contents will be unchanged to the minimum of the old and the new sizes.</p> <p>If <em>p</em> is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, the call is equivalent to <code class="docutils literal notranslate"><span class="pre">PyObject_Malloc(n)</span></code>; else if <em>n</em> is equal to zero, the memory block is resized but is not freed, and the returned pointer is non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p> <p>Unless <em>p</em> is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, it must have been returned by a previous call to <a class="reference internal" href="#c.PyObject_Malloc" title="PyObject_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Malloc()</span></code></a>, <a class="reference internal" href="#c.PyObject_Realloc" title="PyObject_Realloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Realloc()</span></code></a> or <a class="reference internal" href="#c.PyObject_Calloc" title="PyObject_Calloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Calloc()</span></code></a>.</p> <p>If the request fails, <a class="reference internal" href="#c.PyObject_Realloc" title="PyObject_Realloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Realloc()</span></code></a> returns <code class="docutils literal notranslate"><span class="pre">NULL</span></code> and <em>p</em> remains a valid pointer to the previous memory area.</p> </dd></dl> <dl class="function"> <dt id="c.PyObject_Free"> void <code class="sig-name descname">PyObject_Free</code><span class="sig-paren">(</span>void<em> *p</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyObject_Free" title="Permalink to this definition">¶</a></dt> <dd><p>Frees the memory block pointed to by <em>p</em>, which must have been returned by a previous call to <a class="reference internal" href="#c.PyObject_Malloc" title="PyObject_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Malloc()</span></code></a>, <a class="reference internal" href="#c.PyObject_Realloc" title="PyObject_Realloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Realloc()</span></code></a> or <a class="reference internal" href="#c.PyObject_Calloc" title="PyObject_Calloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Calloc()</span></code></a>. Otherwise, or if <code class="docutils literal notranslate"><span class="pre">PyObject_Free(p)</span></code> has been called before, undefined behavior occurs.</p> <p>If <em>p</em> is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, no operation is performed.</p> </dd></dl> </div> <div class="section" id="default-memory-allocators"> <span id="id1"></span><h2>Default Memory Allocators<a class="headerlink" href="#default-memory-allocators" title="Permalink to this headline">¶</a></h2> <p>Default memory allocators:</p> <table class="docutils align-default"> <colgroup> <col style="width: 28%" /> <col style="width: 18%" /> <col style="width: 16%" /> <col style="width: 19%" /> <col style="width: 18%" /> </colgroup> <thead> <tr class="row-odd"><th class="head"><p>Configuration</p></th> <th class="head"><p>Name</p></th> <th class="head"><p>PyMem_RawMalloc</p></th> <th class="head"><p>PyMem_Malloc</p></th> <th class="head"><p>PyObject_Malloc</p></th> </tr> </thead> <tbody> <tr class="row-even"><td><p>Release build</p></td> <td><p><code class="docutils literal notranslate"><span class="pre">"pymalloc"</span></code></p></td> <td><p><code class="docutils literal notranslate"><span class="pre">malloc</span></code></p></td> <td><p><code class="docutils literal notranslate"><span class="pre">pymalloc</span></code></p></td> <td><p><code class="docutils literal notranslate"><span class="pre">pymalloc</span></code></p></td> </tr> <tr class="row-odd"><td><p>Debug build</p></td> <td><p><code class="docutils literal notranslate"><span class="pre">"pymalloc_debug"</span></code></p></td> <td><p><code class="docutils literal notranslate"><span class="pre">malloc</span></code> + debug</p></td> <td><p><code class="docutils literal notranslate"><span class="pre">pymalloc</span></code> + debug</p></td> <td><p><code class="docutils literal notranslate"><span class="pre">pymalloc</span></code> + debug</p></td> </tr> <tr class="row-even"><td><p>Release build, without pymalloc</p></td> <td><p><code class="docutils literal notranslate"><span class="pre">"malloc"</span></code></p></td> <td><p><code class="docutils literal notranslate"><span class="pre">malloc</span></code></p></td> <td><p><code class="docutils literal notranslate"><span class="pre">malloc</span></code></p></td> <td><p><code class="docutils literal notranslate"><span class="pre">malloc</span></code></p></td> </tr> <tr class="row-odd"><td><p>Debug build, without pymalloc</p></td> <td><p><code class="docutils literal notranslate"><span class="pre">"malloc_debug"</span></code></p></td> <td><p><code class="docutils literal notranslate"><span class="pre">malloc</span></code> + debug</p></td> <td><p><code class="docutils literal notranslate"><span class="pre">malloc</span></code> + debug</p></td> <td><p><code class="docutils literal notranslate"><span class="pre">malloc</span></code> + debug</p></td> </tr> </tbody> </table> <p>Legend:</p> <ul class="simple"> <li><p>Name: value for <span class="target" id="index-3"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONMALLOC"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONMALLOC</span></code></a> environment variable</p></li> <li><p><code class="docutils literal notranslate"><span class="pre">malloc</span></code>: system allocators from the standard C library, C functions: <code class="xref c c-func docutils literal notranslate"><span class="pre">malloc()</span></code>, <code class="xref c c-func docutils literal notranslate"><span class="pre">calloc()</span></code>, <code class="xref c c-func docutils literal notranslate"><span class="pre">realloc()</span></code> and <code class="xref c c-func docutils literal notranslate"><span class="pre">free()</span></code></p></li> <li><p><code class="docutils literal notranslate"><span class="pre">pymalloc</span></code>: <a class="reference internal" href="#pymalloc"><span class="std std-ref">pymalloc memory allocator</span></a></p></li> <li><p>“+ debug”: with debug hooks installed by <a class="reference internal" href="#c.PyMem_SetupDebugHooks" title="PyMem_SetupDebugHooks"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_SetupDebugHooks()</span></code></a></p></li> </ul> </div> <div class="section" id="customize-memory-allocators"> <h2>Customize Memory Allocators<a class="headerlink" href="#customize-memory-allocators" title="Permalink to this headline">¶</a></h2> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.4.</span></p> </div> <dl class="type"> <dt id="c.PyMemAllocatorEx"> <code class="sig-name descname">PyMemAllocatorEx</code><a class="headerlink" href="#c.PyMemAllocatorEx" title="Permalink to this definition">¶</a></dt> <dd><p>Structure used to describe a memory block allocator. The structure has four fields:</p> <table class="docutils align-default"> <colgroup> <col style="width: 60%" /> <col style="width: 40%" /> </colgroup> <thead> <tr class="row-odd"><th class="head"><p>Field</p></th> <th class="head"><p>Meaning</p></th> </tr> </thead> <tbody> <tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">void</span> <span class="pre">*ctx</span></code></p></td> <td><p>user context passed as first argument</p></td> </tr> <tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">void*</span> <span class="pre">malloc(void</span> <span class="pre">*ctx,</span> <span class="pre">size_t</span> <span class="pre">size)</span></code></p></td> <td><p>allocate a memory block</p></td> </tr> <tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">void*</span> <span class="pre">calloc(void</span> <span class="pre">*ctx,</span> <span class="pre">size_t</span> <span class="pre">nelem,</span> <span class="pre">size_t</span> <span class="pre">elsize)</span></code></p></td> <td><p>allocate a memory block initialized with zeros</p></td> </tr> <tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">void*</span> <span class="pre">realloc(void</span> <span class="pre">*ctx,</span> <span class="pre">void</span> <span class="pre">*ptr,</span> <span class="pre">size_t</span> <span class="pre">new_size)</span></code></p></td> <td><p>allocate or resize a memory block</p></td> </tr> <tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">void</span> <span class="pre">free(void</span> <span class="pre">*ctx,</span> <span class="pre">void</span> <span class="pre">*ptr)</span></code></p></td> <td><p>free a memory block</p></td> </tr> </tbody> </table> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.5: </span>The <code class="xref c c-type docutils literal notranslate"><span class="pre">PyMemAllocator</span></code> structure was renamed to <a class="reference internal" href="#c.PyMemAllocatorEx" title="PyMemAllocatorEx"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyMemAllocatorEx</span></code></a> and a new <code class="docutils literal notranslate"><span class="pre">calloc</span></code> field was added.</p> </div> </dd></dl> <dl class="type"> <dt id="c.PyMemAllocatorDomain"> <code class="sig-name descname">PyMemAllocatorDomain</code><a class="headerlink" href="#c.PyMemAllocatorDomain" title="Permalink to this definition">¶</a></dt> <dd><p>Enum used to identify an allocator domain. Domains:</p> <dl class="var"> <dt id="c.PYMEM_DOMAIN_RAW"> <code class="sig-name descname">PYMEM_DOMAIN_RAW</code><a class="headerlink" href="#c.PYMEM_DOMAIN_RAW" title="Permalink to this definition">¶</a></dt> <dd><p>Functions:</p> <ul class="simple"> <li><p><a class="reference internal" href="#c.PyMem_RawMalloc" title="PyMem_RawMalloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawMalloc()</span></code></a></p></li> <li><p><a class="reference internal" href="#c.PyMem_RawRealloc" title="PyMem_RawRealloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawRealloc()</span></code></a></p></li> <li><p><a class="reference internal" href="#c.PyMem_RawCalloc" title="PyMem_RawCalloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawCalloc()</span></code></a></p></li> <li><p><a class="reference internal" href="#c.PyMem_RawFree" title="PyMem_RawFree"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawFree()</span></code></a></p></li> </ul> </dd></dl> <dl class="var"> <dt id="c.PYMEM_DOMAIN_MEM"> <code class="sig-name descname">PYMEM_DOMAIN_MEM</code><a class="headerlink" href="#c.PYMEM_DOMAIN_MEM" title="Permalink to this definition">¶</a></dt> <dd><p>Functions:</p> <ul class="simple"> <li><p><a class="reference internal" href="#c.PyMem_Malloc" title="PyMem_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Malloc()</span></code></a>,</p></li> <li><p><a class="reference internal" href="#c.PyMem_Realloc" title="PyMem_Realloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Realloc()</span></code></a></p></li> <li><p><a class="reference internal" href="#c.PyMem_Calloc" title="PyMem_Calloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Calloc()</span></code></a></p></li> <li><p><a class="reference internal" href="#c.PyMem_Free" title="PyMem_Free"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Free()</span></code></a></p></li> </ul> </dd></dl> <dl class="var"> <dt id="c.PYMEM_DOMAIN_OBJ"> <code class="sig-name descname">PYMEM_DOMAIN_OBJ</code><a class="headerlink" href="#c.PYMEM_DOMAIN_OBJ" title="Permalink to this definition">¶</a></dt> <dd><p>Functions:</p> <ul class="simple"> <li><p><a class="reference internal" href="#c.PyObject_Malloc" title="PyObject_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Malloc()</span></code></a></p></li> <li><p><a class="reference internal" href="#c.PyObject_Realloc" title="PyObject_Realloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Realloc()</span></code></a></p></li> <li><p><a class="reference internal" href="#c.PyObject_Calloc" title="PyObject_Calloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Calloc()</span></code></a></p></li> <li><p><a class="reference internal" href="#c.PyObject_Free" title="PyObject_Free"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Free()</span></code></a></p></li> </ul> </dd></dl> </dd></dl> <dl class="function"> <dt id="c.PyMem_GetAllocator"> void <code class="sig-name descname">PyMem_GetAllocator</code><span class="sig-paren">(</span><a class="reference internal" href="#c.PyMemAllocatorDomain" title="PyMemAllocatorDomain">PyMemAllocatorDomain</a><em> domain</em>, <a class="reference internal" href="#c.PyMemAllocatorEx" title="PyMemAllocatorEx">PyMemAllocatorEx</a><em> *allocator</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_GetAllocator" title="Permalink to this definition">¶</a></dt> <dd><p>Get the memory block allocator of the specified domain.</p> </dd></dl> <dl class="function"> <dt id="c.PyMem_SetAllocator"> void <code class="sig-name descname">PyMem_SetAllocator</code><span class="sig-paren">(</span><a class="reference internal" href="#c.PyMemAllocatorDomain" title="PyMemAllocatorDomain">PyMemAllocatorDomain</a><em> domain</em>, <a class="reference internal" href="#c.PyMemAllocatorEx" title="PyMemAllocatorEx">PyMemAllocatorEx</a><em> *allocator</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_SetAllocator" title="Permalink to this definition">¶</a></dt> <dd><p>Set the memory block allocator of the specified domain.</p> <p>The new allocator must return a distinct non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code> pointer when requesting zero bytes.</p> <p>For the <a class="reference internal" href="#c.PYMEM_DOMAIN_RAW" title="PYMEM_DOMAIN_RAW"><code class="xref c c-data docutils literal notranslate"><span class="pre">PYMEM_DOMAIN_RAW</span></code></a> domain, the allocator must be thread-safe: the <a class="reference internal" href="../glossary.html#term-global-interpreter-lock"><span class="xref std std-term">GIL</span></a> is not held when the allocator is called.</p> <p>If the new allocator is not a hook (does not call the previous allocator), the <a class="reference internal" href="#c.PyMem_SetupDebugHooks" title="PyMem_SetupDebugHooks"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_SetupDebugHooks()</span></code></a> function must be called to reinstall the debug hooks on top on the new allocator.</p> </dd></dl> <dl class="function"> <dt id="c.PyMem_SetupDebugHooks"> void <code class="sig-name descname">PyMem_SetupDebugHooks</code><span class="sig-paren">(</span>void<span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_SetupDebugHooks" title="Permalink to this definition">¶</a></dt> <dd><p>Setup hooks to detect bugs in the Python memory allocator functions.</p> <p>Newly allocated memory is filled with the byte <code class="docutils literal notranslate"><span class="pre">0xCD</span></code> (<code class="docutils literal notranslate"><span class="pre">CLEANBYTE</span></code>), freed memory is filled with the byte <code class="docutils literal notranslate"><span class="pre">0xDD</span></code> (<code class="docutils literal notranslate"><span class="pre">DEADBYTE</span></code>). Memory blocks are surrounded by “forbidden bytes” (<code class="docutils literal notranslate"><span class="pre">FORBIDDENBYTE</span></code>: byte <code class="docutils literal notranslate"><span class="pre">0xFD</span></code>).</p> <p>Runtime checks:</p> <ul class="simple"> <li><p>Detect API violations, ex: <a class="reference internal" href="#c.PyObject_Free" title="PyObject_Free"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Free()</span></code></a> called on a buffer allocated by <a class="reference internal" href="#c.PyMem_Malloc" title="PyMem_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Malloc()</span></code></a></p></li> <li><p>Detect write before the start of the buffer (buffer underflow)</p></li> <li><p>Detect write after the end of the buffer (buffer overflow)</p></li> <li><p>Check that the <a class="reference internal" href="../glossary.html#term-global-interpreter-lock"><span class="xref std std-term">GIL</span></a> is held when allocator functions of <a class="reference internal" href="#c.PYMEM_DOMAIN_OBJ" title="PYMEM_DOMAIN_OBJ"><code class="xref c c-data docutils literal notranslate"><span class="pre">PYMEM_DOMAIN_OBJ</span></code></a> (ex: <a class="reference internal" href="#c.PyObject_Malloc" title="PyObject_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Malloc()</span></code></a>) and <a class="reference internal" href="#c.PYMEM_DOMAIN_MEM" title="PYMEM_DOMAIN_MEM"><code class="xref c c-data docutils literal notranslate"><span class="pre">PYMEM_DOMAIN_MEM</span></code></a> (ex: <a class="reference internal" href="#c.PyMem_Malloc" title="PyMem_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Malloc()</span></code></a>) domains are called</p></li> </ul> <p>On error, the debug hooks use the <a class="reference internal" href="../library/tracemalloc.html#module-tracemalloc" title="tracemalloc: Trace memory allocations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">tracemalloc</span></code></a> module to get the traceback where a memory block was allocated. The traceback is only displayed if <a class="reference internal" href="../library/tracemalloc.html#module-tracemalloc" title="tracemalloc: Trace memory allocations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">tracemalloc</span></code></a> is tracing Python memory allocations and the memory block was traced.</p> <p>These hooks are <a class="reference internal" href="#default-memory-allocators"><span class="std std-ref">installed by default</span></a> if Python is compiled in debug mode. The <span class="target" id="index-4"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONMALLOC"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONMALLOC</span></code></a> environment variable can be used to install debug hooks on a Python compiled in release mode.</p> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.6: </span>This function now also works on Python compiled in release mode. On error, the debug hooks now use <a class="reference internal" href="../library/tracemalloc.html#module-tracemalloc" title="tracemalloc: Trace memory allocations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">tracemalloc</span></code></a> to get the traceback where a memory block was allocated. The debug hooks now also check if the GIL is held when functions of <a class="reference internal" href="#c.PYMEM_DOMAIN_OBJ" title="PYMEM_DOMAIN_OBJ"><code class="xref c c-data docutils literal notranslate"><span class="pre">PYMEM_DOMAIN_OBJ</span></code></a> and <a class="reference internal" href="#c.PYMEM_DOMAIN_MEM" title="PYMEM_DOMAIN_MEM"><code class="xref c c-data docutils literal notranslate"><span class="pre">PYMEM_DOMAIN_MEM</span></code></a> domains are called.</p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.7.3: </span>Byte patterns <code class="docutils literal notranslate"><span class="pre">0xCB</span></code> (<code class="docutils literal notranslate"><span class="pre">CLEANBYTE</span></code>), <code class="docutils literal notranslate"><span class="pre">0xDB</span></code> (<code class="docutils literal notranslate"><span class="pre">DEADBYTE</span></code>) and <code class="docutils literal notranslate"><span class="pre">0xFB</span></code> (<code class="docutils literal notranslate"><span class="pre">FORBIDDENBYTE</span></code>) have been replaced with <code class="docutils literal notranslate"><span class="pre">0xCD</span></code>, <code class="docutils literal notranslate"><span class="pre">0xDD</span></code> and <code class="docutils literal notranslate"><span class="pre">0xFD</span></code> to use the same values than Windows CRT debug <code class="docutils literal notranslate"><span class="pre">malloc()</span></code> and <code class="docutils literal notranslate"><span class="pre">free()</span></code>.</p> </div> </dd></dl> </div> <div class="section" id="the-pymalloc-allocator"> <span id="pymalloc"></span><h2>The pymalloc allocator<a class="headerlink" href="#the-pymalloc-allocator" title="Permalink to this headline">¶</a></h2> <p>Python has a <em>pymalloc</em> allocator optimized for small objects (smaller or equal to 512 bytes) with a short lifetime. It uses memory mappings called “arenas” with a fixed size of 256 KiB. It falls back to <a class="reference internal" href="#c.PyMem_RawMalloc" title="PyMem_RawMalloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawMalloc()</span></code></a> and <a class="reference internal" href="#c.PyMem_RawRealloc" title="PyMem_RawRealloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawRealloc()</span></code></a> for allocations larger than 512 bytes.</p> <p><em>pymalloc</em> is the <a class="reference internal" href="#default-memory-allocators"><span class="std std-ref">default allocator</span></a> of the <a class="reference internal" href="#c.PYMEM_DOMAIN_MEM" title="PYMEM_DOMAIN_MEM"><code class="xref c c-data docutils literal notranslate"><span class="pre">PYMEM_DOMAIN_MEM</span></code></a> (ex: <a class="reference internal" href="#c.PyMem_Malloc" title="PyMem_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Malloc()</span></code></a>) and <a class="reference internal" href="#c.PYMEM_DOMAIN_OBJ" title="PYMEM_DOMAIN_OBJ"><code class="xref c c-data docutils literal notranslate"><span class="pre">PYMEM_DOMAIN_OBJ</span></code></a> (ex: <a class="reference internal" href="#c.PyObject_Malloc" title="PyObject_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Malloc()</span></code></a>) domains.</p> <p>The arena allocator uses the following functions:</p> <ul class="simple"> <li><p><code class="xref c c-func docutils literal notranslate"><span class="pre">VirtualAlloc()</span></code> and <code class="xref c c-func docutils literal notranslate"><span class="pre">VirtualFree()</span></code> on Windows,</p></li> <li><p><code class="xref c c-func docutils literal notranslate"><span class="pre">mmap()</span></code> and <code class="xref c c-func docutils literal notranslate"><span class="pre">munmap()</span></code> if available,</p></li> <li><p><code class="xref c c-func docutils literal notranslate"><span class="pre">malloc()</span></code> and <code class="xref c c-func docutils literal notranslate"><span class="pre">free()</span></code> otherwise.</p></li> </ul> <div class="section" id="customize-pymalloc-arena-allocator"> <h3>Customize pymalloc Arena Allocator<a class="headerlink" href="#customize-pymalloc-arena-allocator" title="Permalink to this headline">¶</a></h3> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.4.</span></p> </div> <dl class="type"> <dt id="c.PyObjectArenaAllocator"> <code class="sig-name descname">PyObjectArenaAllocator</code><a class="headerlink" href="#c.PyObjectArenaAllocator" title="Permalink to this definition">¶</a></dt> <dd><p>Structure used to describe an arena allocator. The structure has three fields:</p> <table class="docutils align-default"> <colgroup> <col style="width: 56%" /> <col style="width: 44%" /> </colgroup> <thead> <tr class="row-odd"><th class="head"><p>Field</p></th> <th class="head"><p>Meaning</p></th> </tr> </thead> <tbody> <tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">void</span> <span class="pre">*ctx</span></code></p></td> <td><p>user context passed as first argument</p></td> </tr> <tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">void*</span> <span class="pre">alloc(void</span> <span class="pre">*ctx,</span> <span class="pre">size_t</span> <span class="pre">size)</span></code></p></td> <td><p>allocate an arena of size bytes</p></td> </tr> <tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">void</span> <span class="pre">free(void</span> <span class="pre">*ctx,</span> <span class="pre">size_t</span> <span class="pre">size,</span> <span class="pre">void</span> <span class="pre">*ptr)</span></code></p></td> <td><p>free an arena</p></td> </tr> </tbody> </table> </dd></dl> <dl class="function"> <dt id="c.PyObject_GetArenaAllocator"> <code class="sig-name descname">PyObject_GetArenaAllocator</code><span class="sig-paren">(</span><a class="reference internal" href="#c.PyObjectArenaAllocator" title="PyObjectArenaAllocator">PyObjectArenaAllocator</a><em> *allocator</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyObject_GetArenaAllocator" title="Permalink to this definition">¶</a></dt> <dd><p>Get the arena allocator.</p> </dd></dl> <dl class="function"> <dt id="c.PyObject_SetArenaAllocator"> <code class="sig-name descname">PyObject_SetArenaAllocator</code><span class="sig-paren">(</span><a class="reference internal" href="#c.PyObjectArenaAllocator" title="PyObjectArenaAllocator">PyObjectArenaAllocator</a><em> *allocator</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyObject_SetArenaAllocator" title="Permalink to this definition">¶</a></dt> <dd><p>Set the arena allocator.</p> </dd></dl> </div> </div> <div class="section" id="tracemalloc-c-api"> <h2>tracemalloc C API<a class="headerlink" href="#tracemalloc-c-api" title="Permalink to this headline">¶</a></h2> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.7.</span></p> </div> <dl class="function"> <dt id="c.PyTraceMalloc_Track"> int <code class="sig-name descname">PyTraceMalloc_Track</code><span class="sig-paren">(</span>unsigned int<em> domain</em>, uintptr_t<em> ptr</em>, size_t<em> size</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyTraceMalloc_Track" title="Permalink to this definition">¶</a></dt> <dd><p>Track an allocated memory block in the <a class="reference internal" href="../library/tracemalloc.html#module-tracemalloc" title="tracemalloc: Trace memory allocations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">tracemalloc</span></code></a> module.</p> <p>Return <code class="docutils literal notranslate"><span class="pre">0</span></code> on success, return <code class="docutils literal notranslate"><span class="pre">-1</span></code> on error (failed to allocate memory to store the trace). Return <code class="docutils literal notranslate"><span class="pre">-2</span></code> if tracemalloc is disabled.</p> <p>If memory block is already tracked, update the existing trace.</p> </dd></dl> <dl class="function"> <dt id="c.PyTraceMalloc_Untrack"> int <code class="sig-name descname">PyTraceMalloc_Untrack</code><span class="sig-paren">(</span>unsigned int<em> domain</em>, uintptr_t<em> ptr</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyTraceMalloc_Untrack" title="Permalink to this definition">¶</a></dt> <dd><p>Untrack an allocated memory block in the <a class="reference internal" href="../library/tracemalloc.html#module-tracemalloc" title="tracemalloc: Trace memory allocations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">tracemalloc</span></code></a> module. Do nothing if the block was not tracked.</p> <p>Return <code class="docutils literal notranslate"><span class="pre">-2</span></code> if tracemalloc is disabled, otherwise return <code class="docutils literal notranslate"><span class="pre">0</span></code>.</p> </dd></dl> </div> <div class="section" id="examples"> <span id="memoryexamples"></span><h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2> <p>Here is the example from section <a class="reference internal" href="#memoryoverview"><span class="std std-ref">Overview</span></a>, rewritten so that the I/O buffer is allocated from the Python heap by using the first function set:</p> <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">PyObject</span> <span class="o">*</span><span class="n">res</span><span class="p">;</span> <span class="kt">char</span> <span class="o">*</span><span class="n">buf</span> <span class="o">=</span> <span class="p">(</span><span class="kt">char</span> <span class="o">*</span><span class="p">)</span> <span class="n">PyMem_Malloc</span><span class="p">(</span><span class="n">BUFSIZ</span><span class="p">);</span> <span class="cm">/* for I/O */</span> <span class="k">if</span> <span class="p">(</span><span class="n">buf</span> <span class="o">==</span> <span class="nb">NULL</span><span class="p">)</span> <span class="k">return</span> <span class="n">PyErr_NoMemory</span><span class="p">();</span> <span class="cm">/* ...Do some I/O operation involving buf... */</span> <span class="n">res</span> <span class="o">=</span> <span class="n">PyBytes_FromString</span><span class="p">(</span><span class="n">buf</span><span class="p">);</span> <span class="n">PyMem_Free</span><span class="p">(</span><span class="n">buf</span><span class="p">);</span> <span class="cm">/* allocated with PyMem_Malloc */</span> <span class="k">return</span> <span class="n">res</span><span class="p">;</span> </pre></div> </div> <p>The same code using the type-oriented function set:</p> <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">PyObject</span> <span class="o">*</span><span class="n">res</span><span class="p">;</span> <span class="kt">char</span> <span class="o">*</span><span class="n">buf</span> <span class="o">=</span> <span class="n">PyMem_New</span><span class="p">(</span><span class="kt">char</span><span class="p">,</span> <span class="n">BUFSIZ</span><span class="p">);</span> <span class="cm">/* for I/O */</span> <span class="k">if</span> <span class="p">(</span><span class="n">buf</span> <span class="o">==</span> <span class="nb">NULL</span><span class="p">)</span> <span class="k">return</span> <span class="n">PyErr_NoMemory</span><span class="p">();</span> <span class="cm">/* ...Do some I/O operation involving buf... */</span> <span class="n">res</span> <span class="o">=</span> <span class="n">PyBytes_FromString</span><span class="p">(</span><span class="n">buf</span><span class="p">);</span> <span class="n">PyMem_Del</span><span class="p">(</span><span class="n">buf</span><span class="p">);</span> <span class="cm">/* allocated with PyMem_New */</span> <span class="k">return</span> <span class="n">res</span><span class="p">;</span> </pre></div> </div> <p>Note that in the two examples above, the buffer is always manipulated via functions belonging to the same set. Indeed, it is required to use the same memory API family for a given memory block, so that the risk of mixing different allocators is reduced to a minimum. The following code sequence contains two errors, one of which is labeled as <em>fatal</em> because it mixes two different allocators operating on different heaps.</p> <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="kt">char</span> <span class="o">*</span><span class="n">buf1</span> <span class="o">=</span> <span class="n">PyMem_New</span><span class="p">(</span><span class="kt">char</span><span class="p">,</span> <span class="n">BUFSIZ</span><span class="p">);</span> <span class="kt">char</span> <span class="o">*</span><span class="n">buf2</span> <span class="o">=</span> <span class="p">(</span><span class="kt">char</span> <span class="o">*</span><span class="p">)</span> <span class="n">malloc</span><span class="p">(</span><span class="n">BUFSIZ</span><span class="p">);</span> <span class="kt">char</span> <span class="o">*</span><span class="n">buf3</span> <span class="o">=</span> <span class="p">(</span><span class="kt">char</span> <span class="o">*</span><span class="p">)</span> <span class="n">PyMem_Malloc</span><span class="p">(</span><span class="n">BUFSIZ</span><span class="p">);</span> <span class="p">...</span> <span class="n">PyMem_Del</span><span class="p">(</span><span class="n">buf3</span><span class="p">);</span> <span class="cm">/* Wrong -- should be PyMem_Free() */</span> <span class="n">free</span><span class="p">(</span><span class="n">buf2</span><span class="p">);</span> <span class="cm">/* Right -- allocated via malloc() */</span> <span class="n">free</span><span class="p">(</span><span class="n">buf1</span><span class="p">);</span> <span class="cm">/* Fatal -- should be PyMem_Del() */</span> </pre></div> </div> <p>In addition to the functions aimed at handling raw memory blocks from the Python heap, objects in Python are allocated and released with <a class="reference internal" href="allocation.html#c.PyObject_New" title="PyObject_New"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_New()</span></code></a>, <a class="reference internal" href="allocation.html#c.PyObject_NewVar" title="PyObject_NewVar"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_NewVar()</span></code></a> and <a class="reference internal" href="allocation.html#c.PyObject_Del" title="PyObject_Del"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Del()</span></code></a>.</p> <p>These will be explained in the next chapter on defining and implementing new object types in C.</p> </div> </div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> <div class="sphinxsidebarwrapper"> <h3><a href="../contents.html">Table of Contents</a></h3> <ul> <li><a class="reference internal" href="#">Memory Management</a><ul> <li><a class="reference internal" href="#overview">Overview</a></li> <li><a class="reference internal" href="#raw-memory-interface">Raw Memory Interface</a></li> <li><a class="reference internal" href="#memory-interface">Memory Interface</a></li> <li><a class="reference internal" href="#object-allocators">Object allocators</a></li> <li><a class="reference internal" href="#default-memory-allocators">Default Memory Allocators</a></li> <li><a class="reference internal" href="#customize-memory-allocators">Customize Memory Allocators</a></li> <li><a class="reference internal" href="#the-pymalloc-allocator">The pymalloc allocator</a><ul> <li><a class="reference internal" href="#customize-pymalloc-arena-allocator">Customize pymalloc Arena Allocator</a></li> </ul> </li> <li><a class="reference internal" href="#tracemalloc-c-api">tracemalloc C API</a></li> <li><a class="reference internal" href="#examples">Examples</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="init.html" title="previous chapter">Initialization, Finalization, and Threads</a></p> <h4>Next topic</h4> <p class="topless"><a href="objimpl.html" title="next chapter">Object Implementation Support</a></p> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../bugs.html">Report a Bug</a></li> <li> <a href="https://github.com/python/cpython/blob/3.7/Doc/c-api/memory.rst" rel="nofollow">Show Source </a> </li> </ul> </div> </div> </div> <div class="clearer"></div> </div> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="objimpl.html" title="Object Implementation Support" >next</a> |</li> <li class="right" > <a href="init.html" title="Initialization, Finalization, and Threads" >previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li> <a href="../index.html">3.7.10 Documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" >Python/C API Reference Manual</a> »</li> <li class="right"> <div class="inline-search" style="display: none" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" type="text" name="q" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </div> <script type="text/javascript">$('.inline-search').show(0);</script> | </li> </ul> </div> <div class="footer"> © <a href="../copyright.html">Copyright</a> 2001-2021, Python Software Foundation. <br /> The Python Software Foundation is a non-profit corporation. <a href="https://www.python.org/psf/donations/">Please donate.</a> <br /> Last updated on Feb 26, 2021. <a href="../bugs.html">Found a bug</a>? <br /> Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 2.3.1. </div> </body> </html>