projects / OpenSPARC-T2-DV / blame
| Commit | Line | Data |
|---|---|---|
| 86530b38 AT |
1 | <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> |
| 2 | <html> | |
| 3 | <head> | |
| 4 | <link rel="STYLESHEET" href="api.css" type='text/css' /> | |
| 5 | <link rel="SHORTCUT ICON" href="../icons/pyfav.png" type="image/png" /> | |
| 6 | <link rel='start' href='../index.html' title='Python Documentation Index' /> | |
| 7 | <link rel="first" href="api.html" title='Python/C API Reference Manual' /> | |
| 8 | <link rel='contents' href='contents.html' title="Contents" /> | |
| 9 | <link rel='index' href='genindex.html' title='Index' /> | |
| 10 | <link rel='last' href='about.html' title='About this document...' /> | |
| 11 | <link rel='help' href='about.html' title='About this document...' /> | |
| 12 | <link rel="next" href="memoryInterface.html" /> | |
| 13 | <link rel="prev" href="memory.html" /> | |
| 14 | <link rel="parent" href="memory.html" /> | |
| 15 | <link rel="next" href="memoryInterface.html" /> | |
| 16 | <meta name='aesop' content='information' /> | |
| 17 | <title>9.1 Overview </title> | |
| 18 | </head> | |
| 19 | <body> | |
| 20 | <DIV CLASS="navigation"> | |
| 21 | <div id='top-navigation-panel' xml:id='top-navigation-panel'> | |
| 22 | <table align="center" width="100%" cellpadding="0" cellspacing="2"> | |
| 23 | <tr> | |
| 24 | <td class='online-navigation'><a rel="prev" title="9. Memory Management" | |
| 25 | href="memory.html"><img src='../icons/previous.png' | |
| 26 | border='0' height='32' alt='Previous Page' width='32' /></A></td> | |
| 27 | <td class='online-navigation'><a rel="parent" title="9. Memory Management" | |
| 28 | href="memory.html"><img src='../icons/up.png' | |
| 29 | border='0' height='32' alt='Up One Level' width='32' /></A></td> | |
| 30 | <td class='online-navigation'><a rel="next" title="9.2 Memory Interface" | |
| 31 | href="memoryInterface.html"><img src='../icons/next.png' | |
| 32 | border='0' height='32' alt='Next Page' width='32' /></A></td> | |
| 33 | <td align="center" width="100%">Python/C API Reference Manual</td> | |
| 34 | <td class='online-navigation'><a rel="contents" title="Table of Contents" | |
| 35 | href="contents.html"><img src='../icons/contents.png' | |
| 36 | border='0' height='32' alt='Contents' width='32' /></A></td> | |
| 37 | <td class='online-navigation'><img src='../icons/blank.png' | |
| 38 | border='0' height='32' alt='' width='32' /></td> | |
| 39 | <td class='online-navigation'><a rel="index" title="Index" | |
| 40 | href="genindex.html"><img src='../icons/index.png' | |
| 41 | border='0' height='32' alt='Index' width='32' /></A></td> | |
| 42 | </tr></table> | |
| 43 | <div class='online-navigation'> | |
| 44 | <b class="navlabel">Previous:</b> | |
| 45 | <a class="sectref" rel="prev" href="memory.html">9. Memory Management</A> | |
| 46 | <b class="navlabel">Up:</b> | |
| 47 | <a class="sectref" rel="parent" href="memory.html">9. Memory Management</A> | |
| 48 | <b class="navlabel">Next:</b> | |
| 49 | <a class="sectref" rel="next" href="memoryInterface.html">9.2 Memory Interface</A> | |
| 50 | </div> | |
| 51 | <hr /></div> | |
| 52 | </DIV> | |
| 53 | <!--End of Navigation Panel--> | |
| 54 | ||
| 55 | <H1><A NAME="SECTION0011100000000000000000"></A><A NAME="memoryOverview"></A> | |
| 56 | <BR> | |
| 57 | 9.1 Overview | |
| 58 | </H1> | |
| 59 | ||
| 60 | <P> | |
| 61 | Memory management in Python involves a private heap containing all | |
| 62 | Python objects and data structures. The management of this private | |
| 63 | heap is ensured internally by the <em>Python memory manager</em>. The | |
| 64 | Python memory manager has different components which deal with various | |
| 65 | dynamic storage management aspects, like sharing, segmentation, | |
| 66 | preallocation or caching. | |
| 67 | ||
| 68 | <P> | |
| 69 | At the lowest level, a raw memory allocator ensures that there is | |
| 70 | enough room in the private heap for storing all Python-related data | |
| 71 | by interacting with the memory manager of the operating system. On top | |
| 72 | of the raw memory allocator, several object-specific allocators | |
| 73 | operate on the same heap and implement distinct memory management | |
| 74 | policies adapted to the peculiarities of every object type. For | |
| 75 | example, integer objects are managed differently within the heap than | |
| 76 | strings, tuples or dictionaries because integers imply different | |
| 77 | storage requirements and speed/space tradeoffs. The Python memory | |
| 78 | manager thus delegates some of the work to the object-specific | |
| 79 | allocators, but ensures that the latter operate within the bounds of | |
| 80 | the private heap. | |
| 81 | ||
| 82 | <P> | |
| 83 | It is important to understand that the management of the Python heap | |
| 84 | is performed by the interpreter itself and that the user has no | |
| 85 | control over it, even if she regularly manipulates object pointers to | |
| 86 | memory blocks inside that heap. The allocation of heap space for | |
| 87 | Python objects and other internal buffers is performed on demand by | |
| 88 | the Python memory manager through the Python/C API functions listed in | |
| 89 | this document. | |
| 90 | ||
| 91 | <P> | |
| 92 | To avoid memory corruption, extension writers should never try to | |
| 93 | operate on Python objects with the functions exported by the C | |
| 94 | library: <tt class="cfunction">malloc()</tt><a id='l2h-895' xml:id='l2h-895'></a>, | |
| 95 | <tt class="cfunction">calloc()</tt><a id='l2h-896' xml:id='l2h-896'></a>, | |
| 96 | <tt class="cfunction">realloc()</tt><a id='l2h-897' xml:id='l2h-897'></a> and | |
| 97 | <tt class="cfunction">free()</tt><a id='l2h-898' xml:id='l2h-898'></a>. This will result in | |
| 98 | mixed calls between the C allocator and the Python memory manager | |
| 99 | with fatal consequences, because they implement different algorithms | |
| 100 | and operate on different heaps. However, one may safely allocate and | |
| 101 | release memory blocks with the C library allocator for individual | |
| 102 | purposes, as shown in the following example: | |
| 103 | ||
| 104 | <P> | |
| 105 | <div class="verbatim"><pre> | |
| 106 | PyObject *res; | |
| 107 | char *buf = (char *) malloc(BUFSIZ); /* for I/O */ | |
| 108 | ||
| 109 | if (buf == NULL) | |
| 110 | return PyErr_NoMemory(); | |
| 111 | ...Do some I/O operation involving buf... | |
| 112 | res = PyString_FromString(buf); | |
| 113 | free(buf); /* malloc'ed */ | |
| 114 | return res; | |
| 115 | </pre></div> | |
| 116 | ||
| 117 | <P> | |
| 118 | In this example, the memory request for the I/O buffer is handled by | |
| 119 | the C library allocator. The Python memory manager is involved only | |
| 120 | in the allocation of the string object returned as a result. | |
| 121 | ||
| 122 | <P> | |
| 123 | In most situations, however, it is recommended to allocate memory from | |
| 124 | the Python heap specifically because the latter is under control of | |
| 125 | the Python memory manager. For example, this is required when the | |
| 126 | interpreter is extended with new object types written in C. Another | |
| 127 | reason for using the Python heap is the desire to <em>inform</em> the | |
| 128 | Python memory manager about the memory needs of the extension module. | |
| 129 | Even when the requested memory is used exclusively for internal, | |
| 130 | highly-specific purposes, delegating all memory requests to the Python | |
| 131 | memory manager causes the interpreter to have a more accurate image of | |
| 132 | its memory footprint as a whole. Consequently, under certain | |
| 133 | circumstances, the Python memory manager may or may not trigger | |
| 134 | appropriate actions, like garbage collection, memory compaction or | |
| 135 | other preventive procedures. Note that by using the C library | |
| 136 | allocator as shown in the previous example, the allocated memory for | |
| 137 | the I/O buffer escapes completely the Python memory manager. | |
| 138 | ||
| 139 | <P> | |
| 140 | ||
| 141 | <DIV CLASS="navigation"> | |
| 142 | <div class='online-navigation'> | |
| 143 | <p></p><hr /> | |
| 144 | <table align="center" width="100%" cellpadding="0" cellspacing="2"> | |
| 145 | <tr> | |
| 146 | <td class='online-navigation'><a rel="prev" title="9. Memory Management" | |
| 147 | href="memory.html"><img src='../icons/previous.png' | |
| 148 | border='0' height='32' alt='Previous Page' width='32' /></A></td> | |
| 149 | <td class='online-navigation'><a rel="parent" title="9. Memory Management" | |
| 150 | href="memory.html"><img src='../icons/up.png' | |
| 151 | border='0' height='32' alt='Up One Level' width='32' /></A></td> | |
| 152 | <td class='online-navigation'><a rel="next" title="9.2 Memory Interface" | |
| 153 | href="memoryInterface.html"><img src='../icons/next.png' | |
| 154 | border='0' height='32' alt='Next Page' width='32' /></A></td> | |
| 155 | <td align="center" width="100%">Python/C API Reference Manual</td> | |
| 156 | <td class='online-navigation'><a rel="contents" title="Table of Contents" | |
| 157 | href="contents.html"><img src='../icons/contents.png' | |
| 158 | border='0' height='32' alt='Contents' width='32' /></A></td> | |
| 159 | <td class='online-navigation'><img src='../icons/blank.png' | |
| 160 | border='0' height='32' alt='' width='32' /></td> | |
| 161 | <td class='online-navigation'><a rel="index" title="Index" | |
| 162 | href="genindex.html"><img src='../icons/index.png' | |
| 163 | border='0' height='32' alt='Index' width='32' /></A></td> | |
| 164 | </tr></table> | |
| 165 | <div class='online-navigation'> | |
| 166 | <b class="navlabel">Previous:</b> | |
| 167 | <a class="sectref" rel="prev" href="memory.html">9. Memory Management</A> | |
| 168 | <b class="navlabel">Up:</b> | |
| 169 | <a class="sectref" rel="parent" href="memory.html">9. Memory Management</A> | |
| 170 | <b class="navlabel">Next:</b> | |
| 171 | <a class="sectref" rel="next" href="memoryInterface.html">9.2 Memory Interface</A> | |
| 172 | </div> | |
| 173 | </div> | |
| 174 | <hr /> | |
| 175 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
| 176 | </DIV> | |
| 177 | <!--End of Navigation Panel--> | |
| 178 | <ADDRESS> | |
| 179 | See <i><a href="about.html">About this document...</a></i> for information on suggesting changes. | |
| 180 | </ADDRESS> | |
| 181 | </BODY> | |
| 182 | </HTML> |