projects / OpenSPARC-T2-SAM / blame
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| 54 | ||
| 55 | <H1><A NAME="SECTION005000000000000000000"></A><A NAME="countingRefs"></A> | |
| 56 | <BR> | |
| 57 | 3. Reference Counting | |
| 58 | </H1> | |
| 59 | ||
| 60 | <P> | |
| 61 | The macros in this section are used for managing reference counts | |
| 62 | of Python objects. | |
| 63 | ||
| 64 | <P> | |
| 65 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"><td><nobr>void <b><tt id='l2h-84' xml:id='l2h-84' class="cfunction">Py_INCREF</tt></b>(</nobr></td><td>PyObject *<var>o</var>)</td></tr></table></dt> | |
| 66 | <dd> | |
| 67 | Increment the reference count for object <var>o</var>. The object must | |
| 68 | not be <tt class="constant">NULL</tt>; if you aren't sure that it isn't <tt class="constant">NULL</tt>, use | |
| 69 | <tt class="cfunction">Py_XINCREF()</tt>. | |
| 70 | </dd></dl> | |
| 71 | ||
| 72 | <P> | |
| 73 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"><td><nobr>void <b><tt id='l2h-85' xml:id='l2h-85' class="cfunction">Py_XINCREF</tt></b>(</nobr></td><td>PyObject *<var>o</var>)</td></tr></table></dt> | |
| 74 | <dd> | |
| 75 | Increment the reference count for object <var>o</var>. The object may be | |
| 76 | <tt class="constant">NULL</tt>, in which case the macro has no effect. | |
| 77 | </dd></dl> | |
| 78 | ||
| 79 | <P> | |
| 80 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"><td><nobr>void <b><tt id='l2h-86' xml:id='l2h-86' class="cfunction">Py_DECREF</tt></b>(</nobr></td><td>PyObject *<var>o</var>)</td></tr></table></dt> | |
| 81 | <dd> | |
| 82 | Decrement the reference count for object <var>o</var>. The object must | |
| 83 | not be <tt class="constant">NULL</tt>; if you aren't sure that it isn't <tt class="constant">NULL</tt>, use | |
| 84 | <tt class="cfunction">Py_XDECREF()</tt>. If the reference count reaches zero, the | |
| 85 | object's type's deallocation function (which must not be <tt class="constant">NULL</tt>) is | |
| 86 | invoked. | |
| 87 | ||
| 88 | <P> | |
| 89 | <span class="warning"><b class="label">Warning:</b> | |
| 90 | The deallocation function can cause arbitrary Python code | |
| 91 | to be invoked (e.g. when a class instance with a <tt class="method">__del__()</tt> | |
| 92 | method is deallocated). While exceptions in such code are not | |
| 93 | propagated, the executed code has free access to all Python global | |
| 94 | variables. This means that any object that is reachable from a | |
| 95 | global variable should be in a consistent state before | |
| 96 | <tt class="cfunction">Py_DECREF()</tt> is invoked. For example, code to delete an | |
| 97 | object from a list should copy a reference to the deleted object in | |
| 98 | a temporary variable, update the list data structure, and then call | |
| 99 | <tt class="cfunction">Py_DECREF()</tt> for the temporary variable.</span> | |
| 100 | </dd></dl> | |
| 101 | ||
| 102 | <P> | |
| 103 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"><td><nobr>void <b><tt id='l2h-87' xml:id='l2h-87' class="cfunction">Py_XDECREF</tt></b>(</nobr></td><td>PyObject *<var>o</var>)</td></tr></table></dt> | |
| 104 | <dd> | |
| 105 | Decrement the reference count for object <var>o</var>. The object may be | |
| 106 | <tt class="constant">NULL</tt>, in which case the macro has no effect; otherwise the effect | |
| 107 | is the same as for <tt class="cfunction">Py_DECREF()</tt>, and the same warning | |
| 108 | applies. | |
| 109 | </dd></dl> | |
| 110 | ||
| 111 | <P> | |
| 112 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"><td><nobr>void <b><tt id='l2h-88' xml:id='l2h-88' class="cfunction">Py_CLEAR</tt></b>(</nobr></td><td>PyObject *<var>o</var>)</td></tr></table></dt> | |
| 113 | <dd> | |
| 114 | Decrement the reference count for object <var>o</var>. The object may be | |
| 115 | <tt class="constant">NULL</tt>, in which case the macro has no effect; otherwise the effect | |
| 116 | is the same as for <tt class="cfunction">Py_DECREF()</tt>, except that the argument | |
| 117 | is also set to <tt class="constant">NULL</tt>. The warning for <tt class="cfunction">Py_DECREF()</tt> does | |
| 118 | not apply with respect to the object passed because the macro | |
| 119 | carefully uses a temporary variable and sets the argument to <tt class="constant">NULL</tt> | |
| 120 | before decrementing its reference count. | |
| 121 | ||
| 122 | <P> | |
| 123 | It is a good idea to use this macro whenever decrementing the value | |
| 124 | of a variable that might be traversed during garbage collection. | |
| 125 | ||
| 126 | <P> | |
| 127 | ||
| 128 | <span class="versionnote">New in version 2.4.</span> | |
| 129 | ||
| 130 | </dd></dl> | |
| 131 | ||
| 132 | <P> | |
| 133 | The following functions are for runtime dynamic embedding of Python: | |
| 134 | <tt class="cfunction">Py_IncRef(PyObject *o)</tt>, <tt class="cfunction">Py_DecRef(PyObject *o)</tt>. | |
| 135 | They are simply exported function versions of <tt class="cfunction">Py_XINCREF()</tt> and | |
| 136 | <tt class="cfunction">Py_XDECREF()</tt>, respectively. | |
| 137 | ||
| 138 | <P> | |
| 139 | The following functions or macros are only for use within the | |
| 140 | interpreter core: <tt class="cfunction">_Py_Dealloc()</tt>, | |
| 141 | <tt class="cfunction">_Py_ForgetReference()</tt>, <tt class="cfunction">_Py_NewReference()</tt>, as | |
| 142 | well as the global variable <tt class="cdata">_Py_RefTotal</tt>. | |
| 143 | ||
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| 178 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
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