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Issue #16199: Backport 2to3 typo fix from 3.2.
author Chris Jerdonek <chris.jerdonek@gmail.com>
date Thu, 11 Oct 2012 16:15:46 -0700
parents 8aab13719c02
children
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1 :mod:`thread` --- Multiple threads of control
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2 =============================================
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3
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4 .. module:: thread
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5 :synopsis: Create multiple threads of control within one interpreter.
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6
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7 .. note::
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8 The :mod:`thread` module has been renamed to :mod:`_thread` in Python 3.
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9 The :term:`2to3` tool will automatically adapt imports when converting your
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10 sources to Python 3; however, you should consider using the high-level
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11 :mod:`threading` module instead.
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12
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13
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14 .. index::
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15 single: light-weight processes
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16 single: processes, light-weight
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17 single: binary semaphores
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18 single: semaphores, binary
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19
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20 This module provides low-level primitives for working with multiple threads
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21 (also called :dfn:`light-weight processes` or :dfn:`tasks`) --- multiple threads of
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22 control sharing their global data space. For synchronization, simple locks
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23 (also called :dfn:`mutexes` or :dfn:`binary semaphores`) are provided.
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24 The :mod:`threading` module provides an easier to use and higher-level
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25 threading API built on top of this module.
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26
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27 .. index::
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28 single: pthreads
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29 pair: threads; POSIX
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30
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31 The module is optional. It is supported on Windows, Linux, SGI IRIX, Solaris
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32 2.x, as well as on systems that have a POSIX thread (a.k.a. "pthread")
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33 implementation. For systems lacking the :mod:`thread` module, the
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34 :mod:`dummy_thread` module is available. It duplicates this module's interface
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35 and can be used as a drop-in replacement.
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36
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37 It defines the following constant and functions:
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38
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39
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40 .. exception:: error
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41
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42 Raised on thread-specific errors.
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43
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44
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45 .. data:: LockType
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46
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47 This is the type of lock objects.
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48
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49
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50 .. function:: start_new_thread(function, args[, kwargs])
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51
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52 Start a new thread and return its identifier. The thread executes the function
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53 *function* with the argument list *args* (which must be a tuple). The optional
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54 *kwargs* argument specifies a dictionary of keyword arguments. When the function
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55 returns, the thread silently exits. When the function terminates with an
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56 unhandled exception, a stack trace is printed and then the thread exits (but
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57 other threads continue to run).
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58
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59
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60 .. function:: interrupt_main()
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61
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62 Raise a :exc:`KeyboardInterrupt` exception in the main thread. A subthread can
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63 use this function to interrupt the main thread.
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64
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65 .. versionadded:: 2.3
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66
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67
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68 .. function:: exit()
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69
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70 Raise the :exc:`SystemExit` exception. When not caught, this will cause the
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71 thread to exit silently.
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72
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73 ..
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74 function:: exit_prog(status)
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75
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76 Exit all threads and report the value of the integer argument
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77 *status* as the exit status of the entire program.
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78 **Caveat:** code in pending :keyword:`finally` clauses, in this thread
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79 or in other threads, is not executed.
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80
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81
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82 .. function:: allocate_lock()
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83
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84 Return a new lock object. Methods of locks are described below. The lock is
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85 initially unlocked.
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86
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87
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88 .. function:: get_ident()
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89
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90 Return the 'thread identifier' of the current thread. This is a nonzero
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91 integer. Its value has no direct meaning; it is intended as a magic cookie to
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92 be used e.g. to index a dictionary of thread-specific data. Thread identifiers
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93 may be recycled when a thread exits and another thread is created.
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94
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95
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96 .. function:: stack_size([size])
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97
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98 Return the thread stack size used when creating new threads. The optional
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99 *size* argument specifies the stack size to be used for subsequently created
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100 threads, and must be 0 (use platform or configured default) or a positive
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101 integer value of at least 32,768 (32kB). If changing the thread stack size is
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102 unsupported, the :exc:`error` exception is raised. If the specified stack size is
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103 invalid, a :exc:`ValueError` is raised and the stack size is unmodified. 32kB
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104 is currently the minimum supported stack size value to guarantee sufficient
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105 stack space for the interpreter itself. Note that some platforms may have
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106 particular restrictions on values for the stack size, such as requiring a
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107 minimum stack size > 32kB or requiring allocation in multiples of the system
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108 memory page size - platform documentation should be referred to for more
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109 information (4kB pages are common; using multiples of 4096 for the stack size is
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110 the suggested approach in the absence of more specific information).
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111 Availability: Windows, systems with POSIX threads.
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112
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113 .. versionadded:: 2.5
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114
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115
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116 Lock objects have the following methods:
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117
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118
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119 .. method:: lock.acquire([waitflag])
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120
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121 Without the optional argument, this method acquires the lock unconditionally, if
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122 necessary waiting until it is released by another thread (only one thread at a
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123 time can acquire a lock --- that's their reason for existence). If the integer
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124 *waitflag* argument is present, the action depends on its value: if it is zero,
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125 the lock is only acquired if it can be acquired immediately without waiting,
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126 while if it is nonzero, the lock is acquired unconditionally as before. The
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127 return value is ``True`` if the lock is acquired successfully, ``False`` if not.
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128
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129
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130 .. method:: lock.release()
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131
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132 Releases the lock. The lock must have been acquired earlier, but not
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133 necessarily by the same thread.
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134
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135
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136 .. method:: lock.locked()
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137
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138 Return the status of the lock: ``True`` if it has been acquired by some thread,
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139 ``False`` if not.
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140
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141 In addition to these methods, lock objects can also be used via the
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142 :keyword:`with` statement, e.g.::
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143
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144 import thread
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145
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146 a_lock = thread.allocate_lock()
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147
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148 with a_lock:
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149 print "a_lock is locked while this executes"
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150
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151 **Caveats:**
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152
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153 .. index:: module: signal
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154
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155 * Threads interact strangely with interrupts: the :exc:`KeyboardInterrupt`
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156 exception will be received by an arbitrary thread. (When the :mod:`signal`
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157 module is available, interrupts always go to the main thread.)
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158
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159 * Calling :func:`sys.exit` or raising the :exc:`SystemExit` exception is
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160 equivalent to calling :func:`thread.exit`.
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161
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162 * Not all built-in functions that may block waiting for I/O allow other threads
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163 to run. (The most popular ones (:func:`time.sleep`, :meth:`file.read`,
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164 :func:`select.select`) work as expected.)
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165
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166 * It is not possible to interrupt the :meth:`acquire` method on a lock --- the
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167 :exc:`KeyboardInterrupt` exception will happen after the lock has been acquired.
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168
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169 .. index:: pair: threads; IRIX
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170
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171 * When the main thread exits, it is system defined whether the other threads
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172 survive. On SGI IRIX using the native thread implementation, they survive. On
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173 most other systems, they are killed without executing :keyword:`try` ...
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174 :keyword:`finally` clauses or executing object destructors.
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175
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176 * When the main thread exits, it does not do any of its usual cleanup (except
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177 that :keyword:`try` ... :keyword:`finally` clauses are honored), and the
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178 standard I/O files are not flushed.
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179