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<H1><A NAME="SECTION009500000000000000000">
7.5 <tt class="module">threading</tt> --
         Higher-level threading interface</A>
</H1>

<P>
<A NAME="module-threading"></A>

<P>
This module constructs higher-level threading interfaces on top of the 
lower level <tt class="module"><a href="module-thread.html">thread</a></tt> module.

<P>
The <tt class="module"><a href="module-dummythreading.html">dummy_threading</a></tt> module is provided for
situations where <tt class="module">threading</tt> cannot be used because
<tt class="module"><a href="module-thread.html">thread</a></tt> is missing.

<P>
This module defines the following functions and objects:

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-2704' xml:id='l2h-2704' class="function">activeCount</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Return the number of currently active <tt class="class">Thread</tt> objects.
The returned count is equal to the length of the list returned by
<tt class="function">enumerate()</tt>.
A function that returns the number of currently active threads.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-2705' xml:id='l2h-2705' class="function">Condition</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
A factory function that returns a new condition variable object.
A condition variable allows one or more threads to wait until they
are notified by another thread.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-2706' xml:id='l2h-2706' class="function">currentThread</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Return the current <tt class="class">Thread</tt> object, corresponding to the
caller's thread of control.  If the caller's thread of control was not
created through the
<tt class="module">threading</tt> module, a dummy thread object with limited functionality
is returned.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-2707' xml:id='l2h-2707' class="function">enumerate</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Return a list of all currently active <tt class="class">Thread</tt> objects.
The list includes daemonic threads, dummy thread objects created
by <tt class="function">currentThread()</tt>, and the main thread.  It excludes terminated
threads and threads that have not yet been started.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-2708' xml:id='l2h-2708' class="function">Event</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
A factory function that returns a new event object.  An event manages
a flag that can be set to true with the <tt class="method">set()</tt> method and
reset to false with the <tt class="method">clear()</tt> method.  The <tt class="method">wait()</tt>
method blocks until the flag is true.
</dl>

<P>
<dl><dt><b><span class="typelabel">class</span>&nbsp;<tt id='l2h-2709' xml:id='l2h-2709' class="class">local</tt></b>
<dd>
A class that represents thread-local data.  Thread-local data are data
whose values are thread specific.  To manage thread-local data, just
create an instance of <tt class="class">local</tt> (or a subclass) and store
attributes on it:

<P>
<div class="verbatim"><pre>
mydata = threading.local()
mydata.x = 1
</pre></div>

<P>
The instance's values will be different for separate threads.

<P>
For more details and extensive examples, see the documentation string
of the <tt class="module">_threading_local</tt> module.

<P>

<span class="versionnote">New in version 2.4.</span>

</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-2710' xml:id='l2h-2710' class="function">Lock</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
A factory function that returns a new primitive lock object.  Once
a thread has acquired it, subsequent attempts to acquire it block,
until it is released; any thread may release it.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-2711' xml:id='l2h-2711' class="function">RLock</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
A factory function that returns a new reentrant lock object.
A reentrant lock must be released by the thread that acquired it.
Once a thread has acquired a reentrant lock, the same thread may
acquire it again without blocking; the thread must release it once
for each time it has acquired it.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-2712' xml:id='l2h-2712' class="function">Semaphore</tt></b>(</nobr></td>
  <td><var></var><big>[</big><var>value</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
A factory function that returns a new semaphore object.  A
semaphore manages a counter representing the number of <tt class="method">release()</tt>
calls minus the number of <tt class="method">acquire()</tt> calls, plus an initial value.
The <tt class="method">acquire()</tt> method blocks if necessary until it can return
without making the counter negative.  If not given, <var>value</var> defaults to
1. 
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-2713' xml:id='l2h-2713' class="function">BoundedSemaphore</tt></b>(</nobr></td>
  <td><var></var><big>[</big><var>value</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
A factory function that returns a new bounded semaphore object.  A bounded
semaphore checks to make sure its current value doesn't exceed its initial
value.  If it does, <tt class="exception">ValueError</tt> is raised. In most situations
semaphores are used to guard resources with limited capacity.  If the
semaphore is released too many times it's a sign of a bug.  If not given,
<var>value</var> defaults to 1. 
</dl>

<P>
<dl><dt><b><span class="typelabel">class</span>&nbsp;<tt id='l2h-2714' xml:id='l2h-2714' class="class">Thread</tt></b>
<dd>
A class that represents a thread of control.  This class can be safely
subclassed in a limited fashion.
</dl>

<P>
<dl><dt><b><span class="typelabel">class</span>&nbsp;<tt id='l2h-2715' xml:id='l2h-2715' class="class">Timer</tt></b>
<dd>
A thread that executes a function after a specified interval has passed.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-2716' xml:id='l2h-2716' class="function">settrace</tt></b>(</nobr></td>
  <td><var>func</var>)</td></tr></table></dt>
<dd>
Set a trace function<a id='l2h-2718' xml:id='l2h-2718'></a> for all threads started
from the <tt class="module">threading</tt> module.  The <var>func</var> will be passed to 
<tt class="function">sys.settrace()</tt> for each thread, before its <tt class="method">run()</tt>
method is called.

<span class="versionnote">New in version 2.3.</span>

</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-2717' xml:id='l2h-2717' class="function">setprofile</tt></b>(</nobr></td>
  <td><var>func</var>)</td></tr></table></dt>
<dd>
Set a profile function<a id='l2h-2719' xml:id='l2h-2719'></a> for all threads started
from the <tt class="module">threading</tt> module.  The <var>func</var> will be passed to 
<tt class="function">sys.setprofile()</tt> for each thread, before its <tt class="method">run()</tt>
method is called.

<span class="versionnote">New in version 2.3.</span>

</dl>

<P>
Detailed interfaces for the objects are documented below.  

<P>
The design of this module is loosely based on Java's threading model.
However, where Java makes locks and condition variables basic behavior
of every object, they are separate objects in Python.  Python's <tt class="class">Thread</tt>
class supports a subset of the behavior of Java's Thread class;
currently, there are no priorities, no thread groups, and threads
cannot be destroyed, stopped, suspended, resumed, or interrupted.  The
static methods of Java's Thread class, when implemented, are mapped to
module-level functions.

<P>
All of the methods described below are executed atomically.

<P>

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<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>

<UL CLASS="ChildLinks">
<LI><A href="lock-objects.html">7.5.1 Lock Objects</a>
<LI><A href="rlock-objects.html">7.5.2 RLock Objects</a>
<LI><A href="condition-objects.html">7.5.3 Condition Objects</a>
<LI><A href="semaphore-objects.html">7.5.4 Semaphore Objects</a>
<UL>
<LI><A href="semaphore-examples.html">7.5.4.1 <tt class="class">Semaphore</tt> Example</a>
</ul>
<LI><A href="event-objects.html">7.5.5 Event Objects</a>
<LI><A href="thread-objects.html">7.5.6 Thread Objects</a>
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	54
	55	<H1><A NAME="SECTION009500000000000000000">
	56	7.5 <tt class="module">threading</tt> --
	57	Higher-level threading interface</A>
	58	</H1>
	59
	60	<P>
	61	<A NAME="module-threading"></A>
	62
	63	<P>
	64	This module constructs higher-level threading interfaces on top of the
65	lower level <tt class="module"><a href="module-thread.html">thread</a></tt> module.
66
67	<P>
68	The <tt class="module"><a href="module-dummythreading.html">dummy_threading</a></tt> module is provided for
69	situations where <tt class="module">threading</tt> cannot be used because
70	<tt class="module"><a href="module-thread.html">thread</a></tt> is missing.
71
72	<P>
73	This module defines the following functions and objects:
74
75	<P>
76	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
77	<td><nobr><b><tt id='l2h-2704' xml:id='l2h-2704' class="function">activeCount</tt></b>(</nobr></td>
78	<td><var></var>)</td></tr></table></dt>
79	<dd>
80	Return the number of currently active <tt class="class">Thread</tt> objects.
81	The returned count is equal to the length of the list returned by
82	<tt class="function">enumerate()</tt>.
83	A function that returns the number of currently active threads.
84	</dl>
85
86	<P>
87	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
88	<td><nobr><b><tt id='l2h-2705' xml:id='l2h-2705' class="function">Condition</tt></b>(</nobr></td>
89	<td><var></var>)</td></tr></table></dt>
90	<dd>
91	A factory function that returns a new condition variable object.
92	A condition variable allows one or more threads to wait until they
93	are notified by another thread.
94	</dl>
95
96	<P>
97	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
98	<td><nobr><b><tt id='l2h-2706' xml:id='l2h-2706' class="function">currentThread</tt></b>(</nobr></td>
99	<td><var></var>)</td></tr></table></dt>
100	<dd>
101	Return the current <tt class="class">Thread</tt> object, corresponding to the
102	caller's thread of control. If the caller's thread of control was not
103	created through the
104	<tt class="module">threading</tt> module, a dummy thread object with limited functionality
105	is returned.
106	</dl>
107
108	<P>
109	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
110	<td><nobr><b><tt id='l2h-2707' xml:id='l2h-2707' class="function">enumerate</tt></b>(</nobr></td>
111	<td><var></var>)</td></tr></table></dt>
112	<dd>
113	Return a list of all currently active <tt class="class">Thread</tt> objects.
114	The list includes daemonic threads, dummy thread objects created
115	by <tt class="function">currentThread()</tt>, and the main thread. It excludes terminated
116	threads and threads that have not yet been started.
117	</dl>
118
119	<P>
120	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
121	<td><nobr><b><tt id='l2h-2708' xml:id='l2h-2708' class="function">Event</tt></b>(</nobr></td>
122	<td><var></var>)</td></tr></table></dt>
123	<dd>
124	A factory function that returns a new event object. An event manages
125	a flag that can be set to true with the <tt class="method">set()</tt> method and
126	reset to false with the <tt class="method">clear()</tt> method. The <tt class="method">wait()</tt>
127	method blocks until the flag is true.
128	</dl>
129
130	<P>
131	<dl><dt><b><span class="typelabel">class</span> <tt id='l2h-2709' xml:id='l2h-2709' class="class">local</tt></b>
132	<dd>
133	A class that represents thread-local data. Thread-local data are data
134	whose values are thread specific. To manage thread-local data, just
135	create an instance of <tt class="class">local</tt> (or a subclass) and store
136	attributes on it:
137
138	<P>
139	<div class="verbatim"><pre>
140	mydata = threading.local()
141	mydata.x = 1
142	</pre></div>
143
144	<P>
145	The instance's values will be different for separate threads.
146
147	<P>
148	For more details and extensive examples, see the documentation string
149	of the <tt class="module">_threading_local</tt> module.
150
151	<P>
152
153	<span class="versionnote">New in version 2.4.</span>
154
155	</dl>
156
157	<P>
158	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
159	<td><nobr><b><tt id='l2h-2710' xml:id='l2h-2710' class="function">Lock</tt></b>(</nobr></td>
160	<td><var></var>)</td></tr></table></dt>
161	<dd>
162	A factory function that returns a new primitive lock object. Once
163	a thread has acquired it, subsequent attempts to acquire it block,
164	until it is released; any thread may release it.
165	</dl>
166
167	<P>
168	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
169	<td><nobr><b><tt id='l2h-2711' xml:id='l2h-2711' class="function">RLock</tt></b>(</nobr></td>
170	<td><var></var>)</td></tr></table></dt>
171	<dd>
172	A factory function that returns a new reentrant lock object.
173	A reentrant lock must be released by the thread that acquired it.
174	Once a thread has acquired a reentrant lock, the same thread may
175	acquire it again without blocking; the thread must release it once
176	for each time it has acquired it.
177	</dl>
178
179	<P>
180	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
181	<td><nobr><b><tt id='l2h-2712' xml:id='l2h-2712' class="function">Semaphore</tt></b>(</nobr></td>
182	<td><var></var><big>[</big><var>value</var><big>]</big><var></var>)</td></tr></table></dt>
183	<dd>
184	A factory function that returns a new semaphore object. A
185	semaphore manages a counter representing the number of <tt class="method">release()</tt>
186	calls minus the number of <tt class="method">acquire()</tt> calls, plus an initial value.
187	The <tt class="method">acquire()</tt> method blocks if necessary until it can return
188	without making the counter negative. If not given, <var>value</var> defaults to
189	1.
190	</dl>
191
192	<P>
193	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
194	<td><nobr><b><tt id='l2h-2713' xml:id='l2h-2713' class="function">BoundedSemaphore</tt></b>(</nobr></td>
195	<td><var></var><big>[</big><var>value</var><big>]</big><var></var>)</td></tr></table></dt>
196	<dd>
197	A factory function that returns a new bounded semaphore object. A bounded
198	semaphore checks to make sure its current value doesn't exceed its initial
199	value. If it does, <tt class="exception">ValueError</tt> is raised. In most situations
200	semaphores are used to guard resources with limited capacity. If the
201	semaphore is released too many times it's a sign of a bug. If not given,
202	<var>value</var> defaults to 1.
203	</dl>
204
205	<P>
206	<dl><dt><b><span class="typelabel">class</span> <tt id='l2h-2714' xml:id='l2h-2714' class="class">Thread</tt></b>
207	<dd>
208	A class that represents a thread of control. This class can be safely
209	subclassed in a limited fashion.
210	</dl>
211
212	<P>
213	<dl><dt><b><span class="typelabel">class</span> <tt id='l2h-2715' xml:id='l2h-2715' class="class">Timer</tt></b>
214	<dd>
215	A thread that executes a function after a specified interval has passed.
216	</dl>
217
218	<P>
219	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
220	<td><nobr><b><tt id='l2h-2716' xml:id='l2h-2716' class="function">settrace</tt></b>(</nobr></td>
221	<td><var>func</var>)</td></tr></table></dt>
222	<dd>
223	Set a trace function<a id='l2h-2718' xml:id='l2h-2718'></a> for all threads started
224	from the <tt class="module">threading</tt> module. The <var>func</var> will be passed to
225	<tt class="function">sys.settrace()</tt> for each thread, before its <tt class="method">run()</tt>
226	method is called.
227
228	<span class="versionnote">New in version 2.3.</span>
229
230	</dl>
231
232	<P>
233	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
234	<td><nobr><b><tt id='l2h-2717' xml:id='l2h-2717' class="function">setprofile</tt></b>(</nobr></td>
235	<td><var>func</var>)</td></tr></table></dt>
236	<dd>
237	Set a profile function<a id='l2h-2719' xml:id='l2h-2719'></a> for all threads started
238	from the <tt class="module">threading</tt> module. The <var>func</var> will be passed to
239	<tt class="function">sys.setprofile()</tt> for each thread, before its <tt class="method">run()</tt>
240	method is called.
241
242	<span class="versionnote">New in version 2.3.</span>
243
244	</dl>
245
246	<P>
247	Detailed interfaces for the objects are documented below.
248
249	<P>
250	The design of this module is loosely based on Java's threading model.
251	However, where Java makes locks and condition variables basic behavior
252	of every object, they are separate objects in Python. Python's <tt class="class">Thread</tt>
253	class supports a subset of the behavior of Java's Thread class;
254	currently, there are no priorities, no thread groups, and threads
255	cannot be destroyed, stopped, suspended, resumed, or interrupted. The
256	static methods of Java's Thread class, when implemented, are mapped to
257	module-level functions.
258
259	<P>
260	All of the methods described below are executed atomically.
261
262	<P>
263
264	<p><br /></p><hr class='online-navigation' />
265	<div class='online-navigation'>
266	<!--Table of Child-Links-->
267	<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
268
269	<UL CLASS="ChildLinks">
270	<LI><A href="lock-objects.html">7.5.1 Lock Objects</a>
271	<LI><A href="rlock-objects.html">7.5.2 RLock Objects</a>
272	<LI><A href="condition-objects.html">7.5.3 Condition Objects</a>
273	<LI><A href="semaphore-objects.html">7.5.4 Semaphore Objects</a>
274	<UL>
275	<LI><A href="semaphore-examples.html">7.5.4.1 <tt class="class">Semaphore</tt> Example</a>
276	</ul>
277	<LI><A href="event-objects.html">7.5.5 Event Objects</a>
278	<LI><A href="thread-objects.html">7.5.6 Thread Objects</a>
279	<LI><A href="timer-objects.html">7.5.7 Timer Objects</a>
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