[OpenSPARC-T2-SAM] / sam-t2 / devtools / amd64 / html / python / lib / module-thread.html

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<link rel="STYLESHEET" href="lib.css" type='text/css' />
<link rel="SHORTCUT ICON" href="../icons/pyfav.png" type="image/png" />
<link rel='start' href='../index.html' title='Python Documentation Index' />
<link rel="first" href="lib.html" title='Python Library Reference' />
<link rel='contents' href='contents.html' title="Contents" />
<link rel='index' href='genindex.html' title='Index' />
<link rel='last' href='about.html' title='About this document...' />
<link rel='help' href='about.html' title='About this document...' />
<link rel="next" href="module-threading.html" />
<link rel="prev" href="module-select.html" />
<link rel="parent" href="someos.html" />
<link rel="next" href="module-threading.html" />
<meta name='aesop' content='information' />
<title>7.4 thread -- Multiple threads of control</title>
</head>
<body>
<DIV CLASS="navigation">
<div id='top-navigation-panel' xml:id='top-navigation-panel'>
<table align="center" width="100%" cellpadding="0" cellspacing="2">
<tr>
<td class='online-navigation'><a rel="prev" title="7.3.1 Polling Objects"
  href="poll-objects.html"><img src='../icons/previous.png'
  border='0' height='32'  alt='Previous Page' width='32' /></A></td>
<td class='online-navigation'><a rel="parent" title="7. Optional Operating System"
  href="someos.html"><img src='../icons/up.png'
  border='0' height='32'  alt='Up One Level' width='32' /></A></td>
<td class='online-navigation'><a rel="next" title="7.5 threading  "
  href="module-threading.html"><img src='../icons/next.png'
  border='0' height='32'  alt='Next Page' width='32' /></A></td>
<td align="center" width="100%">Python Library Reference</td>
<td class='online-navigation'><a rel="contents" title="Table of Contents"
  href="contents.html"><img src='../icons/contents.png'
  border='0' height='32'  alt='Contents' width='32' /></A></td>
<td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png'
  border='0' height='32'  alt='Module Index' width='32' /></a></td>
<td class='online-navigation'><a rel="index" title="Index"
  href="genindex.html"><img src='../icons/index.png'
  border='0' height='32'  alt='Index' width='32' /></A></td>
</tr></table>
<div class='online-navigation'>
<b class="navlabel">Previous:</b>
<a class="sectref" rel="prev" href="poll-objects.html">7.3.1 Polling Objects</A>
<b class="navlabel">Up:</b>
<a class="sectref" rel="parent" href="someos.html">7. Optional Operating System</A>
<b class="navlabel">Next:</b>
<a class="sectref" rel="next" href="module-threading.html">7.5 threading  </A>
</div>
<hr /></div>
</DIV>
<!--End of Navigation Panel-->

<H1><A NAME="SECTION009400000000000000000">
7.4 <tt class="module">thread</tt> --
         Multiple threads of control</A>
</H1>

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

<P>
This module provides low-level primitives for working with multiple
threads (a.k.a. <i class="dfn">light-weight processes</i> or <i class="dfn">tasks</i>) -- multiple
threads of control sharing their global data space.  For
synchronization, simple locks (a.k.a. <i class="dfn">mutexes</i> or <i class="dfn">binary
semaphores</i>) are provided.
<a id='l2h-2700' xml:id='l2h-2700'></a>

<P>
The module is optional.  It is supported on Windows, Linux, SGI
IRIX, Solaris 2.x, as well as on systems that have a POSIX thread
(a.k.a. ``pthread'') implementation.  For systems lacking the <tt class="module">thread</tt>
module, the <tt class="module"><a href="module-dummythread.html">dummy_thread</a></tt> module is available.
It duplicates this module's interface and can be
used as a drop-in replacement.
<a id='l2h-2701' xml:id='l2h-2701'></a>
<a id='l2h-2688' xml:id='l2h-2688'></a>
<P>
It defines the following constant and functions:

<P>
<dl><dt><b><span class="typelabel">exception</span>&nbsp;<tt id='l2h-2689' xml:id='l2h-2689' class="exception">error</tt></b></dt>
<dd>
Raised on thread-specific errors.
</dd></dl>

<P>
<dl><dt><b><tt id='l2h-2690' xml:id='l2h-2690'>LockType</tt></b></dt>
<dd>
This is the type of lock objects.
</dd></dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-2691' xml:id='l2h-2691' class="function">start_new_thread</tt></b>(</nobr></td>
  <td><var>function, args</var><big>[</big><var>, kwargs</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
Start a new thread and return its identifier.  The thread executes the function
<var>function</var> with the argument list <var>args</var> (which must be a tuple).  The
optional <var>kwargs</var> argument specifies a dictionary of keyword arguments.
When the function returns, the thread silently exits.  When the function
terminates with an unhandled exception, a stack trace is printed and
then the thread exits (but other threads continue to run).
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-2692' xml:id='l2h-2692' class="function">interrupt_main</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Raise a KeyboardInterrupt in the main thread.  A subthread can use this
function to interrupt the main thread.

<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-2693' xml:id='l2h-2693' class="function">exit</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Raise the <tt class="exception">SystemExit</tt> exception.  When not caught, this
will cause the thread to exit silently.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-2694' xml:id='l2h-2694' class="function">allocate_lock</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Return a new lock object.  Methods of locks are described below.  The
lock is initially unlocked.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-2695' xml:id='l2h-2695' class="function">get_ident</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Return the `thread identifier' of the current thread.  This is a
nonzero integer.  Its value has no direct meaning; it is intended as a
magic cookie to be used e.g. to index a dictionary of thread-specific
data.  Thread identifiers may be recycled when a thread exits and
another thread is created.
</dl>

<P>
Lock objects have the following methods:

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-2696' xml:id='l2h-2696' class="method">acquire</tt></b>(</nobr></td>
  <td><var></var><big>[</big><var>waitflag</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
Without the optional argument, this method acquires the lock
unconditionally, if necessary waiting until it is released by another
thread (only one thread at a time can acquire a lock -- that's their
reason for existence).  If the integer
<var>waitflag</var> argument is present, the action depends on its
value: if it is zero, the lock is only acquired if it can be acquired
immediately without waiting, while if it is nonzero, the lock is
acquired unconditionally as before.  The
return value is <code>True</code> if the lock is acquired successfully,
<code>False</code> if not.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-2697' xml:id='l2h-2697' class="method">release</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Releases the lock.  The lock must have been acquired earlier, but not
necessarily by the same thread.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-2698' xml:id='l2h-2698' class="method">locked</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Return the status of the lock: <code>True</code> if it has been acquired by
some thread, <code>False</code> if not.
</dl>

<P>
<strong>Caveats:</strong>

<P>

<UL>
<LI>Threads interact strangely with interrupts: the
<tt class="exception">KeyboardInterrupt</tt> exception will be received by an
arbitrary thread.  (When the <tt class="module"><a href="module-signal.html">signal</a></tt><a id='l2h-2702' xml:id='l2h-2702'></a>
module is available, interrupts always go to the main thread.)

<P>
</LI>
<LI>Calling <tt class="function">sys.exit()</tt> or raising the <tt class="exception">SystemExit</tt>
exception is equivalent to calling <tt class="function">exit()</tt>.

<P>
</LI>
<LI>Not all built-in functions that may block waiting for I/O allow other
threads to run.  (The most popular ones (<tt class="function">time.sleep()</tt>,
<tt class="method"><var>file</var>.read()</tt>, <tt class="function">select.select()</tt>) work as
expected.)

<P>
</LI>
<LI>It is not possible to interrupt the <tt class="method">acquire()</tt> method on a lock
-- the <tt class="exception">KeyboardInterrupt</tt> exception will happen after the
lock has been acquired.

<P>
</LI>
<LI>When the main thread exits, it is system defined whether the other
threads survive.  On SGI IRIX using the native thread implementation,
they survive.  On most other systems, they are killed without
executing <tt class="keyword">try</tt> ... <tt class="keyword">finally</tt> clauses or executing
object destructors.
<a id='l2h-2699' xml:id='l2h-2699'></a>
<P>
</LI>
<LI>When the main thread exits, it does not do any of its usual cleanup
(except that <tt class="keyword">try</tt> ... <tt class="keyword">finally</tt> clauses are honored),
and the standard I/O files are not flushed.

<P>
</LI>
</UL>

<DIV CLASS="navigation">
<div class='online-navigation'>
<p></p><hr />
<table align="center" width="100%" cellpadding="0" cellspacing="2">
<tr>
<td class='online-navigation'><a rel="prev" title="7.3.1 Polling Objects"
  href="poll-objects.html"><img src='../icons/previous.png'
  border='0' height='32'  alt='Previous Page' width='32' /></A></td>
<td class='online-navigation'><a rel="parent" title="7. Optional Operating System"
  href="someos.html"><img src='../icons/up.png'
  border='0' height='32'  alt='Up One Level' width='32' /></A></td>
<td class='online-navigation'><a rel="next" title="7.5 threading  "
  href="module-threading.html"><img src='../icons/next.png'
  border='0' height='32'  alt='Next Page' width='32' /></A></td>
<td align="center" width="100%">Python Library Reference</td>
<td class='online-navigation'><a rel="contents" title="Table of Contents"
  href="contents.html"><img src='../icons/contents.png'
  border='0' height='32'  alt='Contents' width='32' /></A></td>
<td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png'
  border='0' height='32'  alt='Module Index' width='32' /></a></td>
<td class='online-navigation'><a rel="index" title="Index"
  href="genindex.html"><img src='../icons/index.png'
  border='0' height='32'  alt='Index' width='32' /></A></td>
</tr></table>
<div class='online-navigation'>
<b class="navlabel">Previous:</b>
<a class="sectref" rel="prev" href="poll-objects.html">7.3.1 Polling Objects</A>
<b class="navlabel">Up:</b>
<a class="sectref" rel="parent" href="someos.html">7. Optional Operating System</A>
<b class="navlabel">Next:</b>
<a class="sectref" rel="next" href="module-threading.html">7.5 threading  </A>
</div>
</div>
<hr />
<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
</DIV>
<!--End of Navigation Panel-->
<ADDRESS>
See <i><a href="about.html">About this document...</a></i> for information on suggesting changes.
</ADDRESS>
</BODY>
</HTML>
Commit	Line	Data
920dae64 AT	1	<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
	2	<html>
	3	<head>
	4	<link rel="STYLESHEET" href="lib.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="lib.html" title='Python Library Reference' />
	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="module-threading.html" />
	13	<link rel="prev" href="module-select.html" />
	14	<link rel="parent" href="someos.html" />
	15	<link rel="next" href="module-threading.html" />
	16	<meta name='aesop' content='information' />
	17	<title>7.4 thread -- Multiple threads of control</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="7.3.1 Polling Objects"
	25	href="poll-objects.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="7. Optional Operating System"
	28	href="someos.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="7.5 threading "
	31	href="module-threading.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 Library Reference</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'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png'
	38	border='0' height='32' alt='Module Index' width='32' /></a></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="poll-objects.html">7.3.1 Polling Objects</A>
	46	<b class="navlabel">Up:</b>
	47	<a class="sectref" rel="parent" href="someos.html">7. Optional Operating System</A>
	48	<b class="navlabel">Next:</b>
	49	<a class="sectref" rel="next" href="module-threading.html">7.5 threading </A>
	50	</div>
	51	<hr /></div>
	52	</DIV>
	53	<!--End of Navigation Panel-->
	54
	55	<H1><A NAME="SECTION009400000000000000000">
	56	7.4 <tt class="module">thread</tt> --
	57	Multiple threads of control</A>
	58	</H1>
	59
	60	<P>
	61	<A NAME="module-thread"></A>
	62
	63	<P>
	64	This module provides low-level primitives for working with multiple
65	threads (a.k.a. <i class="dfn">light-weight processes</i> or <i class="dfn">tasks</i>) -- multiple
66	threads of control sharing their global data space. For
67	synchronization, simple locks (a.k.a. <i class="dfn">mutexes</i> or <i class="dfn">binary
68	semaphores</i>) are provided.
69	<a id='l2h-2700' xml:id='l2h-2700'></a>
70
71	<P>
72	The module is optional. It is supported on Windows, Linux, SGI
73	IRIX, Solaris 2.x, as well as on systems that have a POSIX thread
74	(a.k.a. ``pthread'') implementation. For systems lacking the <tt class="module">thread</tt>
75	module, the <tt class="module"><a href="module-dummythread.html">dummy_thread</a></tt> module is available.
76	It duplicates this module's interface and can be
77	used as a drop-in replacement.
78	<a id='l2h-2701' xml:id='l2h-2701'></a>
79	<a id='l2h-2688' xml:id='l2h-2688'></a>
80	<P>
81	It defines the following constant and functions:
82
83	<P>
84	<dl><dt><b><span class="typelabel">exception</span> <tt id='l2h-2689' xml:id='l2h-2689' class="exception">error</tt></b></dt>
85	<dd>
86	Raised on thread-specific errors.
87	</dd></dl>
88
89	<P>
90	<dl><dt><b><tt id='l2h-2690' xml:id='l2h-2690'>LockType</tt></b></dt>
91	<dd>
92	This is the type of lock objects.
93	</dd></dl>
94
95	<P>
96	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
97	<td><nobr><b><tt id='l2h-2691' xml:id='l2h-2691' class="function">start_new_thread</tt></b>(</nobr></td>
98	<td><var>function, args</var><big>[</big><var>, kwargs</var><big>]</big><var></var>)</td></tr></table></dt>
99	<dd>
100	Start a new thread and return its identifier. The thread executes the function
101	<var>function</var> with the argument list <var>args</var> (which must be a tuple). The
102	optional <var>kwargs</var> argument specifies a dictionary of keyword arguments.
103	When the function returns, the thread silently exits. When the function
104	terminates with an unhandled exception, a stack trace is printed and
105	then the thread exits (but other threads continue to run).
106	</dl>
107
108	<P>
109	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
110	<td><nobr><b><tt id='l2h-2692' xml:id='l2h-2692' class="function">interrupt_main</tt></b>(</nobr></td>
111	<td><var></var>)</td></tr></table></dt>
112	<dd>
113	Raise a KeyboardInterrupt in the main thread. A subthread can use this
114	function to interrupt the main thread.
115
116	<span class="versionnote">New in version 2.3.</span>
117
118	</dl>
119
120	<P>
121	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
122	<td><nobr><b><tt id='l2h-2693' xml:id='l2h-2693' class="function">exit</tt></b>(</nobr></td>
123	<td><var></var>)</td></tr></table></dt>
124	<dd>
125	Raise the <tt class="exception">SystemExit</tt> exception. When not caught, this
126	will cause the thread to exit silently.
127	</dl>
128
129	<P>
130	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
131	<td><nobr><b><tt id='l2h-2694' xml:id='l2h-2694' class="function">allocate_lock</tt></b>(</nobr></td>
132	<td><var></var>)</td></tr></table></dt>
133	<dd>
134	Return a new lock object. Methods of locks are described below. The
135	lock is initially unlocked.
136	</dl>
137
138	<P>
139	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
140	<td><nobr><b><tt id='l2h-2695' xml:id='l2h-2695' class="function">get_ident</tt></b>(</nobr></td>
141	<td><var></var>)</td></tr></table></dt>
142	<dd>
143	Return the `thread identifier' of the current thread. This is a
144	nonzero integer. Its value has no direct meaning; it is intended as a
145	magic cookie to be used e.g. to index a dictionary of thread-specific
146	data. Thread identifiers may be recycled when a thread exits and
147	another thread is created.
148	</dl>
149
150	<P>
151	Lock objects have the following methods:
152
153	<P>
154	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
155	<td><nobr><b><tt id='l2h-2696' xml:id='l2h-2696' class="method">acquire</tt></b>(</nobr></td>
156	<td><var></var><big>[</big><var>waitflag</var><big>]</big><var></var>)</td></tr></table></dt>
157	<dd>
158	Without the optional argument, this method acquires the lock
159	unconditionally, if necessary waiting until it is released by another
160	thread (only one thread at a time can acquire a lock -- that's their
161	reason for existence). If the integer
162	<var>waitflag</var> argument is present, the action depends on its
163	value: if it is zero, the lock is only acquired if it can be acquired
164	immediately without waiting, while if it is nonzero, the lock is
165	acquired unconditionally as before. The
166	return value is <code>True</code> if the lock is acquired successfully,
167	<code>False</code> if not.
168	</dl>
169
170	<P>
171	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
172	<td><nobr><b><tt id='l2h-2697' xml:id='l2h-2697' class="method">release</tt></b>(</nobr></td>
173	<td><var></var>)</td></tr></table></dt>
174	<dd>
175	Releases the lock. The lock must have been acquired earlier, but not
176	necessarily by the same thread.
177	</dl>
178
179	<P>
180	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
181	<td><nobr><b><tt id='l2h-2698' xml:id='l2h-2698' class="method">locked</tt></b>(</nobr></td>
182	<td><var></var>)</td></tr></table></dt>
183	<dd>
184	Return the status of the lock: <code>True</code> if it has been acquired by
185	some thread, <code>False</code> if not.
186	</dl>
187
188	<P>
189	<strong>Caveats:</strong>
190
191	<P>
192
193	<UL>
194	<LI>Threads interact strangely with interrupts: the
195	<tt class="exception">KeyboardInterrupt</tt> exception will be received by an
196	arbitrary thread. (When the <tt class="module"><a href="module-signal.html">signal</a></tt><a id='l2h-2702' xml:id='l2h-2702'></a>
197	module is available, interrupts always go to the main thread.)
198
199	<P>
200	</LI>
201	<LI>Calling <tt class="function">sys.exit()</tt> or raising the <tt class="exception">SystemExit</tt>
202	exception is equivalent to calling <tt class="function">exit()</tt>.
203
204	<P>
205	</LI>
206	<LI>Not all built-in functions that may block waiting for I/O allow other
207	threads to run. (The most popular ones (<tt class="function">time.sleep()</tt>,
208	<tt class="method"><var>file</var>.read()</tt>, <tt class="function">select.select()</tt>) work as
209	expected.)
210
211	<P>
212	</LI>
213	<LI>It is not possible to interrupt the <tt class="method">acquire()</tt> method on a lock
214	-- the <tt class="exception">KeyboardInterrupt</tt> exception will happen after the
215	lock has been acquired.
216
217	<P>
218	</LI>
219	<LI>When the main thread exits, it is system defined whether the other
220	threads survive. On SGI IRIX using the native thread implementation,
221	they survive. On most other systems, they are killed without
222	executing <tt class="keyword">try</tt> ... <tt class="keyword">finally</tt> clauses or executing
223	object destructors.
224	<a id='l2h-2699' xml:id='l2h-2699'></a>
225	<P>
226	</LI>
227	<LI>When the main thread exits, it does not do any of its usual cleanup
228	(except that <tt class="keyword">try</tt> ... <tt class="keyword">finally</tt> clauses are honored),
229	and the standard I/O files are not flushed.
230
231	<P>
232	</LI>
233	</UL>
234
235	<DIV CLASS="navigation">
236	<div class='online-navigation'>
237	<p></p><hr />
238	<table align="center" width="100%" cellpadding="0" cellspacing="2">
239	<tr>
240	<td class='online-navigation'><a rel="prev" title="7.3.1 Polling Objects"
241	href="poll-objects.html"><img src='../icons/previous.png'
242	border='0' height='32' alt='Previous Page' width='32' /></A></td>
243	<td class='online-navigation'><a rel="parent" title="7. Optional Operating System"
244	href="someos.html"><img src='../icons/up.png'
245	border='0' height='32' alt='Up One Level' width='32' /></A></td>
246	<td class='online-navigation'><a rel="next" title="7.5 threading "
247	href="module-threading.html"><img src='../icons/next.png'
248	border='0' height='32' alt='Next Page' width='32' /></A></td>
249	<td align="center" width="100%">Python Library Reference</td>
250	<td class='online-navigation'><a rel="contents" title="Table of Contents"
251	href="contents.html"><img src='../icons/contents.png'
252	border='0' height='32' alt='Contents' width='32' /></A></td>
253	<td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png'
254	border='0' height='32' alt='Module Index' width='32' /></a></td>
255	<td class='online-navigation'><a rel="index" title="Index"
256	href="genindex.html"><img src='../icons/index.png'
257	border='0' height='32' alt='Index' width='32' /></A></td>
258	</tr></table>
259	<div class='online-navigation'>
260	<b class="navlabel">Previous:</b>
261	<a class="sectref" rel="prev" href="poll-objects.html">7.3.1 Polling Objects</A>
262	<b class="navlabel">Up:</b>
263	<a class="sectref" rel="parent" href="someos.html">7. Optional Operating System</A>
264	<b class="navlabel">Next:</b>
265	<a class="sectref" rel="next" href="module-threading.html">7.5 threading </A>
266	</div>
267	</div>
268	<hr />
269	<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
270	</DIV>
271	<!--End of Navigation Panel-->
272	<ADDRESS>
273	See <i><a href="about.html">About this document...</a></i> for information on suggesting changes.
274	</ADDRESS>
275	</BODY>
276	</HTML>