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<?xml version='1.0'?>
<html xmlns='http://www.w3.org/1999/xhtml'
      xmlns:math='http://www.w3.org/1998/Math/MathML'
>
<head>
<title>Setup thread_alloc For Use in Multi-Threading Environment</title>
<meta http-equiv='Content-Type' content='text/html' charset='utf-8'/>
<meta name="description" id="description" content="Setup thread_alloc For Use in Multi-Threading Environment"/>
<meta name="keywords" id="keywords" content=" setup thread_alloc for use in multi-threading environment parallel num_threads in_parallel thread_num initialize syntax purpose speed restrictions example "/>
<style type='text/css'>
body { color : black }
body { background-color : white }
A:link { color : blue }
A:visited { color : purple }
A:active { color : purple }
</style>
<script type='text/javascript' language='JavaScript' src='_ta_parallel_setup_xml.js'>
</script>
</head>
<body>
<table><tr>
<td>
<a href="http://www.coin-or.org/CppAD/" target="_top"><img border="0" src="_image.gif"/></a>
</td>
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</select>
</td>
<td>ta_parallel_setup</td>
<td>
<select onchange='choose_current0(this)'>
<option>Headings-&gt;</option>
<option>Syntax</option>
<option>Purpose</option>
<option>Speed</option>
<option>num_threads</option>
<option>in_parallel</option>
<option>thread_num</option>
<option>Restrictions</option>
<option>Example</option>
</select>
</td>
</tr></table><br/>


<center><b><big><big>Setup thread_alloc For Use in Multi-Threading Environment</big></big></b></center>
<br/>
<b><big><a name="Syntax" id="Syntax">Syntax</a></big></b>

<br/>

<code><font color="blue"><span style='white-space: nowrap'>thread_alloc::parallel_setup(</span></font><i><font color="black"><span style='white-space: nowrap'>num_threads</span></font></i><font color="blue"><span style='white-space: nowrap'>,&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>in_parallel</span></font></i><font color="blue"><span style='white-space: nowrap'>,&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>thread_num</span></font></i><font color="blue"><span style='white-space: nowrap'>)<br/>
</span></font></code>
<br/>
<b><big><a name="Purpose" id="Purpose">Purpose</a></big></b>
<br/>
By default there is only one thread and all execution is in sequential mode,
i.e., multiple threads are not sharing the same memory; i.e.
not in parallel mode.

<br/>
<br/>
<b><big><a name="Speed" id="Speed">Speed</a></big></b>
<br/>
It should be faster, even when 
<code><i><font color="black"><span style='white-space: nowrap'>num_thread</span></font></i></code>
 is equal to one,
for <code><font color="blue">thread_alloc</font></code> to hold onto memory.
This can be accomplished using the function call

<code><font color="blue"><span style='white-space: nowrap'><br/>
&#xA0;&#xA0;&#xA0;&#xA0;&#xA0;thread_alloc::hold_memory(true)<br/>
</span></font></code>
see <a href="ta_hold_memory.xml" target="_top"><span style='white-space: nowrap'>hold_memory</span></a>
.

<br/>
<br/>
<b><big><a name="num_threads" id="num_threads">num_threads</a></big></b>
<br/>
This argument has prototype

<code><font color="blue"><span style='white-space: nowrap'><br/>
&#xA0;&#xA0;&#xA0;&#xA0;&#xA0;size_t&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>num_threads</span></font></i><font color="blue"><span style='white-space: nowrap'><br/>
</span></font></code>
and must be greater than zero.
It specifies the number of threads that are sharing memory.
The case 
<code><i><font color="black"><span style='white-space: nowrap'>num_threads</span></font></i><font color="blue"><span style='white-space: nowrap'>&#xA0;==&#xA0;1</span></font></code>
 is a special case that is 
used to terminate a multi-threading environment.

<br/>
<br/>
<b><big><a name="in_parallel" id="in_parallel">in_parallel</a></big></b>
<br/>
This function has prototype

<code><font color="blue"><span style='white-space: nowrap'><br/>
&#xA0;&#xA0;&#xA0;&#xA0;&#xA0;bool&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>in_parallel</span></font></i><font color="blue"><span style='white-space: nowrap'>(void)&#xA0;<br/>
</span></font></code>
It must return <code><font color="blue">true</font></code> if there is more than one thread
currently executing.
Otherwise it can return false.
<code><span style='white-space: nowrap'><br/>
<br/>
</span></code>In the special case where 
<code><i><font color="black"><span style='white-space: nowrap'>num_threads</span></font></i><font color="blue"><span style='white-space: nowrap'>&#xA0;==&#xA0;1</span></font></code>
,
the routine 
<code><i><font color="black"><span style='white-space: nowrap'>in_parallel</span></font></i></code>
 is not used.

<br/>
<br/>
<b><big><a name="thread_num" id="thread_num">thread_num</a></big></b>
<br/>
This function has prototype

<code><font color="blue"><span style='white-space: nowrap'><br/>
&#xA0;&#xA0;&#xA0;&#xA0;&#xA0;size_t&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>thread_num</span></font></i><font color="blue"><span style='white-space: nowrap'>(void)&#xA0;<br/>
</span></font></code>
It must return a thread number that uniquely identifies the
currently executing thread. 
Furthermore

<code><font color="blue"><span style='white-space: nowrap'><br/>
&#xA0;&#xA0;&#xA0;&#xA0;&#xA0;0&#xA0;&lt;=&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>thread_num</span></font></i><font color="blue"><span style='white-space: nowrap'>()&#xA0;&lt;&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>num_threads</span></font></i><font color="blue"><span style='white-space: nowrap'><br/>
</span></font></code>
.
In the special case where 
<code><i><font color="black"><span style='white-space: nowrap'>num_threads</span></font></i><font color="blue"><span style='white-space: nowrap'>&#xA0;==&#xA0;1</span></font></code>
,
the routine 
<code><i><font color="black"><span style='white-space: nowrap'>thread_num</span></font></i></code>
 is not used.
<code><span style='white-space: nowrap'><br/>
<br/>
</span></code>Note that this function is called by other routines so,
as soon as a new thread is executing,
one must be certain that 
<code><i><font color="black"><span style='white-space: nowrap'>thread_num()</span></font></i></code>
 will
work for that thread.

<br/>
<br/>
<b><big><a name="Restrictions" id="Restrictions">Restrictions</a></big></b>
<br/>
The function <code><font color="blue">parallel_setup</font></code> must be called before 
the program enters <a href="ta_in_parallel.xml" target="_top"><span style='white-space: nowrap'>parallel</span></a>
 execution mode.
In addition, this function cannot be called while in parallel mode.

<br/>
<br/>
<b><big><a name="Example" id="Example">Example</a></big></b>
<br/>
The files 
<a href="simple_ad_openmp.cpp.xml" target="_top"><span style='white-space: nowrap'>simple_ad_openmp.cpp</span></a>
, 
<a href="simple_ad_bthread.cpp.xml" target="_top"><span style='white-space: nowrap'>simple_ad_bthread.cpp</span></a>
, and
<a href="simple_ad_pthread.cpp.xml" target="_top"><span style='white-space: nowrap'>simple_ad_pthread.cpp</span></a>
, 
contain examples and tests that use this function.   


<hr/>Input File: cppad/thread_alloc.hpp

</body>
</html>