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<hr><h1>ost::Semaphore Class Reference</h1>A semaphore is generally used as a synchronization object between multiple threads or to protect a limited and finite resource such as a memory or thread pool. <a class="el" href="classost_1_1_semaphore.html">Semaphore</a> counter for thread synchronization.
<a href="#_details">More...</a>
<p>
<code>#include <<a class="el" href="thread_8h-source.html">thread.h</a>></code>
<p>
<a href="classost_1_1_semaphore-members.html">List of all members.</a><table border=0 cellpadding=0 cellspacing=0>
<tr><td colspan=2><br><h2>Public Methods</h2></td></tr>
<tr><td nowrap align=right valign=top> </td><td valign=bottom><a class="el" href="classost_1_1_semaphore.html#a0">Semaphore</a> (size_t resource=0)</td></tr>
<tr><td> </td><td><font size=-1><em>The initial value of the semaphore can be specified.</em> <a href="#a0">More...</a><em></em></font><br><br></td></tr>
<tr><td nowrap align=right valign=top>virtual </td><td valign=bottom><a class="el" href="classost_1_1_semaphore.html#a1">~Semaphore</a> ()</td></tr>
<tr><td> </td><td><font size=-1><em>Destroying a semaphore also removes any system resources associated with it.</em> <a href="#a1">More...</a><em></em></font><br><br></td></tr>
<tr><td nowrap align=right valign=top>void </td><td valign=bottom><a class="el" href="classost_1_1_semaphore.html#a2">Wait</a> (void)</td></tr>
<tr><td> </td><td><font size=-1><em>Wait is used to keep a thread held until the semaphore counter is greater than 0.</em> <a href="#a2">More...</a><em></em></font><br><br></td></tr>
<tr><td nowrap align=right valign=top>bool </td><td valign=bottom><a class="el" href="classost_1_1_semaphore.html#a3">TryWait</a> (void)</td></tr>
<tr><td> </td><td><font size=-1><em>TryWait is a non-blocking variant of Wait.</em> <a href="#a3">More...</a><em></em></font><br><br></td></tr>
<tr><td nowrap align=right valign=top>void </td><td valign=bottom><a class="el" href="classost_1_1_semaphore.html#a4">Post</a> (void)</td></tr>
<tr><td> </td><td><font size=-1><em>Posting to a semaphore increments its current value and releases the first thread waiting for the semaphore if it is currently at 0.</em> <a href="#a4">More...</a><em></em></font><br><br></td></tr>
<tr><td nowrap align=right valign=top>int </td><td valign=bottom><a class="el" href="classost_1_1_semaphore.html#a5">getValue</a> (void)</td></tr>
<tr><td> </td><td><font size=-1><em>Get the current value of a semaphore.</em> <a href="#a5">More...</a><em></em></font><br><br></td></tr>
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<hr><a name="_details"></a><h2>Detailed Description</h2>
A semaphore is generally used as a synchronization object between multiple threads or to protect a limited and finite resource such as a memory or thread pool. <a class="el" href="classost_1_1_semaphore.html">Semaphore</a> counter for thread synchronization.
<p>
The semaphore has a counter which only permits access by one or more threads when the value of the semaphore is non-zero. Each access reduces the current value of the semaphore by 1. One or more threads can wait on a semaphore until it is no longer 0, and hence the semaphore can be used as a simple thread synchronization object to enable one thread to pause others until the thread is ready or has provided data for them. Semaphores are typically used as a counter for protecting or limiting concurrent access to a given resource, such as to permitting at most "x" number of threads to use resource "y", for example.
<p>
<dl compact><dt><b>
Author: </b><dd>
David Sugar <<a href="mailto:dyfet@ostel.com">dyfet@ostel.com</a>> </dl>
<p>
<hr><h2>Constructor & Destructor Documentation</h2>
<a name="a0" doxytag="ost::Semaphore::Semaphore"></a><p>
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<td class="md">
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<td class="md" nowrap valign="top"> ost::Semaphore::Semaphore </td>
<td class="md">( </td>
<td class="md">size_t</td>
<td class="mdname1"> <em>resource</em> = 0 </td>
<td class="md">) </td>
<td class="md"></td>
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</td>
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<td>
</td>
<td>
<p>
The initial value of the semaphore can be specified.
<p>
An initial value is often used When used to lock a finite resource or to specify the maximum number of thread instances that can access a specified resource.<dl compact><dt><b>
Parameters: </b><dd>
<table border=0 cellspacing=2 cellpadding=0>
<tr><td valign=top><em>resource
</em> </td><td>
specify initial resource count or 0 default. </td></tr>
</table>
</dl> </td>
</tr>
</table>
<a name="a1" doxytag="ost::Semaphore::~Semaphore"></a><p>
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<td class="md">
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<td class="md" nowrap valign="top"> virtual ost::Semaphore::~Semaphore </td>
<td class="md">( </td>
<td class="mdname1"> </td>
<td class="md">) </td>
<td class="md"><code> [virtual]</code></td>
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</td>
</tr>
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<td>
</td>
<td>
<p>
Destroying a semaphore also removes any system resources associated with it.
<p>
If a semaphore has threads currently waiting on it, those threads will all continue when a semaphore is destroyed. </td>
</tr>
</table>
<hr><h2>Member Function Documentation</h2>
<a name="a4" doxytag="ost::Semaphore::Post"></a><p>
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<td class="md">
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<td class="md" nowrap valign="top"> void ost::Semaphore::Post </td>
<td class="md">( </td>
<td class="md">void</td>
<td class="mdname1"> </td>
<td class="md">) </td>
<td class="md"></td>
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</td>
</tr>
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<td>
</td>
<td>
<p>
Posting to a semaphore increments its current value and releases the first thread waiting for the semaphore if it is currently at 0.
<p>
Interestingly, there is no support to increment a semaphore by any value greater than 1 to release multiple waiting threads in either pthread or the win32 API. Hence, if one wants to release a semaphore to enable multiple threads to execute, one must perform multiple post operations.
<p>
<dl compact><dt><b>
See also: </b><dd>
<a class="el" href="classost_1_1_semaphore.html#a2">Wait</a> </dl> </td>
</tr>
</table>
<a name="a3" doxytag="ost::Semaphore::TryWait"></a><p>
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<td class="md">
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<td class="md" nowrap valign="top"> bool ost::Semaphore::TryWait </td>
<td class="md">( </td>
<td class="md">void</td>
<td class="mdname1"> </td>
<td class="md">) </td>
<td class="md"></td>
</tr>
</table>
</td>
</tr>
</table>
<table cellspacing=5 cellpadding=0 border=0>
<tr>
<td>
</td>
<td>
<p>
TryWait is a non-blocking variant of Wait.
<p>
If the semaphore counter is greater than 0, then the thread is accepted and the semaphore counter is decreased. If the semaphore counter is 0 TryWait returns immediately with false.
<p>
<dl compact><dt><b>
Returns: </b><dd>
true if thread is accepted otherwise false</dl><dl compact><dt><b>
See also: </b><dd>
<a class="el" href="classost_1_1_semaphore.html#a2">Wait</a> , <a class="el" href="classost_1_1_semaphore.html#a4">Post</a> </dl> </td>
</tr>
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<a name="a2" doxytag="ost::Semaphore::Wait"></a><p>
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<tr>
<td class="md">
<table cellpadding="0" cellspacing="0" border="0">
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<td class="md" nowrap valign="top"> void ost::Semaphore::Wait </td>
<td class="md">( </td>
<td class="md">void</td>
<td class="mdname1"> </td>
<td class="md">) </td>
<td class="md"></td>
</tr>
</table>
</td>
</tr>
</table>
<table cellspacing=5 cellpadding=0 border=0>
<tr>
<td>
</td>
<td>
<p>
Wait is used to keep a thread held until the semaphore counter is greater than 0.
<p>
If the current thread is held, then another thread must increment the semaphore. Once the thread is accepted, the semaphore is automatically decremented, and the thread continues execution.
<p>
The pthread semaphore object does not support a timed "wait", and hence to maintain consistancy, neither the posix nor win32 source trees support "timed" semaphore objects.
<p>
<dl compact><dt><b>
See also: </b><dd>
<a class="el" href="classost_1_1_semaphore.html#a4">Post</a> </dl> </td>
</tr>
</table>
<a name="a5" doxytag="ost::Semaphore::getValue"></a><p>
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<td class="md">
<table cellpadding="0" cellspacing="0" border="0">
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<td class="md" nowrap valign="top"> int ost::Semaphore::getValue </td>
<td class="md">( </td>
<td class="md">void</td>
<td class="mdname1"> </td>
<td class="md">) </td>
<td class="md"></td>
</tr>
</table>
</td>
</tr>
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<table cellspacing=5 cellpadding=0 border=0>
<tr>
<td>
</td>
<td>
<p>
Get the current value of a semaphore.
<p>
<dl compact><dt><b>
Returns: </b><dd>
current value. </dl> </td>
</tr>
</table>
<hr>The documentation for this class was generated from the following file:<ul>
<li><a class="el" href="thread_8h-source.html">thread.h</a></ul>
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