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<a href="#pub-methods">Public Member Functions</a> |
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<div class="title">wxSemaphore Class Reference<div class="ingroups"><a class="el" href="group__group__class__threading.html">Threading</a></div></div> </div>
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<p><code>#include <wx/thread.h></code></p>
<a name="details" id="details"></a><h2 class="groupheader">Detailed Description</h2>
<div class="textblock"><p><a class="el" href="classwx_semaphore.html" title="wxSemaphore is a counter limiting the number of threads concurrently accessing a shared resource...">wxSemaphore</a> is a counter limiting the number of threads concurrently accessing a shared resource. </p>
<p>This counter is always between 0 and the maximum value specified during the semaphore creation. When the counter is strictly greater than 0, a call to <a class="el" href="classwx_semaphore.html#a4a54b5fbb2b80b7ca3b8da55e8fa790c" title="Wait indefinitely until the semaphore count becomes strictly positive and then decrement it and retur...">wxSemaphore::Wait()</a> returns immediately and decrements the counter. As soon as it reaches 0, any subsequent calls to <a class="el" href="classwx_semaphore.html#a4a54b5fbb2b80b7ca3b8da55e8fa790c" title="Wait indefinitely until the semaphore count becomes strictly positive and then decrement it and retur...">wxSemaphore::Wait</a> block and only return when the semaphore counter becomes strictly positive again as the result of calling <a class="el" href="classwx_semaphore.html#af258c7e7a626fec8a9fc3ff718c960d6" title="Increments the semaphore count and signals one of the waiting threads in an atomic way...">wxSemaphore::Post</a> which increments the counter.</p>
<p>In general, semaphores are useful to restrict access to a shared resource which can only be accessed by some fixed number of clients at the same time. For example, when modeling a hotel reservation system a semaphore with the counter equal to the total number of available rooms could be created. Each time a room is reserved, the semaphore should be acquired by calling <a class="el" href="classwx_semaphore.html#a4a54b5fbb2b80b7ca3b8da55e8fa790c" title="Wait indefinitely until the semaphore count becomes strictly positive and then decrement it and retur...">wxSemaphore::Wait</a> and each time a room is freed it should be released by calling <a class="el" href="classwx_semaphore.html#af258c7e7a626fec8a9fc3ff718c960d6" title="Increments the semaphore count and signals one of the waiting threads in an atomic way...">wxSemaphore::Post</a>.</p>
<h2></h2>
<div><span class="lib">Library:</span>  <span class="lib_text"><a class="el" href="page_libs.html#page_libs_wxbase">wxBase</a></span></div><div><span class="category">Category:</span>  <span class="category_text"><a class="el" href="group__group__class__threading.html">Threading</a></span></div> </div><table class="memberdecls">
<tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="pub-methods"></a>
Public Member Functions</h2></td></tr>
<tr class="memitem:ac3cd6a6d45363c878f366a128294e22c"><td class="memItemLeft" align="right" valign="top"> </td><td class="memItemRight" valign="bottom"><a class="el" href="classwx_semaphore.html#ac3cd6a6d45363c878f366a128294e22c">wxSemaphore</a> (int initialcount=0, int maxcount=0)</td></tr>
<tr class="memdesc:ac3cd6a6d45363c878f366a128294e22c"><td class="mdescLeft"> </td><td class="mdescRight">Specifying a <em>maxcount</em> of 0 actually makes <a class="el" href="classwx_semaphore.html" title="wxSemaphore is a counter limiting the number of threads concurrently accessing a shared resource...">wxSemaphore</a> behave as if there is no upper limit. <a href="#ac3cd6a6d45363c878f366a128294e22c"></a><br/></td></tr>
<tr class="separator:ac3cd6a6d45363c878f366a128294e22c"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a6192d18717c270bed9ec3a7e7842ef3f"><td class="memItemLeft" align="right" valign="top"> </td><td class="memItemRight" valign="bottom"><a class="el" href="classwx_semaphore.html#a6192d18717c270bed9ec3a7e7842ef3f">~wxSemaphore</a> ()</td></tr>
<tr class="memdesc:a6192d18717c270bed9ec3a7e7842ef3f"><td class="mdescLeft"> </td><td class="mdescRight">Destructor is not virtual, don't use this class polymorphically. <a href="#a6192d18717c270bed9ec3a7e7842ef3f"></a><br/></td></tr>
<tr class="separator:a6192d18717c270bed9ec3a7e7842ef3f"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:af258c7e7a626fec8a9fc3ff718c960d6"><td class="memItemLeft" align="right" valign="top"><a class="el" href="interface_2wx_2thread_8h.html#a47100c8fbaa57b192696bec84197398e">wxSemaError</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classwx_semaphore.html#af258c7e7a626fec8a9fc3ff718c960d6">Post</a> ()</td></tr>
<tr class="memdesc:af258c7e7a626fec8a9fc3ff718c960d6"><td class="mdescLeft"> </td><td class="mdescRight">Increments the semaphore count and signals one of the waiting threads in an atomic way. <a href="#af258c7e7a626fec8a9fc3ff718c960d6"></a><br/></td></tr>
<tr class="separator:af258c7e7a626fec8a9fc3ff718c960d6"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a578840a5c04cea87b0121c8e43d480a2"><td class="memItemLeft" align="right" valign="top"><a class="el" href="interface_2wx_2thread_8h.html#a47100c8fbaa57b192696bec84197398e">wxSemaError</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classwx_semaphore.html#a578840a5c04cea87b0121c8e43d480a2">TryWait</a> ()</td></tr>
<tr class="memdesc:a578840a5c04cea87b0121c8e43d480a2"><td class="mdescLeft"> </td><td class="mdescRight">Same as <a class="el" href="classwx_semaphore.html#a4a54b5fbb2b80b7ca3b8da55e8fa790c" title="Wait indefinitely until the semaphore count becomes strictly positive and then decrement it and retur...">Wait()</a>, but returns immediately. <a href="#a578840a5c04cea87b0121c8e43d480a2"></a><br/></td></tr>
<tr class="separator:a578840a5c04cea87b0121c8e43d480a2"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a4a54b5fbb2b80b7ca3b8da55e8fa790c"><td class="memItemLeft" align="right" valign="top"><a class="el" href="interface_2wx_2thread_8h.html#a47100c8fbaa57b192696bec84197398e">wxSemaError</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classwx_semaphore.html#a4a54b5fbb2b80b7ca3b8da55e8fa790c">Wait</a> ()</td></tr>
<tr class="memdesc:a4a54b5fbb2b80b7ca3b8da55e8fa790c"><td class="mdescLeft"> </td><td class="mdescRight">Wait indefinitely until the semaphore count becomes strictly positive and then decrement it and return. <a href="#a4a54b5fbb2b80b7ca3b8da55e8fa790c"></a><br/></td></tr>
<tr class="separator:a4a54b5fbb2b80b7ca3b8da55e8fa790c"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a4bef53c549148e807fbf729129ba7572"><td class="memItemLeft" align="right" valign="top"><a class="el" href="interface_2wx_2thread_8h.html#a47100c8fbaa57b192696bec84197398e">wxSemaError</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classwx_semaphore.html#a4bef53c549148e807fbf729129ba7572">WaitTimeout</a> (unsigned long timeout_millis)</td></tr>
<tr class="memdesc:a4bef53c549148e807fbf729129ba7572"><td class="mdescLeft"> </td><td class="mdescRight">Same as <a class="el" href="classwx_semaphore.html#a4a54b5fbb2b80b7ca3b8da55e8fa790c" title="Wait indefinitely until the semaphore count becomes strictly positive and then decrement it and retur...">Wait()</a>, but with a timeout limit. <a href="#a4bef53c549148e807fbf729129ba7572"></a><br/></td></tr>
<tr class="separator:a4bef53c549148e807fbf729129ba7572"><td class="memSeparator" colspan="2"> </td></tr>
</table>
<h2 class="groupheader">Constructor & Destructor Documentation</h2>
<a class="anchor" id="ac3cd6a6d45363c878f366a128294e22c"></a>
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<td class="memname">wxSemaphore::wxSemaphore </td>
<td>(</td>
<td class="paramtype">int </td>
<td class="paramname"><em>initialcount</em> = <code>0</code>, </td>
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<td class="paramkey"></td>
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<td class="paramtype">int </td>
<td class="paramname"><em>maxcount</em> = <code>0</code> </td>
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<td>)</td>
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<p>Specifying a <em>maxcount</em> of 0 actually makes <a class="el" href="classwx_semaphore.html" title="wxSemaphore is a counter limiting the number of threads concurrently accessing a shared resource...">wxSemaphore</a> behave as if there is no upper limit. </p>
<p>If <em>maxcount</em> is 1, the semaphore behaves almost as a mutex (but unlike a mutex it can be released by a thread different from the one which acquired it).</p>
<p><em>initialcount</em> is the initial value of the semaphore which must be between 0 and <em>maxcount</em> (if it is not set to 0). </p>
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<td class="memname">wxSemaphore::~wxSemaphore </td>
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<td class="paramname"></td><td>)</td>
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<p>Destructor is not virtual, don't use this class polymorphically. </p>
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<h2 class="groupheader">Member Function Documentation</h2>
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<td class="memname"><a class="el" href="interface_2wx_2thread_8h.html#a47100c8fbaa57b192696bec84197398e">wxSemaError</a> wxSemaphore::Post </td>
<td>(</td>
<td class="paramname"></td><td>)</td>
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<p>Increments the semaphore count and signals one of the waiting threads in an atomic way. </p>
<p>Returns <em>wxSEMA_OVERFLOW</em> if the count would increase the counter past the maximum.</p>
<dl class="section return"><dt>Returns</dt><dd>One of:<ul>
<li>wxSEMA_NO_ERROR: There was no error.</li>
<li>wxSEMA_INVALID : Semaphore hasn't been initialized successfully.</li>
<li>wxSEMA_OVERFLOW: <a class="el" href="classwx_semaphore.html#af258c7e7a626fec8a9fc3ff718c960d6" title="Increments the semaphore count and signals one of the waiting threads in an atomic way...">Post()</a> would increase counter past the max.</li>
<li>wxSEMA_MISC_ERROR: Miscellaneous error. </li>
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</dd></dl>
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<td class="memname"><a class="el" href="interface_2wx_2thread_8h.html#a47100c8fbaa57b192696bec84197398e">wxSemaError</a> wxSemaphore::TryWait </td>
<td>(</td>
<td class="paramname"></td><td>)</td>
<td></td>
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<p>Same as <a class="el" href="classwx_semaphore.html#a4a54b5fbb2b80b7ca3b8da55e8fa790c" title="Wait indefinitely until the semaphore count becomes strictly positive and then decrement it and retur...">Wait()</a>, but returns immediately. </p>
<dl class="section return"><dt>Returns</dt><dd>One of:<ul>
<li>wxSEMA_NO_ERROR: There was no error.</li>
<li>wxSEMA_INVALID: Semaphore hasn't been initialized successfully.</li>
<li>wxSEMA_BUSY: Returned by <a class="el" href="classwx_semaphore.html#a578840a5c04cea87b0121c8e43d480a2" title="Same as Wait(), but returns immediately.">TryWait()</a> if <a class="el" href="classwx_semaphore.html#a4a54b5fbb2b80b7ca3b8da55e8fa790c" title="Wait indefinitely until the semaphore count becomes strictly positive and then decrement it and retur...">Wait()</a> would block, i.e. the count is zero.</li>
<li>wxSEMA_MISC_ERROR: Miscellaneous error. </li>
</ul>
</dd></dl>
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<td class="memname"><a class="el" href="interface_2wx_2thread_8h.html#a47100c8fbaa57b192696bec84197398e">wxSemaError</a> wxSemaphore::Wait </td>
<td>(</td>
<td class="paramname"></td><td>)</td>
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<p>Wait indefinitely until the semaphore count becomes strictly positive and then decrement it and return. </p>
<dl class="section return"><dt>Returns</dt><dd>One of:<ul>
<li>wxSEMA_NO_ERROR: There was no error.</li>
<li>wxSEMA_INVALID: Semaphore hasn't been initialized successfully.</li>
<li>wxSEMA_MISC_ERROR: Miscellaneous error. </li>
</ul>
</dd></dl>
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<td class="memname"><a class="el" href="interface_2wx_2thread_8h.html#a47100c8fbaa57b192696bec84197398e">wxSemaError</a> wxSemaphore::WaitTimeout </td>
<td>(</td>
<td class="paramtype">unsigned long </td>
<td class="paramname"><em>timeout_millis</em></td><td>)</td>
<td></td>
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<p>Same as <a class="el" href="classwx_semaphore.html#a4a54b5fbb2b80b7ca3b8da55e8fa790c" title="Wait indefinitely until the semaphore count becomes strictly positive and then decrement it and retur...">Wait()</a>, but with a timeout limit. </p>
<dl class="section return"><dt>Returns</dt><dd>One of:<ul>
<li>wxSEMA_NO_ERROR: There was no error.</li>
<li>wxSEMA_INVALID: Semaphore hasn't been initialized successfully.</li>
<li>wxSEMA_TIMEOUT: Timeout occurred without receiving semaphore.</li>
<li>wxSEMA_MISC_ERROR: Miscellaneous error. </li>
</ul>
</dd></dl>
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