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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<li class="navelem"><b>mysqlpp</b></li><li class="navelem"><a class="el" href="classmysqlpp_1_1ConnectionPool.html">ConnectionPool</a></li> </ul>
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</div><!-- top -->
<div class="header">
<div class="summary">
<a href="#nested-classes">Classes</a> |
<a href="#pub-methods">Public Member Functions</a> |
<a href="#pro-methods">Protected Member Functions</a> |
<a href="classmysqlpp_1_1ConnectionPool-members.html">List of all members</a> </div>
<div class="headertitle">
<div class="title">mysqlpp::ConnectionPool Class Reference<span class="mlabels"><span class="mlabel">abstract</span></span></div> </div>
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<div class="contents">
<p>Manages a pool of connections for programs that need more than one <a class="el" href="classmysqlpp_1_1Connection.html" title="Manages the connection to the database server.">Connection</a> object at a time, but can't predict how many they need in advance.
<a href="classmysqlpp_1_1ConnectionPool.html#details">More...</a></p>
<p><code>#include <<a class="el" href="cpool_8h_source.html">cpool.h</a>></code></p>
<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:acc1262db33d586284651825ff076a8d7"><td class="memItemLeft" align="right" valign="top"><a id="acc1262db33d586284651825ff076a8d7"></a>
 </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1ConnectionPool.html#acc1262db33d586284651825ff076a8d7">ConnectionPool</a> ()</td></tr>
<tr class="memdesc:acc1262db33d586284651825ff076a8d7"><td class="mdescLeft"> </td><td class="mdescRight">Create empty pool. <br /></td></tr>
<tr class="separator:acc1262db33d586284651825ff076a8d7"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a2cee954229416e24da07f5e208b35b09"><td class="memItemLeft" align="right" valign="top">virtual </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1ConnectionPool.html#a2cee954229416e24da07f5e208b35b09">~ConnectionPool</a> ()</td></tr>
<tr class="memdesc:a2cee954229416e24da07f5e208b35b09"><td class="mdescLeft"> </td><td class="mdescRight">Destroy object. <a href="#a2cee954229416e24da07f5e208b35b09">More...</a><br /></td></tr>
<tr class="separator:a2cee954229416e24da07f5e208b35b09"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:ac7f3bd443b9a70fb21ce86fa7ced880e"><td class="memItemLeft" align="right" valign="top"><a id="ac7f3bd443b9a70fb21ce86fa7ced880e"></a>
bool </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1ConnectionPool.html#ac7f3bd443b9a70fb21ce86fa7ced880e">empty</a> () const</td></tr>
<tr class="memdesc:ac7f3bd443b9a70fb21ce86fa7ced880e"><td class="mdescLeft"> </td><td class="mdescRight">Returns true if pool is empty. <br /></td></tr>
<tr class="separator:ac7f3bd443b9a70fb21ce86fa7ced880e"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a4f9844f2c57c9f51f1b5a2b8a996ee15"><td class="memItemLeft" align="right" valign="top">virtual <a class="el" href="classmysqlpp_1_1Connection.html">Connection</a> * </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1ConnectionPool.html#a4f9844f2c57c9f51f1b5a2b8a996ee15">exchange</a> (const <a class="el" href="classmysqlpp_1_1Connection.html">Connection</a> *pc)</td></tr>
<tr class="memdesc:a4f9844f2c57c9f51f1b5a2b8a996ee15"><td class="mdescLeft"> </td><td class="mdescRight">Return a defective connection to the pool and get a new one back. <a href="#a4f9844f2c57c9f51f1b5a2b8a996ee15">More...</a><br /></td></tr>
<tr class="separator:a4f9844f2c57c9f51f1b5a2b8a996ee15"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:acbf56ee86ef66b3ebdf02adde5908776"><td class="memItemLeft" align="right" valign="top">virtual <a class="el" href="classmysqlpp_1_1Connection.html">Connection</a> * </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1ConnectionPool.html#acbf56ee86ef66b3ebdf02adde5908776">grab</a> ()</td></tr>
<tr class="memdesc:acbf56ee86ef66b3ebdf02adde5908776"><td class="mdescLeft"> </td><td class="mdescRight">Grab a free connection from the pool. <a href="#acbf56ee86ef66b3ebdf02adde5908776">More...</a><br /></td></tr>
<tr class="separator:acbf56ee86ef66b3ebdf02adde5908776"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:ac51a7a63ce4d8825c3f7b05f4b8bfe68"><td class="memItemLeft" align="right" valign="top">virtual void </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1ConnectionPool.html#ac51a7a63ce4d8825c3f7b05f4b8bfe68">release</a> (const <a class="el" href="classmysqlpp_1_1Connection.html">Connection</a> *pc)</td></tr>
<tr class="memdesc:ac51a7a63ce4d8825c3f7b05f4b8bfe68"><td class="mdescLeft"> </td><td class="mdescRight">Return a connection to the pool. <a href="#ac51a7a63ce4d8825c3f7b05f4b8bfe68">More...</a><br /></td></tr>
<tr class="separator:ac51a7a63ce4d8825c3f7b05f4b8bfe68"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:aae75febe979da2d4a3335c46438f3d33"><td class="memItemLeft" align="right" valign="top">void </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1ConnectionPool.html#aae75febe979da2d4a3335c46438f3d33">remove</a> (const <a class="el" href="classmysqlpp_1_1Connection.html">Connection</a> *pc)</td></tr>
<tr class="memdesc:aae75febe979da2d4a3335c46438f3d33"><td class="mdescLeft"> </td><td class="mdescRight">Removes the given connection from the pool. <a href="#aae75febe979da2d4a3335c46438f3d33">More...</a><br /></td></tr>
<tr class="separator:aae75febe979da2d4a3335c46438f3d33"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:aac4d50bb5c603efec4b8d7e0a3e8a164"><td class="memItemLeft" align="right" valign="top">virtual <a class="el" href="classmysqlpp_1_1Connection.html">Connection</a> * </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1ConnectionPool.html#aac4d50bb5c603efec4b8d7e0a3e8a164">safe_grab</a> ()</td></tr>
<tr class="memdesc:aac4d50bb5c603efec4b8d7e0a3e8a164"><td class="mdescLeft"> </td><td class="mdescRight">Grab a free connection from the pool, testing that it's connected before returning it. <a href="#aac4d50bb5c603efec4b8d7e0a3e8a164">More...</a><br /></td></tr>
<tr class="separator:aac4d50bb5c603efec4b8d7e0a3e8a164"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:ac410ed5cb3032aed048fb3a275629654"><td class="memItemLeft" align="right" valign="top"><a id="ac410ed5cb3032aed048fb3a275629654"></a>
void </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1ConnectionPool.html#ac410ed5cb3032aed048fb3a275629654">shrink</a> ()</td></tr>
<tr class="memdesc:ac410ed5cb3032aed048fb3a275629654"><td class="mdescLeft"> </td><td class="mdescRight">Remove all unused connections from the pool. <br /></td></tr>
<tr class="separator:ac410ed5cb3032aed048fb3a275629654"><td class="memSeparator" colspan="2"> </td></tr>
</table><table class="memberdecls">
<tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="pro-methods"></a>
Protected Member Functions</h2></td></tr>
<tr class="memitem:a981e1b1715de2daea9f6b10bdcbb5915"><td class="memItemLeft" align="right" valign="top">void </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1ConnectionPool.html#a981e1b1715de2daea9f6b10bdcbb5915">clear</a> (bool all=true)</td></tr>
<tr class="memdesc:a981e1b1715de2daea9f6b10bdcbb5915"><td class="mdescLeft"> </td><td class="mdescRight">Drains the pool, freeing all allocated memory. <a href="#a981e1b1715de2daea9f6b10bdcbb5915">More...</a><br /></td></tr>
<tr class="separator:a981e1b1715de2daea9f6b10bdcbb5915"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:af755c7e11b92bbab0e88ab3e9c88f0fd"><td class="memItemLeft" align="right" valign="top">virtual <a class="el" href="classmysqlpp_1_1Connection.html">Connection</a> * </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1ConnectionPool.html#af755c7e11b92bbab0e88ab3e9c88f0fd">create</a> ()=0</td></tr>
<tr class="memdesc:af755c7e11b92bbab0e88ab3e9c88f0fd"><td class="mdescLeft"> </td><td class="mdescRight">Create a new connection. <a href="#af755c7e11b92bbab0e88ab3e9c88f0fd">More...</a><br /></td></tr>
<tr class="separator:af755c7e11b92bbab0e88ab3e9c88f0fd"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a3dae30e24dd6967e4e427fa69dbc2105"><td class="memItemLeft" align="right" valign="top">virtual void </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1ConnectionPool.html#a3dae30e24dd6967e4e427fa69dbc2105">destroy</a> (<a class="el" href="classmysqlpp_1_1Connection.html">Connection</a> *)=0</td></tr>
<tr class="memdesc:a3dae30e24dd6967e4e427fa69dbc2105"><td class="mdescLeft"> </td><td class="mdescRight">Destroy a connection. <a href="#a3dae30e24dd6967e4e427fa69dbc2105">More...</a><br /></td></tr>
<tr class="separator:a3dae30e24dd6967e4e427fa69dbc2105"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a8a5ba414a5b02c48d64501c25b64a656"><td class="memItemLeft" align="right" valign="top">virtual unsigned int </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1ConnectionPool.html#a8a5ba414a5b02c48d64501c25b64a656">max_idle_time</a> ()=0</td></tr>
<tr class="memdesc:a8a5ba414a5b02c48d64501c25b64a656"><td class="mdescLeft"> </td><td class="mdescRight">Returns the maximum number of seconds a connection is able to remain idle before it is dropped. <a href="#a8a5ba414a5b02c48d64501c25b64a656">More...</a><br /></td></tr>
<tr class="separator:a8a5ba414a5b02c48d64501c25b64a656"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a852e802aa80a2e608926760a1d9b4591"><td class="memItemLeft" align="right" valign="top"><a id="a852e802aa80a2e608926760a1d9b4591"></a>
size_t </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1ConnectionPool.html#a852e802aa80a2e608926760a1d9b4591">size</a> () const</td></tr>
<tr class="memdesc:a852e802aa80a2e608926760a1d9b4591"><td class="mdescLeft"> </td><td class="mdescRight">Returns the current size of the internal connection pool. <br /></td></tr>
<tr class="separator:a852e802aa80a2e608926760a1d9b4591"><td class="memSeparator" colspan="2"> </td></tr>
</table>
<a name="details" id="details"></a><h2 class="groupheader">Detailed Description</h2>
<div class="textblock"><p>Manages a pool of connections for programs that need more than one <a class="el" href="classmysqlpp_1_1Connection.html" title="Manages the connection to the database server.">Connection</a> object at a time, but can't predict how many they need in advance. </p>
<p>This class is useful in programs that need to make multiple simultaneous queries on the database; this requires multiple <a class="el" href="classmysqlpp_1_1Connection.html" title="Manages the connection to the database server.">Connection</a> objects due to a hard limitation of the underlying C API. <a class="el" href="classmysqlpp_1_1Connection.html" title="Manages the connection to the database server.">Connection</a> pools are most useful in multithreaded programs, but it can be helpful to have one in a single-threaded program as well. Sometimes it's necessary to get more data from the server while in the middle of processing data from an earlier query; this requires multiple connections. Whether you use a pool or manage connections yourself is up to you, but realize that this class takes care of a lot of subtle details for you that aren't obvious.</p>
<p>The pool's policy for connection reuse is to always return the <em>most</em> recently used connection that's not being used right now. This ensures that excess connections don't hang around any longer than they must. If the pool were to return the <em>least</em> recently used connection, it would be likely to result in a large pool of sparsely used connections because we'd keep resetting the last-used time of whichever connection is least recently used at that moment. </p>
</div><h2 class="groupheader">Constructor & Destructor Documentation</h2>
<a id="a2cee954229416e24da07f5e208b35b09"></a>
<h2 class="memtitle"><span class="permalink"><a href="#a2cee954229416e24da07f5e208b35b09">◆ </a></span>~ConnectionPool()</h2>
<div class="memitem">
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<table class="memname">
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<td class="memname">virtual mysqlpp::ConnectionPool::~ConnectionPool </td>
<td>(</td>
<td class="paramname"></td><td>)</td>
<td></td>
</tr>
</table>
</td>
<td class="mlabels-right">
<span class="mlabels"><span class="mlabel">inline</span><span class="mlabel">virtual</span></span> </td>
</tr>
</table>
</div><div class="memdoc">
<p>Destroy object. </p>
<p>If the pool raises an assertion on destruction, it means our subclass isn't calling <a class="el" href="classmysqlpp_1_1ConnectionPool.html#a981e1b1715de2daea9f6b10bdcbb5915" title="Drains the pool, freeing all allocated memory.">clear()</a> in its dtor as it should. </p>
</div>
</div>
<h2 class="groupheader">Member Function Documentation</h2>
<a id="a981e1b1715de2daea9f6b10bdcbb5915"></a>
<h2 class="memtitle"><span class="permalink"><a href="#a981e1b1715de2daea9f6b10bdcbb5915">◆ </a></span>clear()</h2>
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<td class="memname">void mysqlpp::ConnectionPool::clear </td>
<td>(</td>
<td class="paramtype">bool </td>
<td class="paramname"><em>all</em> = <code>true</code></td><td>)</td>
<td></td>
</tr>
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</td>
<td class="mlabels-right">
<span class="mlabels"><span class="mlabel">protected</span></span> </td>
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<p>Drains the pool, freeing all allocated memory. </p>
<p>A derived class must call this in its dtor to avoid leaking all <a class="el" href="classmysqlpp_1_1Connection.html" title="Manages the connection to the database server.">Connection</a> objects still in existence. We can't do it up at this level because this class's dtor can't call our subclass's <a class="el" href="classmysqlpp_1_1ConnectionPool.html#a3dae30e24dd6967e4e427fa69dbc2105" title="Destroy a connection.">destroy()</a> method.</p>
<dl class="params"><dt>Parameters</dt><dd>
<table class="params">
<tr><td class="paramname">all</td><td>if true, remove all connections, even those in use </td></tr>
</table>
</dd>
</dl>
<p class="reference">References <a class="el" href="classmysqlpp_1_1ConnectionPool.html#aae75febe979da2d4a3335c46438f3d33">remove()</a>.</p>
</div>
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<h2 class="memtitle"><span class="permalink"><a href="#af755c7e11b92bbab0e88ab3e9c88f0fd">◆ </a></span>create()</h2>
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<td class="memname">virtual <a class="el" href="classmysqlpp_1_1Connection.html">Connection</a>* mysqlpp::ConnectionPool::create </td>
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<p>Create a new connection. </p>
<p>Subclasses must override this.</p>
<p>Essentially, this method lets your code tell <a class="el" href="classmysqlpp_1_1ConnectionPool.html" title="Manages a pool of connections for programs that need more than one Connection object at a time,...">ConnectionPool</a> what server to connect to, what login parameters to use, what connection options to enable, etc. <a class="el" href="classmysqlpp_1_1ConnectionPool.html" title="Manages a pool of connections for programs that need more than one Connection object at a time,...">ConnectionPool</a> can't know any of this without your help.</p>
<dl class="retval"><dt>Return values</dt><dd>
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<tr><td class="paramname">A</td><td>connected <a class="el" href="classmysqlpp_1_1Connection.html" title="Manages the connection to the database server.">Connection</a> object </td></tr>
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<p class="reference">Referenced by <a class="el" href="classmysqlpp_1_1ConnectionPool.html#acbf56ee86ef66b3ebdf02adde5908776">grab()</a>.</p>
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<h2 class="memtitle"><span class="permalink"><a href="#a3dae30e24dd6967e4e427fa69dbc2105">◆ </a></span>destroy()</h2>
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<td class="memname">virtual void mysqlpp::ConnectionPool::destroy </td>
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<p>Destroy a connection. </p>
<p>Subclasses must override this.</p>
<p>This is for destroying the objects returned by <a class="el" href="classmysqlpp_1_1ConnectionPool.html#af755c7e11b92bbab0e88ab3e9c88f0fd" title="Create a new connection.">create()</a>. Because we can't know what the derived class did to create the connection we can't reliably know how to destroy it. </p>
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<h2 class="memtitle"><span class="permalink"><a href="#a4f9844f2c57c9f51f1b5a2b8a996ee15">◆ </a></span>exchange()</h2>
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<td class="memname"><a class="el" href="classmysqlpp_1_1Connection.html">Connection</a> * mysqlpp::ConnectionPool::exchange </td>
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<td class="paramtype">const <a class="el" href="classmysqlpp_1_1Connection.html">Connection</a> * </td>
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<p>Return a defective connection to the pool and get a new one back. </p>
<p>Call this on receiving a <a class="el" href="classmysqlpp_1_1BadQuery.html" title="Exception thrown when the database server encounters a problem while processing your query.">BadQuery</a> exception, with errnum() equal to CR_SERVER_GONE_ERROR. It means the server was restarted or otherwise dropped your connection to it, so the <a class="el" href="classmysqlpp_1_1Connection.html" title="Manages the connection to the database server.">Connection</a> object is no longer usable. You can avoid the need to use this by setting the <a class="el" href="classmysqlpp_1_1ReconnectOption.html" title="Enable automatic reconnection to server.">ReconnectOption</a> in your <a class="el" href="classmysqlpp_1_1ConnectionPool.html#acbf56ee86ef66b3ebdf02adde5908776" title="Grab a free connection from the pool.">grab()</a> override, but perhaps there are other reasons to need to exchange a bad connection for a good one.</p>
<p>This function wraps <a class="el" href="classmysqlpp_1_1ConnectionPool.html#acbf56ee86ef66b3ebdf02adde5908776" title="Grab a free connection from the pool.">grab()</a>, not <a class="el" href="classmysqlpp_1_1ConnectionPool.html#aac4d50bb5c603efec4b8d7e0a3e8a164" title="Grab a free connection from the pool, testing that it's connected before returning it.">safe_grab()</a>, even though that could return another dead connection. The assumption is that if your code is smart enough to detect one bad connection, it should be smart enough to detect a whole string of them. Worst case, the whole pool is bad – remote server went away – and we have to empty the pool and start re-filling it.</p>
<dl class="params"><dt>Parameters</dt><dd>
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<tr><td class="paramname">pc</td><td>pointer to a <a class="el" href="classmysqlpp_1_1Connection.html" title="Manages the connection to the database server.">Connection</a> object to be returned to the pool and marked as unused.</td></tr>
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<dl class="retval"><dt>Return values</dt><dd>
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<tr><td class="paramname">a</td><td>pointer to a different <a class="el" href="classmysqlpp_1_1Connection.html" title="Manages the connection to the database server.">Connection</a> object; not guaranteed to still be connected! </td></tr>
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<p class="reference">References <a class="el" href="classmysqlpp_1_1ConnectionPool.html#acbf56ee86ef66b3ebdf02adde5908776">grab()</a>, and <a class="el" href="classmysqlpp_1_1ConnectionPool.html#aae75febe979da2d4a3335c46438f3d33">remove()</a>.</p>
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<h2 class="memtitle"><span class="permalink"><a href="#acbf56ee86ef66b3ebdf02adde5908776">◆ </a></span>grab()</h2>
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<td class="memname"><a class="el" href="classmysqlpp_1_1Connection.html">Connection</a> * mysqlpp::ConnectionPool::grab </td>
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<p>Grab a free connection from the pool. </p>
<p>This method creates a new connection if an unused one doesn't exist, and destroys any that have remained unused for too long. If there is more than one free connection, we return the most recently used one; this allows older connections to die off over time when the caller's need for connections decreases.</p>
<p>Do not delete the returned pointer. This object manages the lifetime of connection objects it creates.</p>
<dl class="retval"><dt>Return values</dt><dd>
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<tr><td class="paramname">a</td><td>pointer to the connection </td></tr>
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<p class="reference">References <a class="el" href="classmysqlpp_1_1ConnectionPool.html#af755c7e11b92bbab0e88ab3e9c88f0fd">create()</a>.</p>
<p class="reference">Referenced by <a class="el" href="classmysqlpp_1_1ConnectionPool.html#a4f9844f2c57c9f51f1b5a2b8a996ee15">exchange()</a>, and <a class="el" href="classmysqlpp_1_1ConnectionPool.html#aac4d50bb5c603efec4b8d7e0a3e8a164">safe_grab()</a>.</p>
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<h2 class="memtitle"><span class="permalink"><a href="#a8a5ba414a5b02c48d64501c25b64a656">◆ </a></span>max_idle_time()</h2>
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<td class="memname">virtual unsigned int mysqlpp::ConnectionPool::max_idle_time </td>
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<p>Returns the maximum number of seconds a connection is able to remain idle before it is dropped. </p>
<p>Subclasses must override this as it encodes a policy issue, something that MySQL++ can't declare by fiat.</p>
<dl class="retval"><dt>Return values</dt><dd>
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<tr><td class="paramname">number</td><td>of seconds before an idle connection is destroyed due to lack of use </td></tr>
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<h2 class="memtitle"><span class="permalink"><a href="#ac51a7a63ce4d8825c3f7b05f4b8bfe68">◆ </a></span>release()</h2>
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<td class="memname">void mysqlpp::ConnectionPool::release </td>
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<td class="paramtype">const <a class="el" href="classmysqlpp_1_1Connection.html">Connection</a> * </td>
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<p>Return a connection to the pool. </p>
<p>Marks the connection as no longer in use.</p>
<p>The pool updates the last-used time of a connection only on release, on the assumption that it was used just prior. There's nothing forcing you to do it this way: your code is free to delay releasing idle connections as long as it likes. You want to avoid this because it will make the pool perform poorly; if it doesn't know approximately how long a connection has really been idle, it can't make good judgements about when to remove it from the pool.</p>
<dl class="params"><dt>Parameters</dt><dd>
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<tr><td class="paramname">pc</td><td>pointer to a <a class="el" href="classmysqlpp_1_1Connection.html" title="Manages the connection to the database server.">Connection</a> object to be returned to the pool and marked as unused. </td></tr>
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<p class="reference">Referenced by <a class="el" href="classmysqlpp_1_1ScopedConnection.html#ab8b21eb30678cb0530d6dbc1eed38bef">mysqlpp::ScopedConnection::~ScopedConnection()</a>.</p>
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<h2 class="memtitle"><span class="permalink"><a href="#aae75febe979da2d4a3335c46438f3d33">◆ </a></span>remove()</h2>
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<td class="memname">void mysqlpp::ConnectionPool::remove </td>
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<p>Removes the given connection from the pool. </p>
<p>If you mean to simply return a connection to the pool after you're finished using it, call <a class="el" href="classmysqlpp_1_1ConnectionPool.html#ac51a7a63ce4d8825c3f7b05f4b8bfe68" title="Return a connection to the pool.">release()</a> instead. This method is primarily for error handling: you somehow have figured out that the connection is defective, so want it destroyed and removed from the pool. If you also want a different connection to retry your operation on, call <a class="el" href="classmysqlpp_1_1ConnectionPool.html#a4f9844f2c57c9f51f1b5a2b8a996ee15" title="Return a defective connection to the pool and get a new one back.">exchange()</a> instead.</p>
<dl class="params"><dt>Parameters</dt><dd>
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<tr><td class="paramname">pc</td><td>pointer to a <a class="el" href="classmysqlpp_1_1Connection.html" title="Manages the connection to the database server.">Connection</a> object to be removed from the pool and destroyed </td></tr>
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<p class="reference">Referenced by <a class="el" href="classmysqlpp_1_1ConnectionPool.html#a981e1b1715de2daea9f6b10bdcbb5915">clear()</a>, <a class="el" href="classmysqlpp_1_1ConnectionPool.html#a4f9844f2c57c9f51f1b5a2b8a996ee15">exchange()</a>, and <a class="el" href="classmysqlpp_1_1ConnectionPool.html#aac4d50bb5c603efec4b8d7e0a3e8a164">safe_grab()</a>.</p>
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<h2 class="memtitle"><span class="permalink"><a href="#aac4d50bb5c603efec4b8d7e0a3e8a164">◆ </a></span>safe_grab()</h2>
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<td class="memname"><a class="el" href="classmysqlpp_1_1Connection.html">Connection</a> * mysqlpp::ConnectionPool::safe_grab </td>
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<p>Grab a free connection from the pool, testing that it's connected before returning it. </p>
<p>This is just a wrapper around <a class="el" href="classmysqlpp_1_1ConnectionPool.html#acbf56ee86ef66b3ebdf02adde5908776" title="Grab a free connection from the pool.">grab()</a>, <a class="el" href="classmysqlpp_1_1Connection.html#ac1dbc411f7ab1debbabe241561fe4091" title=""Pings" the database server">Connection::ping()</a> and <a class="el" href="classmysqlpp_1_1ConnectionPool.html#ac51a7a63ce4d8825c3f7b05f4b8bfe68" title="Return a connection to the pool.">release()</a>, and is thus less efficient than <a class="el" href="classmysqlpp_1_1ConnectionPool.html#acbf56ee86ef66b3ebdf02adde5908776" title="Grab a free connection from the pool.">grab()</a>. Use it only when it's possible for MySQL server connections to go away unexpectedly, such as when the DB server can be restarted out from under your application.</p>
<dl class="retval"><dt>Return values</dt><dd>
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<tr><td class="paramname">a</td><td>pointer to the connection </td></tr>
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<p class="reference">References <a class="el" href="classmysqlpp_1_1ConnectionPool.html#acbf56ee86ef66b3ebdf02adde5908776">grab()</a>, and <a class="el" href="classmysqlpp_1_1ConnectionPool.html#aae75febe979da2d4a3335c46438f3d33">remove()</a>.</p>
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<hr/>The documentation for this class was generated from the following files:<ul>
<li><a class="el" href="cpool_8h_source.html">cpool.h</a></li>
<li>cpool.cpp</li>
</ul>
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