314 lines
9.4 KiB
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314 lines
9.4 KiB
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<meta name="Copyright" content="Copyright (c) 2006 by IBM Corporation">
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<title>DosSetRelMaxFH()--Change Maximum Number of File Descriptors</title>
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<a name="Top_Of_Page"></a>
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<h2>DosSetRelMaxFH()--Change Maximum Number of File Descriptors</h2>
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<div class="box" style="width: 70%;">
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<br>
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Syntax<br>
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<pre>
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#define INCL_DOSERRORS
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#define INCL_DOSFILEMGR
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#include <os2.h>
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APIRET APIENTRY DosSetRelMaxFH(PLONG <em>pcbReqCount</em>,
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PULONG <em>pcbCurMaxFH</em>);
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</pre>
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Service Program Name: QP0LLIB1<br>
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<!-- iddvc RMBR -->
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<br>
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Default Public Authority: *USE<br>
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<br>
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Threadsafe: Yes<br>
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<!-- iddvc RMBR -->
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<br>
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</div>
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<p>The <strong>DosSetRelMaxFH()</strong> function requests that the system
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change the maximum number of file descriptors for the calling process (job).
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The system preserves all file descriptors that are currently open.</p>
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<p>A request to increase the maximum number of file descriptors by more than
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the system can accommodate will succeed. The resulting maximum will be the
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largest number possible, but will be less than what you requested.</p>
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<p>A request to decrease the maximum number of file descriptors will succeed.
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The resulting maximum will be the smallest number possible, but may be more
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than what you expected. For example, assume that the current maximum is 200 and
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there are 150 open files. A request to decrease the maximum by 75 results in
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the maximum being decreased by only 50, to 150, to preserve the open file
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descriptors.</p>
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<p>A request to decrease the maximum number of file descriptors to below 20
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will succeed, but the maximum will never be decreased below 20.</p>
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<p>To retrieve the current maximum number of file descriptors, without any side
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effects, the value pointed to by <em>pcbReqCount</em> should be set to
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zero.</p>
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<br>
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<h3>Parameters</h3>
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<dl>
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<dt><strong><em>pcbReqCount</em></strong></dt>
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<dd>(Input) A pointer to the number to be added to the maximum number of file
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descriptors for the calling process. If the value pointed to by <em>
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pcbReqCount</em> is positive, the system increases the maximum number of file
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descriptors. If the value pointed to by <em>pcbReqCount</em> is negative, the
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system decreases the maximum number of file descriptors.<br>
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</dd>
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<dt><strong><em>pcbCurMaxFH</em></strong></dt>
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<dd>(Output) A pointer to the location to receive the new total number of
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allocated file descriptors.</dd>
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</dl>
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<br>
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<h3>Authorities</h3>
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<p>No authorization is required.</p>
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<br>
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<h3>Return Value</h3>
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<dl compact>
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<dt><em>NO_ERROR (0)</em></dt>
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<dd><strong>DosSetRelMaxFH()</strong> was successful. The function returns <em>
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NO_ERROR (0)</em> even if the system disregards or partially fulfills a request
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for an increase or a decrease (for example, decreasing by a smaller number than
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requested). You should examine the value pointed to by <em>pcbCurMaxFH</em> to
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determine the result of this function.</dd>
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<dt><em>value (non-zero)</em></dt>
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<dd><strong>
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DosSetRelMaxFH()</strong> was not successful. The <em>value</em> that is
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returned indicates the error.</dd>
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</dl>
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<br>
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<h3>Error Conditions</h3>
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<p>If <strong>DosSetRelMaxFH()</strong> is not successful, the value that is
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returned is one of the following errors. The <<strong>bseerr.h</strong>>
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header file defines these values.</p>
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<dl compact>
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<dt><em>[ERROR_GEN_FAILURE]</em></dt>
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<dd>
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<p>A general failure occurred.</p>
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<p>This may result from damage in the system. Refer to messages in the job log
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for other possible causes.</p>
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<br>
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</dd>
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<dt><em>[ERROR_PROTECTION_VIOLATION]</em></dt>
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<dd>
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<p>A protection violation occurred.</p>
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<p>A pointer passed to this function is not a valid pointer.</p>
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</dd>
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</dl>
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<br>
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<h3>Error Messages</h3>
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<p>The system may send the following messages from this function.</p>
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<table width="100%" cellpadding="5">
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<!-- cols="15 85" -->
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<tr>
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<th align="left" valign="top">Message ID</th>
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<th align="left" valign="top">Error Message Text</th>
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</tr>
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<tr>
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<td width="15%" valign="top">CPE3418 E</td>
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<td width="85%" valign="top">Possible APAR condition or hardware failure.</td>
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</tr>
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<tr>
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<td valign="top">CPFA0D4 E</td>
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<td valign="top">File system error occurred. Error number &1.</td>
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</tr>
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<tr>
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<td valign="top">CPF3CF2 E</td>
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<td valign="top">Error(s) occurred during running of &1 API.</td>
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</tr>
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<tr>
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<td valign="top">CPF9872 E</td>
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<td valign="top">Program or service program &1 in library &2 ended.
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Reason code &3.</td>
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</tr>
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</table>
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<br>
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<br>
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<h3>Usage Notes</h3>
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<ol type="1">
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<li>If you are using the <a href="sselect.htm"><strong>select()</strong></a> API,
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you should be aware of
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the value of the FD_SETSIZE macro defined in the
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<<strong>sys/types.h</strong>> header file. This value is defined to be
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200. This means that the fd_set structure is defined to contain 200 bits, one
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for each file descriptor.
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<p>If your application uses <strong>DosSetRelMaxFH()</strong> to increase the
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maximum number of file descriptors beyond 200, you should consider defining
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your own value for the FD_SETSIZE macro prior to including
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<<strong>sys/types.h</strong>>. This is to ensure that the fd_set
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structure is defined with the correct number of bits to accommodate the actual
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maximum number of file descriptors.</p>
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</li>
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<li>The maximum number of file descriptors for this process may be obtained by
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using the <a href="sysconf.htm">sysconf()</a> API with the _SC_OPEN_MAX parameter.<br>
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<br>
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</li>
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<li>If this function is called
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by a thread executing one of the scan-related exit programs (or any of its
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created threads), it will fail with error code [ERROR_GEN_FAILURE]. See <a
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href="ifsopenexit.htm">Integrated File System Scan on Open Exit Programs</a>
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and <a href="ifscloseexit.htm">Integrated File System Scan on Close Exit
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Programs</a> for more information. </li>
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</ol>
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<br>
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<h3>Related Information</h3>
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<ul>
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<li>The <<strong>os2.h</strong>> file (see <a href="unix13.htm">Header
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Files for UNIX-Type Functions</a>)<br>
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</li>
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<li>The <<strong>os2def.h</strong>> file (see <a href="unix13.htm">Header
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Files for UNIX-Type Functions</a>)<br>
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</li>
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<li>The <<strong>bse.h</strong>> file (see <a href="unix13.htm">Header
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Files for UNIX-Type Functions</a>)<br>
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</li>
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<li>The <<strong>bsedos.h</strong>> file (see <a href="unix13.htm">Header
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Files for UNIX-Type Functions</a>)<br>
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</li>
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<li>The <<strong>bseerr.h</strong>> file (see <a href="unix13.htm">Header
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Files for UNIX-Type Functions</a>)<br>
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</li>
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<li>The <<strong>sys/types.h</strong>> file (see <a href="unix13.htm">
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Header Files for UNIX-Type Functions</a>)<br>
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</li>
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<li><a href="sselect.htm"><strong>select()</strong></a>--Wait for Events on Multiple Sockets<br>
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</li>
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<li><a href="sysconf.htm">sysconf()</a>--Get System Configuration
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Variables</li>
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</ul>
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<br>
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<h3>Example</h3>
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<p>See <a href="../apiref/aboutapis.htm#codedisclaimer">Code disclaimer information</a>
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for information pertaining to code examples.</p>
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<p>The following example increases the maximum number of file descriptors by
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two.</p>
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<pre>
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#define INCL_DOSERRORS
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#define INCL_DOSFILEMGR
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#include <os2.h>
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#include <stdio.h>
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void main()
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{
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long ReqCount = 0; /* Number to add to maximum */
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/* file descriptor count. */
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ulong CurMaxFH; /* New count of file descriptors. */
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int rc; /* Return code. */
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/* Find out what the initial maximum is.*/
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if ( NO_ERROR == (rc = DosSetRelMaxFH(&ReqCount, &CurMaxFH))
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{
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printf("Initial maximum = %d",CurMaxFH);
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ReqCount = 2; /* Set up to increase by 2. */
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if (NO_ERROR == (rc = DosSetRelMaxFH(&ReqCount, &CurMaxFH))
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{
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printf(" New maximum = %d",CurMaxFH);
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}
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}
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if (NO_ERROR != rc)
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{
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printf("Error = &d",rc);
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}
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}
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</pre>
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<p><strong>Output:</strong></p>
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<pre>
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Initial maximum = 200 New maximum = 202
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</pre>
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<hr>
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API introduced: V4R2
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<hr>
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<center>
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<table cellpadding="2" cellspacing="2">
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<tr align="center">
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<td valign="middle" align="center"><a href="#Top_Of_Page">Top</a> | <a href=
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"unix.htm">UNIX-Type APIs</a> | <a href="aplist.htm">APIs by category</a></td>
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</tr>
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</table>
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</center>
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</body>
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</html>
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