301 lines
8.2 KiB
HTML
301 lines
8.2 KiB
HTML
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<meta name="Copyright" content="Copyright (c) 2006 by IBM Corporation">
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<title>sem_init_np()-Initialize Unnamed Semaphore with Maximum Value</title>
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<a name="Top_Of_Page"></a>
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<h2>sem_init_np()--Initialize Unnamed Semaphore with Maximum Value</h2>
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<div class="box" style="width: 60%;">
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<br>
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Syntax<br>
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<pre>
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#include <semaphore.h>
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int sem_init_np(sem_t * <em>sem</em>, int <em>shared</em>,
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unsigned int <em>value</em>,
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sem_attr_np_t * <em>attr</em>);
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</pre>
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<br>
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Service Program Name: QP0ZPSEM<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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<!-- iddvc RMBR -->
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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>sem_init_np()</strong> function initializes an unnamed semaphore
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and sets its initial value. The <strong>sem_init_np()</strong> function uses
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the <em>attr</em> parameter to set the maximum value and title of the
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semaphore. If an unnamed semaphore already exists at <em>sem</em>, then it
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will be destroyed and a new semaphore will be initialized.</p>
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<br>
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<h3>Parameters</h3>
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<dl>
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<dt><strong>sem</strong></dt>
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<dd>(Input) A pointer to the storage of an uninitialized unnamed semaphore. The
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pointer must be aligned on a 16-byte boundary. This semaphore is
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initialized.<br>
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<br>
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</dd>
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<dt><strong>shared</strong></dt>
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<dd>(Input) An indication to the system of how the semaphore is going to be
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used. A value of zero indicates that the semaphore will be used only by threads
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within the current process. A nonzero value indicates that the semaphore may be
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used by threads from other processes.<br>
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<br>
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</dd>
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<dt><strong>value</strong></dt>
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<dd>(Input) The value used to initialize the value of the semaphore.<br>
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<br>
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</dd>
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<dt><strong>attr</strong></dt>
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<dd>(Input) Attributes for the semaphore.
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<p>The members of the sem_attr_np_t structure are as follows.</p>
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<table cellpadding="5">
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<!-- cols="15 85" -->
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<tr>
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<td align="left" valign="top" nowrap><em>unsigned int reserved1[1]</em></td>
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<td align="left" valign="top">A reserved field that must be set to zero.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>unsigned int maxvalue</em></td>
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<td align="left" valign="top">The maximum value that the semaphore may obtain.
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<em>maxvalue</em> must be greater than zero. If a <strong>sem_post()</strong>
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or <strong>sem_post_np()</strong> operation would cause the value of a
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semaphore to exceed its maximum value, the operation will fail, returning
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EINVAL.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>unsigned int reserved2[2]</em></td>
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<td align="left" valign="top">A reserved field that must be set to zero.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>char title[16]</em></td>
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<td align="left" valign="top">The title of the semaphore. The title is a
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null-terminated string that contains up to 16 bytes. Any bytes after the null
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character are ignored. The title is retrieved using the Open List of
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Interprocess Communication Objects (QP0ZOLIP) API.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>void * reserved3[2]</em></td>
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<td align="left" valign="top">A reserved field that must be set to zero.</td>
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</tr>
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</table>
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</dd>
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</dl>
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<br>
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<h3>Authorities</h3>
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<p>None</p>
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<br>
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<h3>Return Value</h3>
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<table cellpadding="5">
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<!-- cols="5 95" -->
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<tr>
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<td align="left" valign="top"><em>0</em></td>
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<td align="left" valign="top"><strong>sem_init_np()</strong> was
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successful.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>-1</em></td>
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<td align="left" valign="top"><strong>sem_init_np()</strong> was not
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successful. The <em>errno</em> variable is set to indicate the error.</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>Error Conditions</h3>
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<p>If <strong>sem_init_np()</strong> is not successful, <em>errno</em>
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usually indicates one of the following errors. Under some conditions, <em>
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errno</em> could indicate an error other than those listed here.</p>
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<dl>
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<dt><em>[EINVAL]</em></dt>
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<dd>
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<p>The value specified for the argument is not correct.</p>
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<p>A function was passed incorrect argument values, or an operation was
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attempted on an object and the operation specified is not supported for that
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type of object.</p>
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<p>An argument value is not valid, out of range, or NULL.</p>
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<p>The <em>value</em> parameter is greater than the <samp>maxvalue</samp>
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field of the <em>attr</em> parameter.</p>
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<p>The <samp>maxvalue</samp> field of the <em>attr</em> parameter is greater
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than SEM_VALUE_MAX.</p>
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<p>The <samp>maxvalue</samp> field of the <em>attr</em> parameter is equal to
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zero.</p>
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<p>The reserved fields of the <em>attr</em> argument are not set to zero.</p>
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</dd>
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<dt><em>[EFAULT]</em></dt>
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<dd>
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<p>The address used for an argument is not correct.</p>
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<p>In attempting to use an argument in a call, the system detected an address
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that is not valid.</p>
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<p>While attempting to access a parameter passed to this function, the system
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detected an address that is not valid.</p>
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</dd>
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<dt><em>[ENOSPC]</em></dt>
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<dd>
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<p>No space available.</p>
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<p>The requested operations required additional space on the device and there
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is no space left. This could also be caused by exceeding the user profile
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storage limit when creating or transferring ownership of an object.</p>
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<p>Insufficient space remains to hold the intended file, directory, or
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link.</p>
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<p>System semaphore resources have been exhausted.</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>None.</p>
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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>semaphore.h</strong>> file (see <a href="unix13.htm">
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Header Files for UNIX-Type Functions</a>)<br>
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<br>
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</li>
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<li><a href="ipcsemde.htm">sem_destroy()</a>--Destroy Unnamed Semaphore<br>
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<br>
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</li>
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<li><a href="ipcsemge.htm">sem_getvalue()</a>--Get Semaphore Value<br>
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<br>
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</li>
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<li><a href="ipcsemi.htm">sem_init()</a>--Initialize Unnamed Semaphore<br>
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<br>
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</li>
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<li><a href="ipcsemp.htm">sem_post()</a>--Post to Semaphore<br>
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<br>
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</li>
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<li><a href="ipcsempn.htm">sem_post_np()</a>--Post Value to Semaphore<br>
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<br>
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</li>
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<li><a href="ipcsemtr.htm">sem_trywait()</a>--Try to Decrement Semaphore<br>
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<br>
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</li>
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<li><a href="ipcsemw.htm">sem_wait()</a>--Wait for Semaphore<br>
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<br>
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</li>
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<li><a href="ipcsemwn.htm">sem_wait_np()</a>--Wait for Semaphore with
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Timeout</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 initializes an unnamed semaphore, my_semaphore, that
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will be used by threads of the current process and sets its value to 10. The
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maximum value and title of the semaphore are set to 10 and "MYSEM".</p>
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<pre>
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#include <semaphore.h>
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main() {
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sem_t my_semaphore;
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sem_attr_np_t attr;
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int rc;
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memset(&attr, 0, sizeof(attr));
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attr.maxvalue = 10;
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strcpy(attr.title, "MYSEM");
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rc = sem_init_np(&my_semaphore, 0, 10, &attr);
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}
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</pre>
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<br>
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<hr>
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API introduced: V4R4
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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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