180 lines
6.4 KiB
HTML
180 lines
6.4 KiB
HTML
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<title>pthread_rwlock_unlock</title>
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<basefont size="3"> <a name="pthread_rwlock_unlock"></a> <a name="tag_03_561"></a><!-- pthread_rwlock_unlock -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_561_01"></a>NAME</h4>
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<blockquote>pthread_rwlock_unlock - unlock a read-write lock object</blockquote>
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<h4><a name="tag_03_561_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('THR')">THR</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> #include <<a href="../basedefs/pthread.h.html">pthread.h</a>><br>
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<br>
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int pthread_rwlock_unlock(pthread_rwlock_t</tt> <i>*rwlock</i><tt>); <img src="../images/opt-end.gif" alt="[Option End]" border=
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"0"></tt></code></div>
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<tt><br>
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</tt></blockquote>
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<h4><a name="tag_03_561_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>pthread_rwlock_unlock</i>() function shall release a lock held on the read-write lock object referenced by <i>rwlock</i>.
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Results are undefined if the read-write lock <i>rwlock</i> is not held by the calling thread.</p>
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<p>If this function is called to release a read lock from the read-write lock object and there are other read locks currently held
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on this read-write lock object, the read-write lock object remains in the read locked state. If this function releases the last
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read lock for this read-write lock object, the read-write lock object shall be put in the unlocked state with no owners.</p>
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<p>If this function is called to release a write lock for this read-write lock object, the read-write lock object shall be put in
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the unlocked state.</p>
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<p>If there are threads blocked on the lock when it becomes available, the scheduling policy shall determine which thread(s) shall
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acquire the lock. <sup>[<a href="javascript:open_code('TPS')">TPS</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> If the Thread Execution Scheduling option is supported, when threads executing with the
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scheduling policies SCHED_FIFO, SCHED_RR, or SCHED_SPORADIC are waiting on the lock, they shall acquire the lock in priority order
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when the lock becomes available. For equal priority threads, write locks shall take precedence over read locks. <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"> If the Thread Execution Scheduling option is not supported, it is
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implementation-defined whether write locks take precedence over read locks.</p>
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<p>Results are undefined if any of these functions are called with an uninitialized read-write lock.</p>
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</blockquote>
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<h4><a name="tag_03_561_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>If successful, the <i>pthread_rwlock_unlock</i>() function shall return zero; otherwise, an error number shall be returned to
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indicate the error.</p>
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</blockquote>
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<h4><a name="tag_03_561_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>pthread_rwlock_unlock</i>() function may fail if:</p>
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<dl compact>
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<dt>[EINVAL]</dt>
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<dd>The value specified by <i>rwlock</i> does not refer to an initialized read-write lock object.</dd>
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<dt>[EPERM]</dt>
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<dd>The current thread does not hold a lock on the read-write lock.</dd>
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</dl>
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<p>The <i>pthread_rwlock_unlock</i>() function shall not return an error code of [EINTR].</p>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_561_06"></a>EXAMPLES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_561_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_561_08"></a>RATIONALE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_561_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_561_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="pthread_rwlock_destroy.html"><i>pthread_rwlock_destroy</i>()</a> , <a href=
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"pthread_rwlock_rdlock.html"><i>pthread_rwlock_rdlock</i>()</a> , <a href=
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"pthread_rwlock_timedrdlock.html"><i>pthread_rwlock_timedrdlock</i>()</a> , <a href=
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"pthread_rwlock_timedwrlock.html"><i>pthread_rwlock_timedwrlock</i>()</a> , <a href=
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"pthread_rwlock_tryrdlock.html"><i>pthread_rwlock_tryrdlock</i>()</a> , <a href=
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"pthread_rwlock_trywrlock.html"><i>pthread_rwlock_trywrlock</i>()</a> , <a href=
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"pthread_rwlock_wrlock.html"><i>pthread_rwlock_wrlock</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a
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href="../basedefs/pthread.h.html"><i><pthread.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_561_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 5.</p>
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</blockquote>
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<h4><a name="tag_03_561_12"></a>Issue 6</h4>
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<blockquote>
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<p>The following changes are made for alignment with IEEE Std 1003.1j-2000:</p>
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<ul>
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<li>
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<p>The margin code in the SYNOPSIS is changed to THR to indicate that the functionality is now part of the Threads option
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(previously it was part of the Read-Write Locks option in IEEE Std 1003.1j-2000 and also part of the XSI extension).</p>
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</li>
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<li>
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<p>The DESCRIPTION is updated as follows:</p>
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<ul>
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<li>
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<p>The conditions under which writers have precedence over readers are specified.</p>
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</li>
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<li>
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<p>The concept of read-write lock owner is deleted.</p>
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</li>
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</ul>
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</li>
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<li>
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<p>The SEE ALSO section is updated.</p>
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</li>
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</ul>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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