216 lines
7.8 KiB
HTML
216 lines
7.8 KiB
HTML
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<title>pthread_join</title>
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<basefont size="3"> <a name="pthread_join"></a> <a name="tag_03_533"></a><!-- pthread_join -->
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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_533_01"></a>NAME</h4>
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<blockquote>pthread_join - wait for thread termination</blockquote>
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<h4><a name="tag_03_533_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_join(pthread_t</tt> <i>thread</i><tt>, void **</tt><i>value_ptr</i><tt>); <img src="../images/opt-end.gif" alt=
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"[Option End]" border="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_533_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>pthread_join</i>() function shall suspend execution of the calling thread until the target <i>thread</i> terminates,
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unless the target <i>thread</i> has already terminated. On return from a successful <i>pthread_join</i>() call with a non-NULL
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<i>value_ptr</i> argument, the value passed to <a href="../functions/pthread_exit.html"><i>pthread_exit</i>()</a> by the
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terminating thread shall be made available in the location referenced by <i>value_ptr</i>. When a <i>pthread_join</i>() returns
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successfully, the target thread has been terminated. The results of multiple simultaneous calls to <i>pthread_join</i>() specifying
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the same target thread are undefined. If the thread calling <i>pthread_join</i>() is canceled, then the target thread shall not be
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detached.</p>
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<p>It is unspecified whether a thread that has exited but remains unjoined counts against {PTHREAD_THREADS_MAX}.</p>
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</blockquote>
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<h4><a name="tag_03_533_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>If successful, the <i>pthread_join</i>() function shall return zero; otherwise, an error number shall be returned to indicate
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the error.</p>
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</blockquote>
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<h4><a name="tag_03_533_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>pthread_join</i>() function shall fail if:</p>
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<dl compact>
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<dt>[EINVAL]</dt>
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<dd>The implementation has detected that the value specified by <i>thread</i> does not refer to a joinable thread.</dd>
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<dt>[ESRCH]</dt>
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<dd>No thread could be found corresponding to that specified by the given thread ID.</dd>
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</dl>
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<p>The <i>pthread_join</i>() function may fail if:</p>
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<dl compact>
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<dt>[EDEADLK]</dt>
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<dd>A deadlock was detected or the value of <i>thread</i> specifies the calling thread.</dd>
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</dl>
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<p>The <i>pthread_join</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_533_06"></a>EXAMPLES</h4>
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<blockquote>
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<p>An example of thread creation and deletion follows:</p>
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<pre>
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<tt>typedef struct {
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int *ar;
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long n;
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} subarray;
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<br>
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void *
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incer(void *arg)
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{
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long i;
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<br>
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for (i = 0; i < ((subarray *)arg)->n; i++)
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((subarray *)arg)->ar[i]++;
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}
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<br>
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int main(void)
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{
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int ar[1000000];
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pthread_t th1, th2;
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subarray sb1, sb2;
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<br>
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sb1.ar = &ar[0];
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sb1.n = 500000;
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(void) pthread_create(&th1, NULL, incer, &sb1);
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<br>
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sb2.ar = &ar[500000];
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sb2.n = 500000;
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(void) pthread_create(&th2, NULL, incer, &sb2);
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<br>
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(void) pthread_join(th1, NULL);
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(void) pthread_join(th2, NULL);
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return 0;
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}
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</tt>
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</pre>
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</blockquote>
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<h4><a name="tag_03_533_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_533_08"></a>RATIONALE</h4>
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<blockquote>
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<p>The <i>pthread_join</i>() function is a convenience that has proven useful in multi-threaded applications. It is true that a
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programmer could simulate this function if it were not provided by passing extra state as part of the argument to the
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<i>start_routine</i>(). The terminating thread would set a flag to indicate termination and broadcast a condition that is part of
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that state; a joining thread would wait on that condition variable. While such a technique would allow a thread to wait on more
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complex conditions (for example, waiting for multiple threads to terminate), waiting on individual thread termination is considered
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widely useful. Also, including the <i>pthread_join</i>() function in no way precludes a programmer from coding such complex waits.
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Thus, while not a primitive, including <i>pthread_join</i>() in this volume of IEEE Std 1003.1-2001 was considered
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valuable.</p>
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<p>The <i>pthread_join</i>() function provides a simple mechanism allowing an application to wait for a thread to terminate. After
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the thread terminates, the application may then choose to clean up resources that were used by the thread. For instance, after
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<i>pthread_join</i>() returns, any application-provided stack storage could be reclaimed.</p>
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<p>The <i>pthread_join</i>() or <a href="../functions/pthread_detach.html"><i>pthread_detach</i>()</a> function should eventually
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be called for every thread that is created with the <i>detachstate</i> attribute set to PTHREAD_CREATE_JOINABLE so that storage
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associated with the thread may be reclaimed.</p>
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<p>The interaction between <i>pthread_join</i>() and cancelation is well-defined for the following reasons:</p>
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<ul>
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<li>
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<p>The <i>pthread_join</i>() function, like all other non-async-cancel-safe functions, can only be called with deferred
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cancelability type.</p>
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</li>
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<li>
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<p>Cancelation cannot occur in the disabled cancelability state.</p>
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</li>
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</ul>
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<p>Thus, only the default cancelability state need be considered. As specified, either the <i>pthread_join</i>() call is canceled,
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or it succeeds, but not both. The difference is obvious to the application, since either a cancelation handler is run or
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<i>pthread_join</i>() returns. There are no race conditions since <i>pthread_join</i>() was called in the deferred cancelability
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state.</p>
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</blockquote>
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<h4><a name="tag_03_533_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_533_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="pthread_create.html"><i>pthread_create</i>()</a> , <a href="wait.html"><i>wait</i>()</a> , the Base Definitions volume
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of IEEE Std 1003.1-2001, <a 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_533_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 5. Included for alignment with the POSIX Threads Extension.</p>
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</blockquote>
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<h4><a name="tag_03_533_12"></a>Issue 6</h4>
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<blockquote>
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<p>The <i>pthread_join</i>() function is marked as part of the Threads option.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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<hr>
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<center><font size="2"><!--footer start-->
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UNIX ® is a registered Trademark of The Open Group.<br>
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POSIX ® is a registered Trademark of The IEEE.<br>
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