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PTHREAD_JOIN(P)		   POSIX Programmer's Manual	       PTHREAD_JOIN(P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the	 corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.

NAME
       pthread_join - wait for thread termination

SYNOPSIS
       #include <pthread.h>

       int pthread_join(pthread_t thread, void **value_ptr);


DESCRIPTION
       The pthread_join() function shall  suspend  execution  of  the  calling
       thread until the target thread terminates, unless the target thread has
       already terminated. On return from  a  successful  pthread_join()  call
       with  a non-NULL value_ptr argument, the value passed to pthread_exit()
       by the terminating thread shall be made available in the location  ref-
       erenced	by  value_ptr. When a pthread_join() returns successfully, the
       target thread has been terminated. The results of multiple simultaneous
       calls  to  pthread_join()  specifying  the same target thread are unde-
       fined. If the thread calling pthread_join() is canceled, then the  tar-
       get thread shall not be detached.

       It is unspecified whether a thread that has exited but remains unjoined
       counts against {PTHREAD_THREADS_MAX}.

RETURN VALUE
       If successful, the pthread_join() function shall	 return	 zero;	other-
       wise, an error number shall be returned to indicate the error.

ERRORS
       The pthread_join() function shall fail if:

       EINVAL The  implementation  has	detected  that	the value specified by
	      thread does not refer to a joinable thread.

       ESRCH  No thread could be found corresponding to that specified by  the
	      given thread ID.


       The pthread_join() function may fail if:

       EDEADLK
	      A	 deadlock  was	detected  or the value of thread specifies the
	      calling thread.


       The pthread_join() function shall not return an error code of  [EINTR].

       The following sections are informative.

EXAMPLES
       An example of thread creation and deletion follows:


	      typedef struct {
		  int *ar;
		  long n;
	      } subarray;


	      void *
	      incer(void *arg)
	      {
		  long i;


		  for (i = 0; i < ((subarray *)arg)->n; i++)
		      ((subarray *)arg)->ar[i]++;
	      }


	      int main(void)
	      {
		  int	     ar[1000000];
		  pthread_t  th1, th2;
		  subarray   sb1, sb2;


		  sb1.ar = &ar[0];
		  sb1.n	 = 500000;
		  (void) pthread_create(&th1, NULL, incer, &sb1);


		  sb2.ar = &ar[500000];
		  sb2.n	 = 500000;
		  (void) pthread_create(&th2, NULL, incer, &sb2);


		  (void) pthread_join(th1, NULL);
		  (void) pthread_join(th2, NULL);
		  return 0;
	      }

APPLICATION USAGE
       None.

RATIONALE
       The  pthread_join() function is a convenience that has proven useful in
       multi-threaded applications. It is true that a programmer  could	 simu-
       late  this  function  if it were not provided by passing extra state as
       part of the argument to the  start_routine().  The  terminating	thread
       would set a flag to indicate termination and broadcast a condition that
       is part of that state; a joining thread would wait  on  that  condition
       variable.   While such a technique would allow a thread to wait on more
       complex conditions (for example, waiting for multiple threads to termi-
       nate),  waiting	on  individual thread termination is considered widely
       useful. Also, including the pthread_join() function in no way precludes
       a  programmer from coding such complex waits.  Thus, while not a primi-
       tive, including pthread_join() in this volume  of  IEEE Std 1003.1-2001
       was considered valuable.

       The  pthread_join()  function  provides	a simple mechanism allowing an
       application to wait for a thread to terminate. After the thread	termi-
       nates,  the application may then choose to clean up resources that were
       used by the thread. For instance,  after	 pthread_join()	 returns,  any
       application-provided stack storage could be reclaimed.

       The  pthread_join()  or	pthread_detach() function should eventually be
       called for every thread that is created with the detachstate  attribute
       set  to	PTHREAD_CREATE_JOINABLE	 so  that  storage associated with the
       thread may be reclaimed.

       The interaction between pthread_join() and cancellation is well-defined
       for the following reasons:

	* The  pthread_join()  function,  like all other non-async-cancel-safe
	  functions, can only be called with deferred cancelability type.


	* Cancellation cannot occur in the disabled cancelability state.


       Thus, only the default cancelability state need be considered. As spec-
       ified,  either the pthread_join() call is canceled, or it succeeds, but
       not both. The difference is obvious to the application, since either  a
       cancellation  handler  is  run  or pthread_join() returns. There are no
       race conditions since pthread_join() was called in the deferred	cance-
       lability state.

FUTURE DIRECTIONS
       None.

SEE ALSO
       pthread_create()	  ,   wait()   ,   the	 Base  Definitions  volume  of
       IEEE Std 1003.1-2001, <pthread.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),	The  Open  Group  Base
       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the
       event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard
       is  the	referee document. The original Standard can be obtained online
       at http://www.opengroup.org/unix/online.html .



IEEE/The Open Group		     2003		       PTHREAD_JOIN(P)
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