PTHREAD_JOIN(3P)					     POSIX Programmer's Manual						  PTHREAD_JOIN(3P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing 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 referenced 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 target 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; otherwise, 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 sim-
       ulate  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  condi-
       tion  variable.	 While such a technique would allow a thread to wait on more complex conditions (for example, waiting for multiple threads
       to terminate), 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  primitive, 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 specified, 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 cancelability 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 Technol-
       ogy -- 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(3P)