NAME

       pthread_join - join with a terminated thread

SYNOPSIS

       #include <pthread.h>

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

       Compile and link with -pthread.

DESCRIPTION

       The  pthread_join()  function  waits for the thread specified by thread to terminate.  If that thread has
       already terminated, then pthread_join() returns immediately.  The thread  specified  by  thread  must  be
       joinable.

       If  retval  is not NULL, then pthread_join() copies the exit status of the target thread (i.e., the value
       that the target thread supplied to pthread_exit(3)) into the location pointed  to  by  *retval.   If  the
       target thread was canceled, then PTHREAD_CANCELED is placed in *retval.

       If  multiple  threads simultaneously try to join with the same thread, the results are undefined.  If the
       thread calling pthread_join() is canceled, then the target thread will remain joinable (i.e., it will not
       be detached).

RETURN VALUE

       On success, pthread_join() returns 0; on error, it returns an error number.

ERRORS

       EDEADLK
              A deadlock was detected (e.g., two threads tried to join with each other); or thread specifies the
              calling thread.

       EINVAL thread is not a joinable thread.

       EINVAL Another thread is already waiting to join with this thread.

       ESRCH  No thread with the ID thread could be found.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌───────────────┬───────────────┬─────────┐
       │Interface      │ Attribute     │ Value   │
       ├───────────────┼───────────────┼─────────┤
       │pthread_join() │ Thread safety │ MT-Safe │
       └───────────────┴───────────────┴─────────┘

CONFORMING TO

       POSIX.1-2001, POSIX.1-2008.

NOTES

       After a successful call  to  pthread_join(),  the  caller  is  guaranteed  that  the  target  thread  has
       terminated.

       Joining with a thread that has previously been joined results in undefined behavior.

       Failure  to  join  with  a  thread  that is joinable (i.e., one that is not detached), produces a "zombie
       thread".  Avoid doing this, since each zombie thread consumes some  system  resources,  and  when  enough
       zombie threads have accumulated, it will no longer be possible to create new threads (or processes).

       There  is  no pthreads analog of waitpid(-1, &status, 0), that is, "join with any terminated thread".  If
       you believe you need this functionality, you probably need to rethink your application design.

       All of the threads in a process are peers: any thread can join with any other thread in the process.

EXAMPLE

       See pthread_create(3).

SEE ALSO

       pthread_cancel(3),   pthread_create(3),   pthread_detach(3),   pthread_exit(3),    pthread_tryjoin_np(3),
       pthreads(7)

COLOPHON

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