pthread_join(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLES | SEE ALSO | COLOPHON

PTHREAD_JOIN(3)         Linux Programmer's Manual        PTHREAD_JOIN(3)

NAME         top

       pthread_join - join with a terminated thread

SYNOPSIS         top

       #include <pthread.h>

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

       Compile and link with -pthread.

DESCRIPTION         top

       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 the location pointed to by 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         top

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

ERRORS         top

       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         top

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

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

CONFORMING TO         top

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

NOTES         top

       After a successful call to pthread_join(), the caller is
       guaranteed that the target thread has terminated.  The caller may
       then choose to do any clean-up that is required after termination
       of the thread (e.g., freeing memory or other resources that were
       allocated to the target thread).

       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.

EXAMPLES         top

       See pthread_create(3).

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.11 of the Linux man-pages project.
       A description of the project, information about reporting bugs,
       and the latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

Linux                          2021-03-22                PTHREAD_JOIN(3)

Pages that refer to this page: pthread_attr_setdetachstate(3)pthread_cancel(3)pthread_create(3)pthread_detach(3)pthread_exit(3)pthread_tryjoin_np(3)