pthread_join(3)            Library Functions Manual            pthread_join(3)

NAME
       pthread_join - join with a terminated thread

LIBRARY
       POSIX threads library (libpthread, -lpthread)

SYNOPSIS
       #include <pthread.h>

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

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 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
       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 |
       +--------------------------------------------+---------------+---------+
STANDARDS
       POSIX.1-2008.

HISTORY
       POSIX.1-2001.

NOTES
       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
       See pthread_create(3).

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

Linux man-pages 6.7               2023-10-31                   pthread_join(3)