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

       pthread_join - join with a terminated thread

       #include <pthread.h>

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

       Compile and link with -pthread.

       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

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

              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.

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

       │Interface                                     Attribute     Value   │
       │pthread_join()                                │ Thread safety │ MT-Safe │

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

       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.

       See pthread_create(3).

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

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       latest version of this page, can be found at

Linux                              2021-03-22                    PTHREAD_JOIN(3)