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 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 │
       └───────────────┴───────────────┴─────────┘

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.  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.

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

       This  page  is  part of release 4.15 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/.