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

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 unde-
       fined.   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).

       -Œ----------------¬----------------¬----------
       -‚Interface      -‚ Attribute     -‚ Value   -‚
       "----------------¼----------------¼----------¤
       -‚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 ter-
       mination 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/.

Linux                                       2017-09-15                            PTHREAD_JOIN(3)