forking in multithreaded program

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pthread_join

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 loca-
       tion 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 function-
       ality, 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)

UNIX for Advanced & Expert Users