C language pthread_ Join() function

man 1 pthread_join

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

NAME
       pthread_join - join with a terminated thread	// Connect to 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.
       //pthread_join()  Function waits for the thread specified by the thread to terminate . 
       // If the thread has terminated , be  pthread_join()  Return immediately . 
       //thread  The specified thread must be connectable .

       If retval is not NULL, then pthread_join() copies the exit status of the target thread (i.e., the value that the target  thread  sup‐plied  to  pthread_exit(3))  into  the  location  pointed to by *retval.  If the target thread was canceled, then PTHREAD_CANCELED is placed in *retval.
       // If  retval  Not for  NULL, be  pthread_join()  The exit state of the target thread （ That is, the target thread is provided to  pthread_exit(3)  Value ） Copied to the  *retval  Point to . 
       // If the target thread is cancelled , be  PTHREAD_CANCELED  Be placed in  *retval  in .

       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).
       // If multiple threads try to connect with the same thread at the same time , The result is undefined . 
       // If the  pthread_join()  The thread of was canceled , Then the target thread will remain available join() state （ That is, it won't detached()）.

RETURN VALUE
       On success, pthread_join() returns 0; on error, it returns an error number.
       // success ,pthread_join()  return  0;  When something goes wrong , 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.
       // On successful call  pthread_join()  after , The caller can guarantee that the target thread has terminated .

       Joining with a thread that has previously been joined results in undefined behavior.
       //join() Previously join() Threads of lead to 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).
       // Failed to connect with （joinable） The thread of （ That is, the threads that are not separated ） The connection will produce “ Zombie Threads ”.  Avoid doing this , Because each zombie thread will consume some system resources , When enough zombie threads are accumulated , You will no longer be able to create new threads （ Or the process ）.

       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.
       // No similar to  waitpid(-1, &status, 0)  Of  pthreads, namely “join Any terminated thread ”. 
       // If you think you need this function , You may 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.
       // All threads in the process are equal ： Any thread can interact with any other thread in the process join.

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 4.04 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 http://www.kernel.org/doc/man-pages/.

Linux                                                            2015-07-23                                                  PTHREAD_JOIN(3)
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