Section (3) pthread_join
pthread_join — join with a terminated thread
Compile and link with
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.
retval is not
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
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).
A deadlock was detected (e.g., two threads tried to join with each other); or
threadspecifies the calling thread.
threadis not a joinable thread.
Another thread is already waiting to join with this thread.
No thread with the ID
threadcould be found.
For an explanation of the terms used in this section, see attributes(7).
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.
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Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk
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