Manpage of PTHREAD_JOIN
PTHREAD_JOINSection: Linux Programmer's Manual (3)
NAMEpthread_join - join with a terminated thread
#include <pthread.h>int pthread_join(pthread_t thread, void **retval);
DESCRIPTIONThe pthread_join() function waits for the thread specified by threadto terminate. If that thread has already terminated, then pthread_join() returns immediately. The thread specified by threadmust be joinable.
If retvalis 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_CANCELEDis 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 VALUEOn success, pthread_join() returns 0; on error, it returns an error number.
- 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.
ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7).
CONFORMING TOPOSIX.1-2001, POSIX.1-2008.
NOTESAfter 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 hasly 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.
SEE ALSOpthread_cancel(3), pthread_create(3), pthread_detach(3), pthread_exit(3), pthread_tryjoin_np(3), pthreads(7)
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