pthread_join - join with a terminated thread
#include <pthread.h>
int pthread_join(pthread_t thread, void **retval);
Compile and link with
-pthread.
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 undefined. If the thread calling
pthread_join() is canceled, then
the target thread will remain joinable (i.e., it will not be detached).
On success,
pthread_join() returns 0; on error, it returns an error
number.
- 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.
For an explanation of the terms used in this section, see
attributes(7).
Interface |
Attribute |
Value |
pthread_join () |
Thread safety |
MT-Safe |
POSIX.1-2001, POSIX.1-2008.
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.
See
pthread_create(3).
pthread_cancel(3),
pthread_create(3),
pthread_detach(3),
pthread_exit(3),
pthread_tryjoin_np(3),
pthreads(7)