Multithreaded Programming Guide

Wait for Thread Termination


Use pthread_join(3THR) to wait for a thread to terminate.

int	pthread_join(thread_t tid, void **status);
#include <pthread.h>

pthread_t tid;
int ret;
void *status;

/* waiting to join thread "tid" with status */
ret = pthread_join(tid, &status);

/* waiting to join thread "tid" without status */
ret = pthread_join(tid, NULL); 

The pthread_join() function blocks the calling thread until the specified thread terminates.

The specified thread must be in the current process and must not be detached. For information on thread detachment, see Set Detach State.

When status is not NULL, it points to a location that is set to the exit status of the terminated thread when pthread_join() returns successfully.

If multiple threads wait for the same thread to terminate, they all wait until the target thread terminates, than one thread returns successfully and the others fail with an error of ESRCH.

After pthread_join() returns, any data storage associated with the thread can be reclaimed by the application.

Return Values

pthread_join() returns zero when it completes successfully. Any other return value indicates that an error occurred. When any of the following conditions are detected, pthread_join() fails and returns the corresponding value.


tid is not a valid, undetached thread in the current process.


A deadlock would exist, such as a thread waits for itself or thread A waits for thread B and thread B waits for thread A.


The value of tid is invalid.

Remember that pthread_join() works only for target threads that are nondetached. When there is no reason to synchronize with the termination of a particular thread, then that thread should be detached.