NAME

pthread_join, pthread_peekjoin_np, pthread_timedjoin_np — inspect thread termination state

LIBRARY

POSIX Threads Library (libpthread, -lpthread)

SYNOPSIS

#include <pthread.h>

int
pthread_join(pthread_t thread, void **value_ptr);

#include <pthread_np.h>

int
pthread_peekjoin_np(pthread_t thread, void **value_ptr);

int
pthread_timedjoin_np(pthread_t thread, void **value_ptr, const struct timespec *abstime);

DESCRIPTION

The pthread_join() function suspends execution of the calling thread until the target thread terminates unless the target thread has already terminated.

On return from a successful pthread_join() call with a non-NULL value_ptr argument, the value passed to pthread_exit() by the terminating thread is stored in the location referenced by value_ptr. When a pthread_join() returns successfully, the target thread has been terminated. The results of multiple simultaneous calls to pthread_join() specifying the same target thread are undefined. If the thread calling pthread_join() is cancelled, then the target thread is not detached.

The pthread_timedjoin_np() function is equivalent to the pthread_join() function except it will return ETIMEDOUT if target thread does not exit before specified absolute time passes.

The pthread_peekjoin_np() only peeks into the exit status of the specified thread. If the thread has not exited, the EBUSY error is returned. Otherwise, zero is returned and the thread exit value is optionally stored into the location of *value_ptr. The target thread is left unjoined and can be used as an argument for the pthread_join() family of functions again.

A thread that has exited but remains unjoined counts against [_POSIX_THREAD_THREADS_MAX].

RETURN VALUES

If successful, the described functions return zero. Otherwise an error number is returned to indicate the error or special condition.

ERRORS

The pthread_join(), pthread_peekjoin_np(), and pthread_timedjoin_np() functions will fail if:

[EINVAL]: The implementation has detected that the value specified by thread does not refer to a joinable thread.
[ESRCH]: No thread could be found corresponding to that specified by the given thread ID, thread.
[EDEADLK]: A deadlock was detected or the value of thread specifies the calling thread.
[EOPNOTSUPP]: The implementation detected that another caller is already waiting on thread.

Additionally, the pthread_timedjoin_np() function will fail if:

[ETIMEDOUT]: The specified absolute time passed while pthread_timedjoin_np() waited for thread exit.

The pthread_peekjoin_np() function will also fail if:

[EBUSY]: The specified thread has not yet exited.

STANDARDS

The pthread_join() function conforms to ISO/IEC 9945-1:1996 (“POSIX.1”). The pthread_timedjoin_np() function is a FreeBSD extension which first appeared in FreeBSD 6.1. Another extension, the pthread_peekjoin_np() function, first appearead in FreeBSD 13.0.