pthread_join() — Wait for a thread to end

Standards

Standards / Extensions	C or C++	Dependencies
POSIX.4a Single UNIX Specification, Version 3	both	POSIX(ON)

Format

#define _OPEN_THREADS
#include <pthread.h>

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

SUSV3:

#define _UNIX03_THREADS
#include <pthread.h>

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

General description

Allows the calling thread to wait for the ending of the target thread.

pthread_t is the data type used to uniquely identify a thread. It is returned by pthread_create() and used by the application in function calls that require a thread identifier.

status contains a pointer to the status argument passed by the ending thread as part of pthread_exit(). If the ending thread terminated with a return, status contains a pointer to the return value. If the thread was canceled, status can be set to -1.

Returned value

If successful, pthread_join() returns 0.

If unsuccessful, pthread_join() returns -1 and sets errno to one of the following values:

Error Code: Description
EDEADLK: A deadlock has been detected. This can occur if the target is directly or indirectly joined to the current thread.
EINVAL: The value specified by thread is not valid.
ESRCH: The value specified by thread does not refer to an undetached thread.

Notes:

When pthread_join() returns successfully, the target thread has been detached.
Multiple threads cannot use pthread_join() to wait for the same target thread to end. If a thread issues pthread_join() for a target thread after another thread has successfully issued pthread_join() for the same target thread, the second pthread_join() will be unsuccessful.
If the thread calling pthread_join() is canceled, the target thread is not detached.

Special behavior for Single UNIX Specification, Version 3: If unsuccessful, pthread_join() returns an error number to indicate the error.

Example

CELEBP32

/* CELEBP32 */
#define _OPEN_THREADS
#include <pthread.h>
#include <stdlib.h>
#include <stdio.h>

void *thread(void *arg) {
  char *ret;
  printf("thread() entered with argument '%s'\n", arg);
  if ((ret = (char*) malloc(20)) == NULL) {
    perror("malloc() error");
    exit(2);
  }
  strcpy(ret, "This is a test");
  pthread_exit(ret);
}

main() {
  pthread_t thid;
  void *ret;

  if (pthread_create(&thid, NULL, thread, "thread 1") != 0) {
    perror("pthread_create() error");
    exit(1);
  }

  if (pthread_join(thid, &ret) != 0) {
    perror("pthread_create() error");
    exit(3);
  }

  printf("thread exited with '%s'\n", ret);
}

Output:

thread() entered with argument 'thread 1'
thread exited with 'This is a test'