pthread_join example c c++

PTHREAD_JOIN(3)          BSD Library Functions Manual          PTHREAD_JOIN(3)

NAME
     pthread_join -- wait for thread termination

SYNOPSIS
     #include <pthread.h>

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

DESCRIPTION
     The pthread_join() function suspends execution of the calling thread until the target thread termi-
     nates, 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, the target thread is not detached.

RETURN VALUES
     If successful,  the pthread_join() function will return zero.  Otherwise, an error number will be
     returned to indicate the error.

ERRORS
     pthread_join() will fail if:

     [EDEADLK]          A deadlock was detected or the value of thread specifies the calling thread.

     [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.

SEE ALSO
     wait(2), pthread_create(3)

STANDARDS
     pthread_join() conforms to ISO/IEC 9945-1:1996 (``POSIX.1'').

Example of pthread_join

#include <pthread.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>

void *t_function(void *data)
{
    int num = *((int *)data);
    printf("num %d\n", num);
    sleep(1);
    return (void *)(num*num);
}

int main()
{
    pthread_t p_thread;
    int thr_id;
    int status;
    int a = 100;

    thr_id = pthread_create(&p_thread, NULL, t_function, (void *)&a);
    if (thr_id < 0)
    {
        perror("thread create error : ");
        exit(0);
    }

    pthread_join(p_thread, (void *)&status);
    printf("thread join : %d\n", status);

    return 0;
}