Multiple execution of same thread subroutine on commenting pthread_join for that thread [duplicate]

Answer 1

Perhaps the output buffer is not flushing correctly. I've encountered a very similar issue when doing multithreading and piping the output to a file--sometimes output would appear twice. Try adding this line to your main function:

setvbuf(stdout, NULL, _IONBF, 0);

This will force the output buffer to be flushed on each write.

Answer 2

If I am getting these results, first of all I would do the following:

1) Instead of below lines,

iret1 = pthread_create( &thread1, NULL, print_message_function, (void*) message1);

iret2 = pthread_create( &thread2, NULL, print_message_function, (void*) message2);
pthread_join( thread1, NULL);

pthread_join( thread2, NULL); 

replace it with,

iret1 = pthread_create( &thread1, NULL, print_message_function, (void*) message1);

pthread_join( thread1, NULL);
iret2 = pthread_create( &thread2, NULL, print_message_function, (void*) message2);

pthread_join( thread2, NULL); 

and see what is the result.

2) Inside your thread function, you need to call pthread_exit("Exit"); This is a proper way to exit from the thread function. Do it at the end of function.

void *print_message_function( void *ptr )
{
        char *message;
        message = (char *) ptr;
        printf("%s \n", message);
        pthread_exit("Exit"); 
    }

If you are doing it this way, ideally you should not face any problem. In every case, i am assuming you are compiling your program using gcc -D_REENTRANT -o threadex threadex.c -lpthread

This is not the final solution. If it is going well, then we can proceed to next step of starting both the threads at a time.

Please share the feedback after incorporating these changes.