Question

pthread_create returns the value 251 without creating the thread. Does anyone know what the problem is? Please help. The machine is a HP-UX.

I’m new to multi-threading.

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

   void *print_message_function( void *ptr );

   main()
   {
        pthread_t thread1, thread2;
        char *message1 = "Thread 1";
        char *message2 = "Thread 2";
        int  iret1, iret2;
        /* Create independent threads each of which will
         * execute function */

        iret1 = pthread_create( &thread1, NULL, print_message_function, (void*) message1);
        iret2 = pthread_create( &thread2, NULL, print_message_function, (void*) message2);

        /* Wait till threads are complete before
         * main continues. Unless we  */
        /* wait we run the risk of executing an
         * exit which will terminate   */
        /* the process and all threads before the
         * threads have completed.   */

        pthread_join( thread1, NULL);
        pthread_join( thread2, NULL);
        printf("Thread 1 returns: %d\n",iret1);
        printf("Thread 2 returns: %d\n",iret2);
        exit(0);
   }

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

Answer 1

Edit : On HP-UX11. pthread_create is failing with error 251: Function is not available.

Check whether -lc comes before -lpthread in your link order.
If this is the case, then the call would resolve to stub in C-library
and could cause this error.

---

Did you link with -lpthread?

You should use errno.h to see what error 251 is on your system or this should give you a more detailled message :

printf("%s\n", strerror(errno));

Moreover, when using pthread, you should check for the return value of almost every call to pthread* (see the man of every function to check for possible error returned)

For pthread_create, you have at least 2 possible errors (depending on your system and pthread implementation) :

pthread_create() will fail if:

[EAGAIN] The system lacked the necessary resources to create
another thread, or the system-imposed limit on the
total number of threads in a process
[PTHREAD_THREADS_MAX] would be exceeded.

[EINVAL] The value specified by attr is invalid.