Description: Please refer to section 6.8.
Deadline: 2010 May 6 00:05am
Put your file(s) under ~/usp-982/exer7

This exercise asks you to write a barrier-server and a function used in barrier-client.
The pseudo code for client is (The protocal is run three times.)

          void waitatbarrier(char *barrier)
          {
           .....
          }

          main(int argc, char *argv[])
          {
            srand48(getpid());
            for(j=0;j<3;j++){
              sleep((int) (20*drand48()));
              fprintf(stderr, "Waked up! Waiting for others\n");
              waitatbarrier(argv[1]);
              fprintf(stderr, "*** All waked up. *** Do something.\n");
            }
          }

For example:

          $ ./barrier-server ok 4      <----- this is the server
          ....
          $

          $ ./barrier-client ok      <---- This is one of the four clients.
          Waked up! Waiting for others
          *** All waked up. *** Do something.
          Waked up! Waiting for others
          *** All waked up. *** Do something.
          Waked up! Waiting for others
          *** All waked up. *** Do something.
          $