/* Programming Assignment 1: Exercise C
*
* Now we will learn how to effect the execution sequence of the various
* processes. We introduce a new system call (not present in Unix) called
* Yield (pid), which causes the currently running process to yield to the
* process whose identifier is pid. Furthermore, when Yield (pid) returns,
* it returns the identifier of the process that yielded to the one that is
* now running (and returning from Yield (pid)). This is illustrated by the
* program below, which you should study and run.
*
* Questions
*
* 1. Can you explain the order of what gets printed based on the code?
*
*/
#include <stdio.h>
#include "aux.h"
#include "umix.h"
void Main ()
{
int pid = 0, rpid;
if ((pid = Fork ()) == 0) {
/* first child executes here */
Printf ("I am the first child, my pid is %d\n", Getpid ());
Exit ();
}
Printf ("I am the parent, my pid is %d\n", Getpid ());
Printf ("About to yield to child process whose pid is %d\n", pid);
rpid = Yield (pid); /* yield to first child before continuing */
Printf ("Process %d just yielded to me (the parent)\n", rpid);
if ((pid = Fork ()) == 0) {
/* second child executes here */
Printf ("I am the second child, my pid is %d\n", Getpid ());
Exit ();
}
Printf ("About to yield to child process whose pid is %d\n", pid);
rpid = Yield (pid); /* yield to second child before continuing */
Printf ("Process %d just yielded to me (the parent)\n", rpid);
}
