xv6 scheduler proc.c

void
scheduler(void)
{
  struct proc *p;
  int foundproc = 1;

  for(;;){
    // Enable interrupts on this processor.
    sti();


    int tickets_passed=0;
    int totalTickets = 0;

    for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){
      if(p->state != RUNNABLE)
        continue;
      totalTickets = totalTickets + p->tickets;
    }

    long winner = random_at_most(totalTickets);


    if (!foundproc) hlt();
    foundproc = 0;

    // Loop over process table looking for process to run.
    acquire(&ptable.lock);
    for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){
      if(p->state != RUNNABLE)
        continue;
      tickets_passed += p->tickets;
      if(tickets_passed<winner){
        continue;
      }
     // cprintf("tickets are : %d ,  rand no is %ld\n",p->tickets , random_at_most(10000));
      // Switch to chosen process.  It is the process's job
      // to release ptable.lock and then reacquire it
      // before jumping back to us.
      foundproc = 1;
      proc = p;
      switchuvm(p);
      p->state = RUNNING;
      swtch(&cpu->scheduler, proc->context);
      switchkvm();

      // Process is done running for now.
      // It should have changed its p->state before coming back.
      proc = 0;
      break;
    }
    release(&ptable.lock);

  }
}