Processes: Suspending a Process

• This is from section 23.4
  • I find knowledge of this section is useful for what we will do next.
  • Some of this chapter will not make sense as we have yet to discuss signals.
  • But a signal is just a notification of an extraordinary event
  • And we want processes before we get signals. (I think)
• Suspending a process
  • Tells the kernel that the process no longer wishes to run.
  • But may resume in the future.
  • This is not the same as

  • for(i=0;i&1000000;i++) {
    }
    	 

  • The above code continues to use CPU time to do nothing.
  • A suspended processes does not burn CPU time.
• There are several ways to suspend a process.
  • sleep
    • unsigned int sleep(unsigned int seconds);
    • Attempt to suspend the process for a fixed number of seconds
    • Return
      • 0: suspended for requested period of time.
      • >0: time to sleep remains.
    • If you are using alarms, this is probably not the ting to call.
    • If you are using timers, this is probably not the ting to call.
    • See code (mySleep.C).
      • top -p pid
      • kill -USR1 pid
  • usleep
    • int usleep(useconds_t usec);
    • Returns 0 (success), -1 (fail)
    • This call is obsolete, don't use it.
      • But you may see it.
      • Especially in my old code.
  • nanosleep
    • This is the modern way to sleep.
    • int nanosleep(const struct timespec *req, struct timespec *rem);
    • needs time.h

    • struct timespec {
           time_t tv_sec;        /* seconds */
           long   tv_nsec;       /* nanoseconds */
      };
      	    

    • This function does not rely on signals, alarms or timers.
    • Return 0 on success, 1 on error
    • On error, rem is the remaining time to sleep.
      • This is not change on success
    • Look at myNanoSleep.C