topic Re: Anyway to prevent busy waiting? in Operating System - HP-UX

Anyway to prevent busy waiting?

Henry Chua — Tue, 22 Feb 2005 19:49:39 GMT

I got a program which is written to wait for a condition to be meet before it will proceed with its job
say:
while (TRUE){
if ( Condition = TRUE){
do procedure();
}
}
so it will loop endlessly waiting for the condition to be met. Is there any other way to do this preventing unnecessary tying up of the CPU? Semaphore maybe?

Re: Anyway to prevent busy waiting?

TwoProc — Tue, 22 Feb 2005 20:04:30 GMT

Well, you could put in a sleep command in your loop - "sleep 60" inside of your loop will make the loop wait 1 minute before continuing with the next check...

Re: Anyway to prevent busy waiting?

Henry Chua — Tue, 22 Feb 2005 21:23:01 GMT

Hi John, thanks for the input. Just for my info, is there anyway I can run the process on the background and let it behave like an interrupt so that it will not tied un unnecessary CPU time but yet constantly waiting for the right condition?

Re: Anyway to prevent busy waiting?

A. Clay Stephenson — Tue, 22 Feb 2005 21:47:17 GMT

Semaphores are made to do this sort of thing. In your case, your would do a semop with IPC_NOWAIT set to false so that the process is suspended until another cooperating process adjusts the semval. Man semop for details. The other mechansism that you might want to use is wait(). The idea is that you would spawn a child process to do some processing and then exit and that would reawaken the calling process. Man 2 wait for details.

Re: Anyway to prevent busy waiting?

Henry Chua — Tue, 22 Feb 2005 22:52:20 GMT

Hi Stephenson,

Thanks for the info. Just a thought, if the cue for the execution of the procedure lies in whether a file is modified or not. Is it possible to utilise sempahore in this application? this seems to be a gray as the file may not be tied up by any process most of the time..

regards
Henry

Re: Anyway to prevent busy waiting?

A. Clay Stephenson — Wed, 23 Feb 2005 09:56:07 GMT

While a file can serve the purpose of a semaphore, it would have the same problem as your original code. The only way to know if a file has been modified is to test in a loop. Unlike with semaphores, there is no mechanism to "wake" a process when a file has been modified.

Re: Anyway to prevent busy waiting?

Henry Chua — Wed, 23 Feb 2005 22:28:09 GMT

Thank guys for all your input, guess i still have to resort to using a loop at the end of the day..