Implementing a blocking loop (Java or C)

Miaire · 04-28-2005, 12:45 AM

I am not sure about the term I used but what I'm thinking about is something like this. I want to have a loop which will continue to loop until a certain variable, say a boolean becomes change.

Code:

while( locked ){
 // nothing
}

Then on another part of the code, on perhaps a thread, it will set locked to false so the code will break free from the loop and continue on. But I seem to notice that it eats up a lot of processing power, so I set up sleep for a few milliseconds, like in Java:

Code:

while(locked ){
    try{
        Thread.currentThread().sleep(100);
    }
    catch( InterruptedException e ){
    }
}

I was wondering if there's a better way of implementing something like this in Java. Something that is much more punctual than a given amount of time (in that example, 100ms) and something that doesn't consume as much computer processing power. And maybe also something for C because I'm curious. Thanks a lot.

ilikejam · 04-28-2005, 01:30 AM

Hi.

This is built into Java. Have a look at the notify() and wait() methods on this page:
http://java.sun.com/j2se/1.5.0/docs/...ng/Object.html

Dave

Miaire · 04-28-2005, 01:49 AM

Quote:

Originally posted by ilikejam
This is built into Java. Have a look at the notify() and wait() methods on this page:
http://java.sun.com/j2se/1.5.0/docs/...ng/Object.html

Thanks for your reply, I didn't know that was the purpose of it. I implemented it but I'm still left wondering because it throws IllegalMonitorStateException when I use another thread to notify() after I used wait() on another thread. I was wondering if I'm just supposed to catch it.

= Edit: hold on I think I made a mistake somewhere, checking my mistake first, please ignore this.

ilikejam · 04-28-2005, 02:09 AM

No, it shouldn't throw that error. It's ages since I did anything multithreaded in Java, so I'm not sure of the details.

Looking at the description for wait():

Code:

synchronized (obj) {
         while (<condition does not hold>)
             obj.wait(); //you probably want wait(), not wait(int timeout) here
         ... // Perform action appropriate to condition
     }

is something like what you're looking for. To wake the thread, you'd use 'obj.notifyAll()'

Don't quote me on that though...

Dave

rstewart · 04-28-2005, 02:22 PM

In C or C++ you would use some sort of semaphore or mutex. The specific functions to call are dependent upon what "style" of code you are writing. If simple multiprocessing you could use the IPC "semctl()", "semget()", and "semop()" functions. If multithreading (using pthreads) you could use "pthread_mutex_init()", "pthread_mutex_lock()", "pthread_mutex_unlock()", and "pthread_mutex_destroy()" for mutex locks (You could then use those primitives to create your own semaphore library).