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lufthansa747

Sun Sep 11, 2011 10:43 pm


Help with Java Semiphore

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ok what i am trying to do with the semiphore is. i want to init it and for every thread i make i want to increase the count by 1. when the thread is done i want to decrease the count by 1. while all this is happening i want the main thread to wait untill the semphore has reached and count of 0 and then continue with the code. how can i do this.


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lufthansa747

Mon Sep 12, 2011 7:39 am


Re: Help with Java Semiphore

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bump


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S_Grimm

Mon Sep 12, 2011 8:29 am


RE:Help with Java Semiphore

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http://www.javaworld.com/javaworld/jw-04-1996/jw-04-threads.html?page=2

try using that code but with a counter instead of the boolean variable.

eg [code] if (counter > 1)
{
threadOne.suspend();
}
else
{
threadOne.resume();
}
[/code]

and have your other threads increment the counter when they are called.

edit: you'd have to stick it in a block of code that isn't mouseDown()


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Tony

Mon Sep 12, 2011 8:35 am


RE:Help with Java Semiphore

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A semaphore is typically used to block until a resource becomes available (continue with code when a count is above 0), but I suppose you can inverse the condition.

The only tricky part to the implementation are atomic increment/decrement operations, but then there's java.util.concurrent.atomic


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lufthansa747

Mon Sep 12, 2011 2:00 pm


Re: RE:Help with Java Semiphore

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A semaphore is typically used to block until a resource becomes available (continue with code when a count is above 0), but I suppose you can inverse the condition.

The only tricky part to the implementation are atomic increment/decrement operations, but then there's java.util.concurrent.atomic

well this is why i want to do that. i have one main thread. that thread spawn off 9 other threads which all do there own math operations. when they are done they update the main thread with numbers and decrement a variable in the main thread which keeps track of alive threads. currently i have my main thread stuck in a while loop with a 1 millisecond sleep waiting for the other threads to finish. i was hopping that using a semphore could optimize the code a bit because it would be more efficient then calling thread.sleep?


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Tony

Mon Sep 12, 2011 2:06 pm


RE:Help with Java Semiphore

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With a semaphore, you would still be busy-waiting.


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lufthansa747

Mon Sep 12, 2011 2:42 pm


Re: RE:Help with Java Semiphore

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With a semaphore, you would still be busy-waiting.

but wouldn't it be faster and more efficient


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Tony

Mon Sep 12, 2011 2:59 pm


RE:Help with Java Semiphore

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Than what? How are you checking that other threads have finished now? How is that different from what you plan on doing?


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lufthansa747

Mon Sep 12, 2011 5:58 pm


Re: RE:Help with Java Semiphore

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Than what? How are you checking that other threads have finished now? How is that different from what you plan on doing?


the code currently looks like this

while(threadCount != 0){
     Thread.Sleep(1);
}

//do something her


but i thought that if i could use a semiphore block it would be better because i would not be doing a tight loop. lol idk i just though it would be better.


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DemonWasp

Mon Sep 12, 2011 8:47 pm


RE:Help with Java Semiphore

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In Java, if you want to wait for another thread to complete, use .join() on the thread you want to wait for. See: http://download.oracle.com/javase/6/docs/api/java/lang/Thread.html

Your main then looks like:


List threads = ... // your code here...

// Start all threads...
for ( Thread thread : threads ) {
    thread.start();
}

// Wait until all threads are done...
for ( Thread thread : threads ) {
    thread.join();
}


Join puts the calling thread to sleep until the target thread is done. This is done without a busy-wait.