Help with Java Semiphore

[lufthansa747]

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.

[lufthansa747]

bump

[S_Grimm]

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(); }

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()

[Tony]

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

[lufthansa747]

Tony @ Mon Sep 12, 2011 8:35 am wrote:

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?

[Tony]

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

[lufthansa747]

Tony @ Mon Sep 12, 2011 2:06 pm wrote:

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

but wouldn't it be faster and more efficient

[Tony]

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

[lufthansa747]

Tony @ Mon Sep 12, 2011 2:59 pm wrote:

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.

[DemonWasp]

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:

Java:

List<Thread> 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.