Re: Multi-threading: wait for tasks to complete

markspace <>
Mon, 14 Dec 2009 10:57:07 -0800
Peter Duniho wrote:

While performance might not be an issue in all cases, I still would
probably have implemented your class with AtomicInteger, instead of
synchronized methods for countUp() and countDown(). Then you need only
synchronize when you actually need to notify. (The compare-and-set the
atomic classes implement aren't free of performance costs either, but
should generally perform better than a full lock).

Thanks for the feedback. I was hoping that synchronized methods in
UpDownLatch could be optimized to spin-locks at runtime, thus saving the
overhead of either a full lock or using AtomicInteger. However, I
haven't profiled it yet so I'm not sure that the synchronized methods
are better. It's certainly worthy of investigation.

I'd probably modify your idea as follows to avoid the explicit lock
object; the AtomicInteger can serve the same purpose (code is untested):

    private static class UpDownLatch2
       private AtomicInteger count = new AtomicInteger();
       public void countUp() {
       public void countDown() {
          synchronized( count ) {
             if( count.decrementAndGet() == 0 ) {
       public void await() throws InterruptedException {
          synchronized( count ) {
             while( count.get() != 0 ) {

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