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Re: Making one or more threads wait for another to produce a value or fail

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On 5/31/2011 7:00 AM, Tom Anderson wrote:
> The scenario:
>
> Penelope is a widow, or at least her husband isn't around any more
> (she's not sure which; long story). There are 108 suitors who would like
> to marry her. She hasn't decided which one she'll marry. So, the 108
> suitors are sitting about waiting for her to decide. It's possible that
> instead of deciding to marry one of them, she'll deliver some other,
> exceptional, verdict (eg "turns out my husband is still alive, and will
> now murder you all").


Just popping in quickly.  First, everyone's all about CountDownLatch. 
Does this really work?  It requires a fixed number of threads supplied 
on creation to "fire," iirc.

Second what about other java.util.concurrent classes?  Both locks (esp 
ReadWriteLock) and AbstractQueuedSynchronizer look promising.

<http://download.oracle.com/javase/6/docs/api/java/util/concurrent/locks/AbstractQueuedSynchronizer.html>

Especially the second example for AQS, which is "a latch class that is 
like a CountDownLatch except that it only requires a single signal to 
fire. Because a latch is non-exclusive, it uses the shared acquire and 
release methods."


Lastly, I must be dense, I have a simple implementation but I think it's 
wrong.  What is wrong with it?  I'm sure I've missed something in the 
original specification, but I'm drawing a blank.  How is the exceptional 
verdict delivered?  There's also no way to set a verdict for one thread 
vs setting a return value for all threads.  I think your initial 
specification of using just "await()" and "deliver()" might be a bit too 
simple for the problem.

This is just a simple class that sends a single message (the verdict) to 
all threads (i.e., it broadcasts the message).  Note this is untested.


public class BroadcastSynchronizer<V, E extends Throwable> {

     private volatile V verdict;
     private final Object lock = new Object();

     public V await() throws E, InterruptedException {
         while( verdict == null ) {
             synchronized( lock ) {
                 if( verdict == null )
                     lock.wait();
             }
         }
         return verdict;
     }

     public void deliver( V verdict ) {
         this.verdict = verdict;
         synchronized( lock ) {
            lock.notifyAll();
         }
     }
}

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Making one or more threads wait for another to produce a value or fail Tom Anderson <twic@urchin.earth.li> - 2011-05-31 15:00 +0100
  Re: Making one or more threads wait for another to produce a value or fail Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-05-31 07:14 -0700
    Re: Making one or more threads wait for another to produce a value or fail Tom Anderson <twic@urchin.earth.li> - 2011-05-31 16:46 +0100
      Re: Making one or more threads wait for another to produce a value or fail Deeyana <d.awlberg@hotmail.invalid> - 2011-05-31 19:23 +0000
        Re: Making one or more threads wait for another to produce a value or fail Tom Anderson <twic@urchin.earth.li> - 2011-06-01 22:12 +0100
      Re: Making one or more threads wait for another to produce a value or fail Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-05-31 20:45 -0700
        Re: Making one or more threads wait for another to produce a value or fail Patricia Shanahan <pats@acm.org> - 2011-05-31 21:37 -0700
          Re: Making one or more threads wait for another to produce a value or fail Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-06-01 07:18 -0700
            Re: Making one or more threads wait for another to produce a value or fail Patricia Shanahan <pats@acm.org> - 2011-06-01 09:01 -0700
        Re: Making one or more threads wait for another to produce a value or fail Lawrence D'Oliveiro <ldo@geek-central.gen.new_zealand> - 2011-06-01 16:40 +1200
          Re: Making one or more threads wait for another to produce a value or fail "John B. Matthews" <nospam@nospam.invalid> - 2011-06-01 11:22 -0400
            Re: Making one or more threads wait for another to produce a value or fail Lawrence D'Oliveiro <ldo@geek-central.gen.new_zealand> - 2011-06-02 10:15 +1200
              Re: Making one or more threads wait for another to produce a value or fail "John B. Matthews" <nospam@nospam.invalid> - 2011-06-01 21:38 -0400
        Re: Making one or more threads wait for another to produce a value or fail Tom Anderson <twic@urchin.earth.li> - 2011-06-01 22:07 +0100
          Re: Making one or more threads wait for another to produce a value or fail Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-06-01 22:46 -0700
  Re: Making one or more threads wait for another to produce a value or fail markspace <-@.> - 2011-05-31 08:26 -0700
    Re: Making one or more threads wait for another to produce a value or fail Tom Anderson <twic@urchin.earth.li> - 2011-05-31 19:13 +0100
  Re: Making one or more threads wait for another to produce a value or fail Patricia Shanahan <pats@acm.org> - 2011-05-31 09:06 -0700
    Re: Making one or more threads wait for another to produce a value or fail Paul Cager <paul.cager@googlemail.com> - 2011-05-31 10:08 -0700
      Re: Making one or more threads wait for another to produce a value or fail Patricia Shanahan <pats@acm.org> - 2011-05-31 10:39 -0700
        Re: Making one or more threads wait for another to produce a value or fail Paul Cager <paul.cager@googlemail.com> - 2011-05-31 16:24 -0700
  Re: Making one or more threads wait for another to produce a value or fail Lawrence D'Oliveiro <ldo@geek-central.gen.new_zealand> - 2011-06-01 12:33 +1200
    Re: Making one or more threads wait for another to produce a value or fail "John B. Matthews" <nospam@nospam.invalid> - 2011-06-01 00:38 -0400
  Re: Making one or more threads wait for another to produce a value or fail markspace <-@.> - 2011-06-02 14:10 -0700
    Re: Making one or more threads wait for another to produce a value or fail markspace <-@.> - 2011-06-02 14:25 -0700
    Re: Making one or more threads wait for another to produce a value or fail Patricia Shanahan <pats@acm.org> - 2011-06-02 14:43 -0700

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