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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").
>
> Penelope is a thread, as are her suitors. Penelope has plenty to do
> after she delivers her verdict, so the verdict is not a return value -
> it's a value she'll pass to a method. In code, this looks something like:
>
> class Penelope implements Runnable {
> public void run() {
> try {
> Verdict v = ... ;
> DELIVER(v);
> }
> catch (Exception e) {
> DELIVER_EXCEPTION(e);
> }
> }
> }
>
> class Suitor implements Runnable() {
> public void run() {
> try {
> Verdict v = AWAIT();
> }
> catch (Exception e) {
> // alas
> }
> }
> }
>
> There has got to be something in java.util.concurrent that she can use
> to deliver her verdict. What?
>
> In terms of synchronisation, CountdownLatch with a count of 1 does it -
> the suitors await, and Penelope counts down. But it has no way to pass a
> value.

In any case, I would wrap the verdict delivery issues up in a class so
that neither Penelope nor the suitors need to know about the
synchronization implementation.

Within that class, I would probably use ordinary fields to represent the
verdict, exceptional or otherwise.

One way to do the synchronization would be a semaphore that is initially
zero, but with a large number of permits added when Penelope calls a
setVerdict method. The getVerdict method that the suitors call would
wait to get a permit, record the verdict, and put the permit back so
there is no possibility of running out of permits.

Patricia

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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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