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

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.