Hi,
I have an atomic counter that gets incremented and decremented over
time (non monotonically).
At a certain point, I would like to enter a termination protocol where
increments are not possible anymore and I set an action to run if/when
the counter reaches zero.
Trivial when using synchronized/lock, but I'd like to give it a try
without them.
class A {
private final AtomicLong counter;
// Non-volatile
private Runnable action;
void terminate(Runnable action) {
this.action = action;
// Volatile write needed here for visibility.
if (counter.addAndGet(0) == 0) {
action.run();
}
}
void decrement() {
// Volatile read required to see this.action.
if (counter.decrementAndGet() == 0) {
Runnable a = this.action;
if (a != null) {
a.run()
}
}
}
}
Is addAndGet(0) a volatile write? Can the write be optimized away?
Similarly (although not relevant for this particular example), a
_failed_ compareAndSet() has the semantic of a volatile write even if
the set part was not done because the compare part failed?
Thanks!
--
Simone Bordet
---
Finally, no matter how good the architecture and design are,
to deliver bug-free software with optimal performance and reliability,
the implementation technique must be flawless. Victoria Livschitz
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