/**
* Spins/yields/blocks until node s is matched or caller gives up.
*
* @param s the waiting node
* @param pred the predecessor of s, or s itself if it has no predecessor, or null if unknown (the
* null case does not occur in any current calls but may in possible future extensions)
* @param e the comparison value for checking match
* @param timed if true, wait only until timeout elapses
* @param nanos timeout in nanosecs, used only if timed is true
* @return matched item, or e if unmatched on interrupt or timeout
*/
private Message awaitMatch(Node s, Node pred, Message e, boolean timed, long nanos)
throws SuspendExecution {
long lastTime = timed ? System.nanoTime() : 0L;
Strand w = Strand.currentStrand();
int spins =
(w.isFiber()
? 0
: -1); // no spins in fiber; otherwise, initialized after first item and cancel checks
ThreadLocalRandom randomYields = null; // bound if needed
if (spins == 0) requestUnpark(s, w);
for (; ; ) {
Object item = s.item;
if (item == CHANNEL_CLOSED) setReceiveClosed();
if (item != e) { // matched
// assert item != s;
s.forgetContents(); // avoid garbage
return this.<Message>cast(item);
}
if ((w.isInterrupted() || (timed && nanos <= 0)) && s.casItem(e, s)) { // cancel
unsplice(pred, s);
return e;
}
if (spins < 0) { // establish spins at/near front
if ((spins = spinsFor(pred, s.isData)) > 0) randomYields = ThreadLocalRandom.current();
} else if (spins > 0) { // spin
--spins;
if (randomYields.nextInt(CHAINED_SPINS) == 0) Strand.yield(); // occasionally yield
} else if (s.waiter == null) {
requestUnpark(s, w); // request unpark then recheck
} else if (timed) {
long now = System.nanoTime();
if ((nanos -= now - lastTime) > 0) Strand.parkNanos(this, nanos);
lastTime = now;
} else {
Strand.park(this);
}
}
}
