/**
* Spins/blocks until node s is matched by a fulfill operation.
*
* @param s the waiting node
* @param timed true if timed wait
* @param nanos timeout value
* @return matched node, or s if cancelled
*/
SNode awaitFulfill(SNode s, boolean timed, long nanos) {
/*
* When a node/thread is about to block, it sets its waiter
* field and then rechecks state at least one more time
* before actually parking, thus covering race vs
* fulfiller noticing that waiter is non-null so should be
* woken.
*
* When invoked by nodes that appear at the point of call
* to be at the head of the stack, calls to park are
* preceded by spins to avoid blocking when producers and
* consumers are arriving very close in time. This can
* happen enough to bother only on multiprocessors.
*
* The order of checks for returning out of main loop
* reflects fact that interrupts have precedence over
* normal returns, which have precedence over
* timeouts. (So, on timeout, one last check for match is
* done before giving up.) Except that calls from untimed
* SynchronousQueue.{poll/offer} don't check interrupts
* and don't wait at all, so are trapped in transfer
* method rather than calling awaitFulfill.
*/
long lastTime = timed ? System.nanoTime() : 0;
Thread w = Thread.currentThread();
SNode h = head;
int spins = (shouldSpin(s) ? (timed ? maxTimedSpins : maxUntimedSpins) : 0);
for (; ; ) {
if (w.isInterrupted()) s.tryCancel();
SNode m = s.match;
if (m != null) return m;
if (timed) {
long now = System.nanoTime();
nanos -= now - lastTime;
lastTime = now;
if (nanos <= 0) {
s.tryCancel();
continue;
}
}
if (spins > 0) spins = shouldSpin(s) ? (spins - 1) : 0;
else if (s.waiter == null) s.waiter = w; // establish waiter so can park next iter
else if (!timed) LockSupport.park(this);
else if (nanos > spinForTimeoutThreshold) LockSupport.parkNanos(this, nanos);
}
}
/**
* Spins/blocks until node s is fulfilled.
*
* @param s the waiting node
* @param e the comparison value for checking match
* @param timed true if timed wait
* @param nanos timeout value
* @return matched item, or s if cancelled
*/
Object awaitFulfill(QNode s, Object e, boolean timed, long nanos) {
/* Same idea as TransferStack.awaitFulfill */
long lastTime = timed ? System.nanoTime() : 0;
Thread w = Thread.currentThread();
int spins = ((head.next == s) ? (timed ? maxTimedSpins : maxUntimedSpins) : 0);
for (; ; ) {
if (w.isInterrupted()) s.tryCancel(e);
Object x = s.item;
if (x != e) return x;
if (timed) {
long now = System.nanoTime();
nanos -= now - lastTime;
lastTime = now;
if (nanos <= 0) {
s.tryCancel(e);
continue;
}
}
if (spins > 0) --spins;
else if (s.waiter == null) s.waiter = w;
else if (!timed) LockSupport.park(this);
else if (nanos > spinForTimeoutThreshold) LockSupport.parkNanos(this, nanos);
}
}
