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Update AbstractNodeQueue.java

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Avoid spinning on head when a peek/poll observes a null next but the queue is not empty.
This commit is contained in:
Nitsan Wakart 2014-07-28 14:19:34 +02:00
parent b88c964bd4
commit 5dbdc605b0
1 changed files with 9 additions and 5 deletions
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14
akka-actor/src/main/java/akka/dispatch/AbstractNodeQueue.java
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@ -29,12 +29,16 @@ public abstract class AbstractNodeQueue<T> extends AtomicReference<AbstractNodeQ
*/
@SuppressWarnings("unchecked")
protected final Node<T> peekNode() {
for(;;) {
final Node<T> tail = ((Node<T>)Unsafe.instance.getObjectVolatile(this, tailOffset));
final Node<T> next = tail.next();
if (next != null || get() == tail)
return next;
final Node<T> tail = ((Node<T>)Unsafe.instance.getObjectVolatile(this, tailOffset));
Node<T> next = tail.next();
if (next == null && get() != tail) {
// if tail != head this is not going to change until consumer makes progress
// we can avoid reading the head and just spin on next until it shows the f**k up
do {
next = tail.next();
} while (next == null);
}
return next;
}
public final T peek() {