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Avoid redundant reads of head in peakNode

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Motivation:

There is not need todo redunant reads of head in peakNode as we can just spin on next() until it becomes visible.

Modifications:

Remove redundant reads of head in peakNode. This is based on @nitsanw's patch for akka.
See https://github.com/akka/akka/pull/15596

Result:

Less volatile access.
This commit is contained in:
Norman Maurer 2014-08-18 08:35:25 +02:00
parent 16a8f8b5aa
commit a32652197b
1 changed files with 11 additions and 14 deletions
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25
common/src/main/java/io/netty/util/internal/MpscLinkedQueue.java
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@ -97,21 +97,18 @@ final class MpscLinkedQueue<E> extends MpscLinkedQueueTailRef<E> implements Queu
* Returns the node right next to the head, which contains the first element of this queue. * Returns the node right next to the head, which contains the first element of this queue.
*/ */
private MpscLinkedQueueNode<E> peekNode() { private MpscLinkedQueueNode<E> peekNode() {
for (;;) { MpscLinkedQueueNode<E> head = headRef();
final MpscLinkedQueueNode<E> head = headRef(); MpscLinkedQueueNode<E> next = head.next();
final MpscLinkedQueueNode<E> next = head.next(); if (next == null && head != tailRef()) {
if (next != null) { // if tail != head this is not going to change until consumer makes progress
return next; // we can avoid reading the head and just spin on next until it shows up
} //
if (head == tailRef()) { // See https://github.com/akka/akka/pull/15596
return null; do {
} next = head.next();
} while (next == null);
// If we are here, it means:
// * offer() is adding the first element, and
// * it's between replaceTail(newTail) and oldTail.setNext(newTail).
// (i.e. next == oldTail and oldTail.next == null and head == oldTail != newTail)
} }
return next;
} }
@Override @Override