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Set prev to null when setting cursor to head in scavengeSome.

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Motivation:

`scavengeSome()` has a corner case: when setting `cursor` to `head`, `this.prev` may point to the tail of the  `WeakOrderQueue` linked list. Then it's possible that the following while loop will link the tail to the head, and cause endless loop.

I made a reproducer in 36522e7b72 . The unit test will just run forever. Unfortunately, I cannot change it to a unit test because it needs to add some codes to `scavengeSome` to control the execution flow.

Modification:

Set `prev` to null when setting `cursor` to `head` in `scavengeSome`

Result:

Fixes #6153.
This commit is contained in:
Shixiong Zhu 2017-01-06 13:12:43 -08:00 committed by Norman Maurer
parent a8950dfc4c
commit 2457f386d8
1 changed files with 4 additions and 1 deletions
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5
common/src/main/java/io/netty/util/Recycler.java
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@ -479,16 +479,19 @@ public abstract class Recycler<T> {
} }
boolean scavengeSome() { boolean scavengeSome() {
WeakOrderQueue prev;
WeakOrderQueue cursor = this.cursor; WeakOrderQueue cursor = this.cursor;
if (cursor == null) { if (cursor == null) {
prev = null;
cursor = head; cursor = head;
if (cursor == null) { if (cursor == null) {
return false; return false;
} }
} else {
prev = this.prev;
} }
boolean success = false; boolean success = false;
WeakOrderQueue prev = this.prev;
do { do {
if (cursor.transfer(this)) { if (cursor.transfer(this)) {
success = true; success = true;