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Always synchronise on target for regionized queue mergeInto

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While for merging the synchronisation occured, it did not synchronise
for splitting. This resolves a possible CME that may occur while
splitting regions.
This commit is contained in:
Spottedleaf 2023-06-27 13:43:51 -07:00
parent 34039e3709
commit 81fe50f26f
1 changed files with 16 additions and 16 deletions
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32
patches/server/0003-Threaded-Regions.patch
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@ -4064,7 +4064,7 @@ index 0000000000000000000000000000000000000000..8e31c6ee9ee16aff699e124a9b0554ea
+}
diff --git a/src/main/java/io/papermc/paper/threadedregions/RegionizedTaskQueue.java b/src/main/java/io/papermc/paper/threadedregions/RegionizedTaskQueue.java
new file mode 100644
index 0000000000000000000000000000000000000000..2e4514e5a45db6e625ef7799b63a9285a3bc1030
index 0000000000000000000000000000000000000000..98ddb674b63a4777a98152ea960debf48aa2bc35
--- /dev/null
+++ b/src/main/java/io/papermc/paper/threadedregions/RegionizedTaskQueue.java
@@ -0,0 +1,768 @@
@ -4382,26 +4382,26 @@ index 0000000000000000000000000000000000000000..2e4514e5a45db6e625ef7799b63a9285
+ public void mergeInto(final PrioritisedQueue target) {
+ synchronized (this) {
+ this.isDestroyed = true;
+ synchronized (target) {
+ mergeInto(target, this.queues);
+ }
+ mergeInto(target, this.queues);
+ }
+ }
+
+ private static void mergeInto(final PrioritisedQueue target, final ArrayDeque<ChunkBasedPriorityTask>[] thisQueues) {
+ final ArrayDeque<ChunkBasedPriorityTask>[] otherQueues = target.queues;
+ for (int i = 0; i < thisQueues.length; ++i) {
+ final ArrayDeque<ChunkBasedPriorityTask> fromQ = thisQueues[i];
+ final ArrayDeque<ChunkBasedPriorityTask> intoQ = otherQueues[i];
+ synchronized (target) {
+ final ArrayDeque<ChunkBasedPriorityTask>[] otherQueues = target.queues;
+ for (int i = 0; i < thisQueues.length; ++i) {
+ final ArrayDeque<ChunkBasedPriorityTask> fromQ = thisQueues[i];
+ final ArrayDeque<ChunkBasedPriorityTask> intoQ = otherQueues[i];
+
+ // it is possible for another thread to queue tasks into the target queue before we do
+ // since only the ticking region can poll, we don't have to worry about it when they are being queued -
+ // but when we are merging, we need to ensure order is maintained (notwithstanding priority changes)
+ // we can ensure order is maintained by adding all of the tasks from the fromQ into the intoQ at the
+ // front of the queue, but we need to use descending iterator to ensure we do not reverse
+ // the order of elements from fromQ
+ for (final Iterator<ChunkBasedPriorityTask> iterator = fromQ.descendingIterator(); iterator.hasNext();) {
+ intoQ.addFirst(iterator.next());
+ // it is possible for another thread to queue tasks into the target queue before we do
+ // since only the ticking region can poll, we don't have to worry about it when they are being queued -
+ // but when we are merging, we need to ensure order is maintained (notwithstanding priority changes)
+ // we can ensure order is maintained by adding all of the tasks from the fromQ into the intoQ at the
+ // front of the queue, but we need to use descending iterator to ensure we do not reverse
+ // the order of elements from fromQ
+ for (final Iterator<ChunkBasedPriorityTask> iterator = fromQ.descendingIterator(); iterator.hasNext();) {
+ intoQ.addFirst(iterator.next());
+ }
+ }
+ }
+ }