attilapiros commented on a change in pull request #24269: [SPARK-27341][CORE]
fix a deadlock between TaskMemoryManager and UnsafeExternalSorter
URL: https://github.com/apache/spark/pull/24269#discussion_r271297526
##########
File path:
core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeExternalSorter.java
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@@ -573,19 +573,29 @@ public boolean hasNext() {
@Override
public void loadNext() throws IOException {
- synchronized (this) {
- loaded = true;
- if (nextUpstream != null) {
- // Just consumed the last record from in memory iterator
- if (lastPage != null) {
- freePage(lastPage);
- lastPage = null;
+ MemoryBlock pageToFree = null;
+ try {
+ synchronized (this) {
+ loaded = true;
+ if (nextUpstream != null) {
+ // Just consumed the last record from in memory iterator
+ if (lastPage != null) {
+ // Do not free the page here, while we are locking
`SpillableIterator`. The `freePage`
+ // method locks the `TaskMemoryManager`, and it's a bad idea to
lock 2 objects in
+ // sequence. We may hit dead lock if another thread locks
`TaskMemoryManager` and
+ // `SpillableIterator` in sequence, which may happen in
+ // `TaskMemoryManager.acquireExecutionMemory`.
+ pageToFree = lastPage;
+ lastPage = null;
+ }
+ upstream = nextUpstream;
+ nextUpstream = null;
}
- upstream = nextUpstream;
- nextUpstream = null;
+ numRecords--;
+ upstream.loadNext();
}
- numRecords--;
- upstream.loadNext();
+ } finally {
+ if (pageToFree != null) freePage(pageToFree);
Review comment:
Nit: add braces (according to Oracle java style: `if statements always use
braces, {}`)
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