[GitHub] [hadoop] ZanderXu commented on a diff in pull request #5033: HDFS-16804. AddVolume contains a race condition with shutdown block pool

[GitBox <gi...@apache.org>]

ZanderXu commented on code in PR #5033:
URL: https://github.com/apache/hadoop/pull/5033#discussion_r1010020543


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hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/ReplicaMap.java:
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@@ -166,25 +167,24 @@ void addAll(ReplicaMap other) {
   /**
    * Merge all entries from the given replica map into the local replica map.
    */
-  void mergeAll(ReplicaMap other) {
+  void mergeAll(ReplicaMap other) throws IOException {
     Set<String> bplist = other.map.keySet();
     for (String bp : bplist) {
       checkBlockPool(bp);
       try (AutoCloseDataSetLock l = lockManager.writeLock(LockLevel.BLOCK_POOl, bp)) {
         LightWeightResizableGSet<Block, ReplicaInfo> replicaInfos = other.map.get(bp);
         LightWeightResizableGSet<Block, ReplicaInfo> curSet = map.get(bp);
+        if (curSet == null) {
+          // Can't find the block pool id in the replicaMap. Maybe it has been removed.

Review Comment:
   @DaveTeng0 Thanks for your review.
   
   > is it possible we can't find block pool id from the map, but the block pool is not removed yet?
   
   I think it's impossible. If you find some cases, please share.
   
   1. The `mergeAll` method only been used by the `activateVolume` method with a `synchronized` lock.
   2. The `shutdownBlockPool` method only been used by the `shutdownBlockPool` method with a `synchronized` lock, which beed added in this PR.
   3. The `addBlockPool` method always initialize an empty `LightWeightResizableGSet` in the global `ReplicaMap` for this block pool.



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