[GitHub] [hbase] Apache9 commented on a change in pull request #513: HBASE-22867 The ForkJoinPool in CleanerChore will spawn thousands of threads in our cluster with thousands table

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Apache9 commented on a change in pull request #513: HBASE-22867 The ForkJoinPool in CleanerChore will spawn thousands of threads in our cluster with thousands table
URL: https://github.com/apache/hbase/pull/513#discussion_r315609444
 
 

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 File path: hbase-server/src/main/java/org/apache/hadoop/hbase/master/cleaner/CleanerChore.java
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 @@ -423,16 +426,18 @@ protected Boolean compute() {
         allFilesDeleted = deleteAction(() -> checkAndDeleteFiles(files), "files");
       }
 
+      List<CompletableFuture<Boolean>> futures = new ArrayList<>();
       boolean allSubdirsDeleted = true;
       if (!subDirs.isEmpty()) {
-        List<CleanerTask> tasks = Lists.newArrayListWithCapacity(subDirs.size());
         sortByConsumedSpace(subDirs);
-        for (FileStatus subdir : subDirs) {
-          CleanerTask task = new CleanerTask(subdir, false);
-          tasks.add(task);
-          task.fork();
-        }
-        allSubdirsDeleted = deleteAction(() -> getCleanResult(tasks), "subdirs");
+        subDirs.forEach(dir -> futures.add(pool.execute(new CleanerTask(dir, false))));
 
 Review comment:
   I think submitting the task to the same pool is not safe here. In ForkJoinPool, it is safe to call join as in the join method, the current thread will try to execute tasks if there are any, so in general, we can always make progress and finally finish all the tasks. But here, the current thread will be blocked on the future.get, so it is possible that all the threads in the pool are blocked on a future.get and cause dead lock here.

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