Prevent ConcurrentModificationException for PushOne.refBatchesToPush

The PushOne.refBatchesToPush was a plain HashSet but r/w access to it
wasn't synchronized. Under some circumstances, traversing a stream
created on refBatchesToPush threw ConcurrentModificationException [1]
which caused the thread to die. As a side effect of the thread-death,
the replication task would never reschedule itself but would remain in
the pending tasks and all follow-up replications to the same URI would
be consolidated into that pending task which would never run. Only a
restart of the replication plugin would resolve the issue.

[1]
ERROR com.google.gerrit.server.git.WorkQueue : WorkQueue thread ReplicateTo-some-uri-2 threw exception
java.util.ConcurrentModificationException
        at java.base/java.util.HashMap$KeySpliterator.tryAdvance(HashMap.java:1730)
        at java.base/java.util.stream.ReferencePipeline.forEachWithCancel(ReferencePipeline.java:129)
        at java.base/java.util.stream.AbstractPipeline.copyIntoWithCancel(AbstractPipeline.java:527)
        at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:513)
        at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499)
        at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:921)
        at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
        at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:682)
        at com.googlesource.gerrit.plugins.replication.PushOne.getLimitedRefs(PushOne.java:255)
        at com.googlesource.gerrit.plugins.replication.PushOne.toString(PushOne.java:221)
        at com.google.gerrit.server.git.WorkQueue$ProjectTask.toString(WorkQueue.java:760)
        at java.base/java.lang.StringConcatHelper.stringOf(StringConcatHelper.java:453)
        at com.google.gerrit.server.git.WorkQueue$Task.run(WorkQueue.java:678)
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
        at java.base/java.lang.Thread.run(Thread.java:840)

Change-Id: I3f29779fd150868412e4994d307303d1dd8bde7b

1 files changed, 1 insertions, 1 deletions

diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/PushOne.java b/src/main/java/com/googlesource/gerrit/plugins/replication/PushOne.java
index ed84087..c25f375 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/PushOne.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/PushOne.java
@@ -122,7 +122,7 @@ class PushOne implements ProjectRunnable, CanceledWhileRunning, UriUpdates {
 
   private final Project.NameKey projectName;
   private final URIish uri;
-  private final Set<ImmutableSet<String>> refBatchesToPush = Sets.newHashSetWithExpectedSize(4);
+  private final Set<ImmutableSet<String>> refBatchesToPush = Sets.newConcurrentHashSet();
   private boolean pushAllRefs;
   private Repository git;
   private boolean isCollision;