[GitHub] [pulsar] labuladong commented on a diff in pull request #18340: [fix][ml]fix wrong cursor state if repeat do close

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

labuladong commented on code in PR #18340:
URL: https://github.com/apache/pulsar/pull/18340#discussion_r1014954124


##########
managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/ManagedCursorImpl.java:
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@@ -2707,6 +2707,25 @@ public void operationFailed(ManagedLedgerException exception) {
         });
     }
 
+    /**
+     * Try set {@link #state} to {@link State#Closing}.
+     * @return false if the {@link #state} already is {@link State#Closing} or {@link State#Closed}.
+     */
+    private boolean trySetStateToClosing() {
+        final AtomicBoolean notClosing = new AtomicBoolean(false);
+        STATE_UPDATER.updateAndGet(this, state -> {
+            switch (state){
+                case Closing:
+                case Closed: return state;
+                default: {
+                    notClosing.set(true);
+                    return State.Closing;
+                }

Review Comment:
   [`updateAndGet` doc](https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/atomic/AtomicReferenceFieldUpdater.html#updateAndGet-T-java.util.function.UnaryOperator-) says:
   
   > The function should be side-effect-free, since it may be re-applied when attempted updates fail due to contention among threads.
   
   So I guess `notClosing.set(true)` may cause tricky bugs. How about just 
    comparing the state that before and after `updateAndGet`?



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