[GitHub] [zookeeper] BELUGABEHR commented on a change in pull request #870: ZOOKEEPER-3335: Prefer ArrayList over LinkedList

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BELUGABEHR commented on a change in pull request #870: ZOOKEEPER-3335: Prefer ArrayList over LinkedList
URL: https://github.com/apache/zookeeper/pull/870#discussion_r269380411
 
 

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 File path: zookeeper-server/src/main/java/org/apache/zookeeper/server/ZKDatabase.java
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 @@ -187,18 +190,21 @@ public ReentrantReadWriteLock getLogLock() {
     }
 
 
-    public synchronized List<Proposal> getCommittedLog() {
+    public synchronized Collection<Proposal> getCommittedLog() {
+        final Collection<Proposal> result;
         ReadLock rl = logLock.readLock();
-        // only make a copy if this thread isn't already holding a lock
-        if(logLock.getReadHoldCount() <=0) {
+        // make a copy if this thread is not already holding a lock
+        if (logLock.getReadHoldCount() > 0) {
+          result = this.committedLog;
+        } else {
+            rl.lock();
             try {
-                rl.lock();
-                return new LinkedList<Proposal>(this.committedLog);
+                result = new ArrayList<>(this.committedLog);
             } finally {
                 rl.unlock();
             }
         }
-        return this.committedLog;
+        return Collections.unmodifiableCollection(result);
 
 Review comment:
   Thanks @enixon !
   
   In one case, the caller is getting a point-in-time copy of the committedLog queue, and in the other case, the caller is getting the real thing.  That's already a bit unexpected, but I figured at the very least, the caller should not be allowed to modify the real thing outside the scope of this class.

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