Replace AtomicLong to long while ReentrantReadWriteLock is enough (#3)

* Replace AtomicLong to long while ReentrantReadWriteLock is enough

* replace ReentrantReadWriteLock to StampedLock

* unlockWrite

jraft-core/src/main/java/com/alipay/sofa/jraft/core/BallotBox.java

@@ -16,10 +16,7 @@
  */
 package com.alipay.sofa.jraft.core;
 
-import java.util.concurrent.atomic.AtomicLong;
-import java.util.concurrent.locks.Lock;
-import java.util.concurrent.locks.ReadWriteLock;
-import java.util.concurrent.locks.ReentrantReadWriteLock;
+import java.util.concurrent.locks.StampedLock;
 
 import javax.annotation.concurrent.ThreadSafe;
 
@@ -51,10 +48,8 @@ public class BallotBox implements Lifecycle<BallotBoxOptions> {
 
     private FSMCaller                  waiter;
     private ClosureQueue               closureQueue;
-    private final ReadWriteLock        lock               = new ReentrantReadWriteLock();
-    private final Lock                 readLock           = lock.readLock();
-    private final Lock                 writeLock          = lock.writeLock();
-    private final AtomicLong           lastCommittedIndex = new AtomicLong(0);
+    private final StampedLock          stampedLock        = new StampedLock();
+    private long                       lastCommittedIndex =  0;
     private long                       pendingIndex;
     private final ArrayDequeue<Ballot> pendingMetaQueue   = new ArrayDequeue<>();
 
@@ -69,11 +64,16 @@ ArrayDequeue<Ballot> getPendingMetaQueue() {
     }
 
     public long getLastCommittedIndex() {
-        readLock.lock();
+        long stamp = stampedLock.tryOptimisticRead();
+        long optimisticVal = this.lastCommittedIndex;
+        if (stampedLock.validate(stamp)) {
+            return optimisticVal;
+        }
+        stamp = stampedLock.readLock();
         try {
-            return this.lastCommittedIndex.get();
+            return this.lastCommittedIndex;
         } finally {
-            readLock.unlock();
+            stampedLock.unlockRead(stamp);
         }
     }
 
@@ -94,7 +94,7 @@ public boolean init(BallotBoxOptions opts) {
      */
     public boolean commitAt(long firstLogIndex, long lastLogIndex, PeerId peer) {
         //TODO  use lock-free algorithm here?
-        writeLock.lock();
+        final long stamp = stampedLock.writeLock();
         long lastCommittedIndex = 0;
         try {
             if (pendingIndex == 0) {
@@ -131,9 +131,9 @@ public boolean commitAt(long firstLogIndex, long lastLogIndex, PeerId peer) {
                 LOG.debug("Committed log index={}", index);
             }
             pendingIndex = lastCommittedIndex + 1;
-            this.lastCommittedIndex.set(lastCommittedIndex);
+            this.lastCommittedIndex = lastCommittedIndex;
         } finally {
-            writeLock.unlock();
+            stampedLock.unlockWrite(stamp);
         }
         this.waiter.onCommitted(lastCommittedIndex);
         return true;
@@ -146,13 +146,13 @@ public boolean commitAt(long firstLogIndex, long lastLogIndex, PeerId peer) {
      * truncate.
      */
     public void clearPendingTasks() {
-        writeLock.lock();
+        final long stamp = stampedLock.writeLock();
         try {
             this.pendingMetaQueue.clear();
             this.pendingIndex = 0;
             this.closureQueue.clear();
         } finally {
-            writeLock.unlock();
+            stampedLock.unlockWrite(stamp);
         }
     }
 
@@ -166,23 +166,23 @@ public void clearPendingTasks() {
      * @return returns true if reset success
      */
     public boolean resetPendingIndex(long newPendingIndex) {
-        writeLock.lock();
+        final long stamp = stampedLock.writeLock();
         try {
             if (!(pendingIndex == 0 && pendingMetaQueue.isEmpty())) {
                 LOG.error("resetPendingIndex fail, pendingIndex={}, pendingMetaQueueSize={}", pendingIndex,
                     pendingMetaQueue.size());
                 return false;
             }
-            if (newPendingIndex <= this.lastCommittedIndex.get()) {
+            if (newPendingIndex <= this.lastCommittedIndex) {
                 LOG.error("resetPendingIndex fail, newPendingIndex={}, lastCommittedIndex={}", newPendingIndex,
-                    lastCommittedIndex.get());
+                    lastCommittedIndex);
                 return false;
             }
             this.pendingIndex = newPendingIndex;
             this.closureQueue.resetFirstIndex(newPendingIndex);
             return true;
         } finally {
-            writeLock.unlock();
+            stampedLock.unlockWrite(stamp);
         }
     }
 
@@ -201,7 +201,7 @@ public boolean appendPendingTask(Configuration conf, Configuration oldConf, Clos
             LOG.error("Fail to init ballot");
             return false;
         }
-        writeLock.lock();
+        final long stamp = stampedLock.writeLock();
         try {
             if (pendingIndex <= 0) {
                 LOG.error("Fail to appendingTask, pendingIndex={}", pendingIndex);
@@ -211,7 +211,7 @@ public boolean appendPendingTask(Configuration conf, Configuration oldConf, Clos
             this.closureQueue.appendPendingClosure(done);
             return true;
         } finally {
-            writeLock.unlock();
+            stampedLock.unlockWrite(stamp);
         }
     }
 
@@ -223,26 +223,26 @@ public boolean appendPendingTask(Configuration conf, Configuration oldConf, Clos
      */
     public boolean setLastCommittedIndex(long lastCommittedIndex) {
         boolean doUnlock = true;
-        writeLock.lock();
+        final long stamp = stampedLock.writeLock();
         try {
             if (pendingIndex != 0 || !pendingMetaQueue.isEmpty()) {
                 Requires.requireTrue(lastCommittedIndex < this.pendingIndex,
                     "Node changes to leader, pendingIndex=%d, param lastCommittedIndex=%d",
                     pendingIndex,lastCommittedIndex);
                 return false;
             }
-            if (lastCommittedIndex < this.lastCommittedIndex.get()) {
+            if (lastCommittedIndex < this.lastCommittedIndex) {
                 return false;
             }
-            if (lastCommittedIndex > this.lastCommittedIndex.get()) {
-                this.lastCommittedIndex.set(lastCommittedIndex);
-                writeLock.unlock();
+            if (lastCommittedIndex > this.lastCommittedIndex) {
+                this.lastCommittedIndex = lastCommittedIndex;
+                stampedLock.unlockWrite(stamp);
                 doUnlock = false;
                 this.waiter.onCommitted(lastCommittedIndex);
             }
         } finally {
             if (doUnlock) {
-                writeLock.unlock();
+                stampedLock.unlockWrite(stamp);
             }
         }
         return true;