[GitHub] [rocketmq] yuyijq opened a new issue #1101: 改进GroupCommitService里锁的可理解性

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

yuyijq opened a new issue #1101: 改进GroupCommitService里锁的可理解性
URL: https://github.com/apache/rocketmq/issues/1101
 
 
   GroupCommitService(at CommitLog)里使用了好几个锁，并且有两个地方在可变变量上加锁，花了较长时间才弄明白这几个锁的真实目的，是不是可以将锁改成下面的形式，除了提高可理解性外，也不会出现sonar warning，这样改了之后性能也没有什么降低：
   ```java
       class GroupCommitService extends FlushCommitLogService {
           private volatile List<GroupCommitRequest> requestsWrite = new ArrayList<GroupCommitRequest>();
           private volatile List<GroupCommitRequest> requestsRead = new ArrayList<GroupCommitRequest>();
   
           public synchronized void putRequest(final GroupCommitRequest request) {
              //去掉对requestsWrite的加锁
               this.requestsWrite.add(request);
               if (hasNotified.compareAndSet(false, true)) {
                   waitPoint.countDown(); // notify
               }
           }
   
          //在这里增加方法同步块
           private synchronized void swapRequests() {
               List<GroupCommitRequest> tmp = this.requestsWrite;
               this.requestsWrite = this.requestsRead;
               this.requestsRead = tmp;
           }
   
           private void doCommit() {
                   //去掉对requestsRead加锁
                   if (!this.requestsRead.isEmpty()) {
                       for (GroupCommitRequest req : this.requestsRead) {
                           // There may be a message in the next file, so a maximum of
                           // two times the flush
                           boolean flushOK = false;
                           for (int i = 0; i < 2 && !flushOK; i++) {
                               flushOK = CommitLog.this.mappedFileQueue.getFlushedWhere() >= req.getNextOffset();
   
                               if (!flushOK) {
                                   CommitLog.this.mappedFileQueue.flush(0);
                               }
                           }
   
                           req.wakeupCustomer(flushOK);
                       }
   
                       long storeTimestamp = CommitLog.this.mappedFileQueue.getStoreTimestamp();
                       if (storeTimestamp > 0) {
                           CommitLog.this.defaultMessageStore.getStoreCheckpoint().setPhysicMsgTimestamp(storeTimestamp);
                       }
   
                       this.requestsRead.clear();
                   } else {
                       // Because of individual messages is set to not sync flush, it
                       // will come to this process
                       CommitLog.this.mappedFileQueue.flush(0);
                   }
           }
   
           public void run() {
               CommitLog.log.info(this.getServiceName() + " service started");
   
               while (!this.isStopped()) {
                   try {
                       this.waitForRunning(10);
                       this.doCommit();
                   } catch (Exception e) {
                       CommitLog.log.warn(this.getServiceName() + " service has exception. ", e);
                   }
               }
   
               // Under normal circumstances shutdown, wait for the arrival of the
               // request, and then flush
               try {
                   Thread.sleep(10);
               } catch (InterruptedException e) {
                   CommitLog.log.warn("GroupCommitService Exception, ", e);
               }
              this.swapRequests();
              this.doCommit();
               CommitLog.log.info(this.getServiceName() + " service end");
           }
   
           @Override
           protected void onWaitEnd() {
               this.swapRequests();
           }
       }
   ```

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