[GitHub] [rocketmq] XiaoyiPeng commented on a change in pull request #3509: [ISSUE #2516]: Fix the value of sendThreadPoolQueueHeadWaitTimeMills is 0 most of the time

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

XiaoyiPeng commented on a change in pull request #3509:
URL: https://github.com/apache/rocketmq/pull/3509#discussion_r752836279



##########
File path: broker/src/main/java/org/apache/rocketmq/broker/BrokerController.java
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@@ -650,10 +652,13 @@ public void protectBroker() {
 
     public long headSlowTimeMills(BlockingQueue<Runnable> q) {
         long slowTimeMills = 0;
-        final Runnable peek = q.peek();
-        if (peek != null) {
-            RequestTask rt = BrokerFastFailure.castRunnable(peek);
-            slowTimeMills = rt == null ? 0 : this.messageStore.now() - rt.getCreateTimestamp();
+        Optional<RequestTask> op = q.stream()

Review comment:
       Thanks for your review.
   
   It has nothing to do with thread safety, There is to reduce thread contention, `q` is polled by thread in `BrokerController#sendMessageExecutor` and will be peeked by thread in `BrokerController#scheduledExecutorService`  per second as shown below:
   
   ```
   this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {
                   @Override
                   public void run() {
                       try {
                           BrokerController.this.printWaterMark();
                       } catch (Throwable e) {
                           log.error("printWaterMark error.", e);
                       }
                   }
               }, 10, 1, TimeUnit.SECONDS);
   ```
   You can look at the issue #2516 , get some context info first.




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