[GitHub] [ozone] siddhantsangwan commented on a diff in pull request #3738: HDDS-7204. EC: Schedule UnderReplicatedProcessor and OverReplicatedProcessor threads in RM instead of StorageContainerManager

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

siddhantsangwan commented on code in PR #3738:
URL: https://github.com/apache/ozone/pull/3738#discussion_r964660812


##########
hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/container/replication/ReplicationManager.java:
##########
@@ -248,6 +261,38 @@ public synchronized void stop() {
     }
   }
 
+  /**
+   * Create Replication Manager sub services such as Over and Under Replication
+   * processors.
+   */
+  private void createSubServices() {

Review Comment:
   > I thought we concluded that these sub-services should not be registered with the ServiceManager themselves, but just be threads managed within the replication manager?
   
   Yeah. When implementing that, I realised that we would end up writing code similar to BackgroundSCMService. `BackgroundThread` implementing Runnable will have something like:
   ```
     private void run() {
       while (running.get()) {
         try {
           if (shouldRun()) {
             try {
               periodicalTask.run();
             } catch (Throwable e) {
               log.error("Caught Unhandled exception in {}. The task will be " +
                   "re-tried in {}ms", getServiceName(), intervalInMillis, e);
             }
           }
           synchronized (this) {
             if (!runImmediately) {
               wait(intervalInMillis);
             }
             runImmediately = false;
           }
         } catch (InterruptedException e) {
           log.warn("{} is interrupted, exit", serviceName);
           Thread.currentThread().interrupt();
           running.set(false);
         }
       }
     }
   ```
   We can avoid doing this by using BackgroundSCMService. The downside is that our definition of whether they are RM sub threads or SCM threads becomes hazy. But we are solving a part of that problem by restricting their visibility to only RM and SCMServiceManager. 



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