zhuzhurk commented on a change in pull request #9663: 
[WIP][FLINK-12433][runtime] Implement DefaultScheduler stub
URL: https://github.com/apache/flink/pull/9663#discussion_r326899233
 
 

 ##########
 File path: 
flink-runtime/src/main/java/org/apache/flink/runtime/scheduler/DefaultScheduler.java
 ##########
 @@ -75,10 +137,281 @@ public DefaultScheduler(
                        slotRequestTimeout,
                        shuffleMaster,
                        partitionTracker);
+
+               this.restartBackoffTimeStrategy = restartBackoffTimeStrategy;
+               this.slotRequestTimeout = slotRequestTimeout;
+               this.slotProvider = slotProvider;
+               this.delayExecutor = delayExecutor;
+               this.userCodeLoader = userCodeLoader;
+               this.schedulingStrategyFactory = 
checkNotNull(schedulingStrategyFactory);
+               this.failoverStrategyFactory = 
checkNotNull(failoverStrategyFactory);
+               this.executionVertexOperations = 
checkNotNull(executionVertexOperations);
+               this.executionVertexVersioner = executionVertexVersioner;
+               this.conditionalFutureHandlerFactory = new 
ConditionalFutureHandlerFactory(executionVertexVersioner);
+       }
+
+       // 
------------------------------------------------------------------------
+       // SchedulerNG
+       // 
------------------------------------------------------------------------
+
+       @Override
+       public void startSchedulingInternal() {
+               initializeScheduling();
+               schedulingStrategy.startScheduling();
+       }
+
+       private void initializeScheduling() {
+               executionFailureHandler = new 
ExecutionFailureHandler(failoverStrategyFactory.create(getFailoverTopology()), 
restartBackoffTimeStrategy);
+               schedulingStrategy = 
schedulingStrategyFactory.createInstance(this, getSchedulingTopology(), 
getJobGraph());
+               executionSlotAllocator = new 
DefaultExecutionSlotAllocator(slotProvider, getInputsLocationsRetriever(), 
slotRequestTimeout);
+               setTaskFailureListener(new 
UpdateTaskExecutionStateInDefaultSchedulerListener(this, 
getJobGraph().getJobID()));
+               prepareExecutionGraphForScheduling();
+       }
+
+       @Override
+       public boolean updateTaskExecutionState(final TaskExecutionState 
taskExecutionState) {
+               final Optional<ExecutionVertexID> executionVertexIdOptional = 
getExecutionVertexId(taskExecutionState.getID());
+               if (executionVertexIdOptional.isPresent()) {
+                       final ExecutionVertexID executionVertexId = 
executionVertexIdOptional.get();
+                       updateState(taskExecutionState);
+                       
schedulingStrategy.onExecutionStateChange(executionVertexId, 
taskExecutionState.getExecutionState());
+                       maybeHandleTaskFailure(taskExecutionState, 
executionVertexId);
 
 Review comment:
   I think the potential that `schedulingStrategy.onExecutionStateChange` 
changes task state directly in this thread is not good:
    * It can cause call stack chain that is hard to imagine, which makes it 
hard to maintain
    * a very long call stack chain may result in stack overflow
    * when we invoke `maybeHandleTaskFailure` right after invoking 
`schedulingStrategy.onExecutionStateChange`, the task state may even have 
changed in the call stack chain so that we are doing failover handling in an 
unexpected state
   
   How about to define that `SchedulerOperations#allocateSlotsAndDeploy` does 
not take effect in the direct invoking? And then change the actions in 
`allocateSlotsAndDeploy` to be executed in the main thread.
   In this way we can have the assumption that no task state change happens 
when invoking `schedulingStrategy.onExecutionStateChange` here.

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