zentol commented on a change in pull request #14963:
URL: https://github.com/apache/flink/pull/14963#discussion_r579316566
##########
File path:
flink-runtime/src/main/java/org/apache/flink/runtime/scheduler/declarative/DeclarativeScheduler.java
##########
@@ -907,20 +909,37 @@ public void runIfState(State expectedState, Runnable
action, Duration delay) {
// ----------------------------------------------------------------
+ /** Note: Do not call this method from a State constructor. */
@VisibleForTesting
- void transitionToState(State newState) {
- if (state != newState) {
- LOG.debug(
- "Transition from state {} to {}.",
- state.getClass().getSimpleName(),
- newState.getClass().getSimpleName());
-
- State oldState = state;
- oldState.onLeave(newState.getClass());
-
- state = newState;
- newState.onEnter();
- }
+ <S extends State> void transitionToState(StateFactory<S> targetState) {
+ Preconditions.checkState(
+ state != null, "State transitions are now allowed while
construcing a state.");
+ Preconditions.checkState(
+ state.getClass() != targetState.getStateClass(),
+ "Attempted to transition into the very state the scheduler is
already in.");
+
+ LOG.debug(
+ "Transition from state {} to {}.",
+ state.getClass().getSimpleName(),
+ targetState.getStateClass().getSimpleName());
+
+ State oldState = state;
+ oldState.onLeave(targetState.getStateClass());
+
+ // Guard against state transitions while constructing state objects.
+ //
+ // Consider the following scenario:
+ // Scheduler is in state Restarting, once the cancellation is
complete, we enter the
+ // transitionToState(WaitingForResources) method.
+ // In the constructor of WaitingForResources, we call
`notifyNewResourcesAvailable()`, which
+ // finds resources and enters transitionsToState(Executing). We are in
state Executing. Then
+ // we return from the methods and go back in our call stack to the
+ // transitionToState(WaitingForResources) call, where we overwrite
Executing with
+ // WaitingForResources. And there we have it, a deployed execution
graph, and a scheduler
+ // that is in WaitingForResources.
+ state = null;
Review comment:
maybe a flag is easier to read though
```
this.isTransitioningState = true
this.state.onLeave()
this.state = targetState.getState()
this.state = onEnter()
this.isTransitioningState = false; // maybe this should be done in a finally
block...what actually happens if a transition throws an exception?
```
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