rmetzger commented on a change in pull request #14963:
URL: https://github.com/apache/flink/pull/14963#discussion_r578983459
##########
File path:
flink-runtime/src/main/java/org/apache/flink/runtime/scheduler/declarative/DeclarativeScheduler.java
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@@ -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:
It would probably work with the tests, since we collect and manually
trigger all scheduled executions in the close() method, before checking if the
expected state transitions happened.
But I'm not sure if it's worth introducing such behavior for the sake of
removing the onEnter() method.
One of the reasons why we agreed to remove onEnter() was because the change
revealed a few test inaccuracies. Basically all of these inaccuracies have been
found and fixed during the review of the respective tests. The onEnter()
prototype was just done on an unreviewed version of the tests.
Right now, WaitingForResources is the only state that triggers state
transitions in the constructor.
I would actually propose to revisit the decision to remove the onEnter()
method, given the compromises we have to do to make it work (CC @tillrohrmann )
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