[GitHub] [flink] tillrohrmann commented on a change in pull request #14963: [FLINK-21362][coordination] Move State.onEnter() logic into constructor
tillrohrmann commented on a change in pull request #14963:
URL: https://github.com/apache/flink/pull/14963#discussion_r579203833
##
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();
-}
+ void transitionToState(StateFactory 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 we could even make it a bit more explicit by having a dedicated
flag which we check before doing the state transition. That way the program
would directly fail when a new state transition is triggered and not later when
the outer state transition will be continued.
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[GitHub] [flink] tillrohrmann commented on a change in pull request #14963: [FLINK-21362][coordination] Move State.onEnter() logic into constructor
tillrohrmann commented on a change in pull request #14963:
URL: https://github.com/apache/flink/pull/14963#discussion_r579106103
##
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();
-}
+ void transitionToState(StateFactory targetState) {
Review comment:
Can't `S extends State` be part of the `StateFactory`?
##
File path:
flink-runtime/src/main/java/org/apache/flink/runtime/scheduler/declarative/StateFactory.java
##
@@ -0,0 +1,30 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ *http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.runtime.scheduler.declarative;
+
+/**
+ * Factory for creating state instances.
+ *
+ * @param Type of the state.
+ */
+public interface StateFactory {
Review comment:
Should we limit `T extends State`?
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[GitHub] [flink] tillrohrmann commented on a change in pull request #14963: [FLINK-21362][coordination] Move State.onEnter() logic into constructor
tillrohrmann commented on a change in pull request #14963:
URL: https://github.com/apache/flink/pull/14963#discussion_r579105092
##
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();
-}
+ void transitionToState(StateFactory 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:
Theoretically, we could remember in the `transitionToState` method
whether we are currently doing a state transition. If this is the case, then we
enqueue the `targetState` in some queue. If not, then we set the flag that we
are transitioning into a new state and do the state transition. Once we are
complete with a state transition we check the queue for enqueued state
transitions. Only if all state transitions are dequeued, we switch the flag
back to not doing a state transition.
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