1996fanrui commented on code in PR #21923:
URL: https://github.com/apache/flink/pull/21923#discussion_r1114369247


##########
flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/StreamTask.java:
##########
@@ -256,19 +259,27 @@
     private final StreamTaskAsyncExceptionHandler asyncExceptionHandler;
 
     /**
-     * Flag to mark the task "in operation", in which case check needs to be 
initialized to true, so
-     * that early cancel() before invoke() behaves correctly.
+     * INITIALIZED: task constructor was called or on init state. RUNNING: 
task is in operation.
+     * FAILING: task is failing e.g., if an exception has occurred inside 
{@link #invoke()}.
+     * CANCELED: when this task is canceled. FINISHED: task successfully 
terminated.
      */
-    private volatile boolean isRunning;
+    private enum TaskState {
+        FINISHED(Arrays.asList(new TaskState[] {})),
+        CANCELED(Arrays.asList(new TaskState[] {})),
+        RUNNING(Arrays.asList(new TaskState[] {CANCELED, FINISHED})),
+        INITIALIZED(Arrays.asList(new TaskState[] {RUNNING, CANCELED, 
FINISHED}));
 
-    /** Flag to mark this task as canceled. */
-    private volatile boolean canceled;
+        private List<TaskState> validFromStates;
+        private boolean failing = false;

Review Comment:
   Why add the `failing` inside the `TaskState`?



##########
flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/StreamTask.java:
##########
@@ -256,19 +259,27 @@
     private final StreamTaskAsyncExceptionHandler asyncExceptionHandler;
 
     /**
-     * Flag to mark the task "in operation", in which case check needs to be 
initialized to true, so
-     * that early cancel() before invoke() behaves correctly.
+     * INITIALIZED: task constructor was called or on init state. RUNNING: 
task is in operation.
+     * FAILING: task is failing e.g., if an exception has occurred inside 
{@link #invoke()}.
+     * CANCELED: when this task is canceled. FINISHED: task successfully 
terminated.

Review Comment:
   How about drawing a state transition diagram? Similar to ExecutionState's 
annotation[1], it will be clearer.
   
   [1] 
https://github.com/apache/flink/blob/2e91543836d667a0b367688bb5ce290c3164479c/flink-runtime/src/main/java/org/apache/flink/runtime/execution/ExecutionState.java#L26
   
   



##########
flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/StreamTask.java:
##########
@@ -256,19 +259,27 @@
     private final StreamTaskAsyncExceptionHandler asyncExceptionHandler;
 
     /**
-     * Flag to mark the task "in operation", in which case check needs to be 
initialized to true, so
-     * that early cancel() before invoke() behaves correctly.
+     * INITIALIZED: task constructor was called or on init state. RUNNING: 
task is in operation.
+     * FAILING: task is failing e.g., if an exception has occurred inside 
{@link #invoke()}.
+     * CANCELED: when this task is canceled. FINISHED: task successfully 
terminated.
      */
-    private volatile boolean isRunning;
+    private enum TaskState {
+        FINISHED(Arrays.asList(new TaskState[] {})),
+        CANCELED(Arrays.asList(new TaskState[] {})),
+        RUNNING(Arrays.asList(new TaskState[] {CANCELED, FINISHED})),
+        INITIALIZED(Arrays.asList(new TaskState[] {RUNNING, CANCELED, 
FINISHED}));
 
-    /** Flag to mark this task as canceled. */
-    private volatile boolean canceled;
+        private List<TaskState> validFromStates;
+        private boolean failing = false;
 
-    /**
-     * Flag to mark this task as failing, i.e. if an exception has occurred 
inside {@link
-     * #invoke()}.
-     */
-    private volatile boolean failing;
+        TaskState(List<TaskState> validFromStates) {
+            this.validFromStates = validFromStates;
+        }
+
+        public boolean isValidTransition(TaskState fromState, TaskState 
toState) {

Review Comment:
   The method isn't called, right?
   
   As I understand, it should be called when transition state, right?



##########
flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/StreamTask.java:
##########
@@ -256,19 +259,27 @@
     private final StreamTaskAsyncExceptionHandler asyncExceptionHandler;
 
     /**
-     * Flag to mark the task "in operation", in which case check needs to be 
initialized to true, so
-     * that early cancel() before invoke() behaves correctly.
+     * INITIALIZED: task constructor was called or on init state. RUNNING: 
task is in operation.

Review Comment:
   How about moving the description of the state to the corresponding state 
field? It's similar to `JobStatus`[1] or `ExecutionState`[2].
   
   [1] 
https://github.com/apache/flink/blob/2e91543836d667a0b367688bb5ce290c3164479c/flink-core/src/main/java/org/apache/flink/api/common/JobStatus.java#L26
   [2] 
https://github.com/apache/flink/blob/2e91543836d667a0b367688bb5ce290c3164479c/flink-runtime/src/main/java/org/apache/flink/runtime/execution/ExecutionState.java#L57
   
   



##########
flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/StreamTask.java:
##########
@@ -256,19 +259,27 @@
     private final StreamTaskAsyncExceptionHandler asyncExceptionHandler;
 
     /**
-     * Flag to mark the task "in operation", in which case check needs to be 
initialized to true, so
-     * that early cancel() before invoke() behaves correctly.
+     * INITIALIZED: task constructor was called or on init state. RUNNING: 
task is in operation.
+     * FAILING: task is failing e.g., if an exception has occurred inside 
{@link #invoke()}.
+     * CANCELED: when this task is canceled. FINISHED: task successfully 
terminated.
      */
-    private volatile boolean isRunning;
+    private enum TaskState {
+        FINISHED(Arrays.asList(new TaskState[] {})),
+        CANCELED(Arrays.asList(new TaskState[] {})),
+        RUNNING(Arrays.asList(new TaskState[] {CANCELED, FINISHED})),
+        INITIALIZED(Arrays.asList(new TaskState[] {RUNNING, CANCELED, 
FINISHED}));
 
-    /** Flag to mark this task as canceled. */
-    private volatile boolean canceled;
+        private List<TaskState> validFromStates;

Review Comment:
   How about using `Set` instead of `List` due to we always call 
`validFromStates.contains()`?



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