Tasks scheduled through 'SchedulerBinding.instance.scheduleTask' were not executed #82016
Description
Issue
I start the animation during initialization and then execute the task . After the animation ends, the task is not executed.
@override
void initState() {
super.initState();
animationController = AnimationController(
vsync: this, duration: Duration(milliseconds: 3000));
animation = Tween(begin: 1.0, end: 0.0).animate(animationController);
// start an animation
animationController.forward();
// These task will be blocked even if the animation ends
SchedulerBinding.instance!.scheduleTask(task1, Priority.idle);
SchedulerBinding.instance!.scheduleTask(task2, Priority.idle);
}Expected results:
Task1 and Task2 are executed after the animation ends
Actual results:
After the animation ends, the task is not executed.
My point of view:
I notice that task1 and task2 are added to _taskQueue for scheduling here
flutter/packages/flutter/lib/src/scheduler/binding.dart
Lines 427 to 441 in 3ab799b
The problem is that once the handleEventLoopCallback() returns false, the _TaskQueue will not be scheduled again until the next scheduleTask.
In this case, because the Priority of the two tasks is Priority.idle, the schedulingStrategy returns false
flutter/packages/flutter/lib/src/scheduler/binding.dart
Lines 455 to 463 in 3ab799b
So task1 and task2 are still blocked after the animation ends
I try to modify these method like this ：
void _ensureEventLoopCallback() {
assert(!locked);
assert(_taskQueue.isNotEmpty);
if (_hasRequestedAnEventLoopCallback)
return;
_hasRequestedAnEventLoopCallback = true;
print('_ensureEventLoopCallback execute');
Timer.run(_runTasks);
}
// Scheduled by _ensureEventLoopCallback.
void _runTasks() {
_hasRequestedAnEventLoopCallback = false;
if (handleEventLoopCallback())
_ensureEventLoopCallback();
else{
// When the execution fails, determines if the queue is empty
if(_taskQueue.isNotEmpty){
// When the task queue is not empty, the judgment is made again
_ensureEventLoopCallback();
}
} // runs next task when there's time
}When the task queue is not empty, the judgment is made again, just like Event loop
In the above example, tasks 1 and 2 were successfully executed after the animation ended
However, through logging, I found that _ensureEventLoopCallback() was called too frequently. Because the Timer.run will continue to add tasks to the isolate while the _taskQueue is not empty
However, I don't think this is necessary, because the result of the schedulingStrategy will not change until the next frame is drawn
So i modify _ensureEventLoopCallback() like this：
// Ensures that the scheduler services a task scheduled by [scheduleTask].
void _ensureEventLoopCallback() async{
assert(!locked);
assert(_taskQueue.isNotEmpty);
if (_hasRequestedAnEventLoopCallback)
return;
_hasRequestedAnEventLoopCallback = true;
print('_ensureEventLoopCallback execute');
// Executes after each frame is rendered
await endOfFrame;
_runTasks();
}At the end of each frame, the _taskQueue is scheduled .
And tasks 1 and 2 were also successfully executed after the animation ended
What do you think, if this change is necessary, I can PR to fix it
[✓] Flutter (Channel stable, 2.0.6, on macOS 11.2.2 20D80 darwin-x64, locale zh-Hans-CN)
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