Fix concurrency issues in tool execution #2730
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I love this, but I'd love a review from @jcollins-g as well before we merge.
| class MultiFutureTracker<T> { | ||
| /// Approximate maximum number of simultaneous active Futures. | ||
| final int parallel; | ||
| typedef TaskQueueClosure<T> = Future<T> Function(); |
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Oh, this makes things so much easier to read.
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| final Queue<_TaskQueueItem<T>> _pendingTasks = Queue<_TaskQueueItem<T>>(); | ||
| final Set<_TaskQueueItem<T>> _activeTasks = <_TaskQueueItem<T>>{}; | ||
| final Set<Completer<void>> _completeListeners = <Completer<void>>{}; |
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yes, this structure is more easily verified than the queue-length original version for waiting on completion. nice.
lib/src/io_utils.dart
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| Future<T> add(TaskQueueClosure<T> task) { | ||
| final completer = Completer<T>(); | ||
| _pendingTasks.add(_TaskQueueItem<T>(task, completer)); | ||
| _processTasks(); |
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IIUC this seems like it will spawn a lot of _processTasks() that could potentially do "duplicate" work in the case where the _processTask() from the onComplete has it covered. This is probably fine though as the duplicates are written to collapse and do nothing. The old version probably got into trouble doing things cleverly to avoid this...
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Yes, possibly, but it would also make sure that when a new task is added, it starts running right away.
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Sure. I was thinking of the case though when the maximum concurrency is reached and _processTasks() here doesn't have any useful effect. It seems like it should be OK just to inline _processTasks() here and eliminate an unawaited future that sometimes doesn't do anything. Your choice, and of course, only if it works just as well.
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Oh, good point, that makes sense. OK, I inlined it.
Description
This replaces the task queue called
MultiFutureTrackerwith aTaskQueue, which fixes the concurrency issue where the old class didn't really wait for tasks to complete before starting a new one.This uses a completer to provide a new future to wait for each task, uses a
Queueto keep the tasks, and returns aFuture<T>with the result of the task instead of waiting on aFuture<void>.There is also a future to wait on that will complete when the queue is empty (replacing
wait) calledtasksComplete.Related Issues
Tests