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Merge pull request #74 from Workiva/DOCPLAT-1525
DOCPLAT-1525 Create least recently used caching strategy
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,61 @@ | ||
| import 'dart:async'; | ||
| import 'dart:collection'; | ||
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| import 'package:w_common/cache.dart'; | ||
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| /// A [CachingStrategy] that will hold the last n most recently used [TValue]s. | ||
| /// | ||
| /// When n = 0 the strategy will remove a [TIdentifier] [TValue] pair immediately | ||
| /// on release. | ||
| class LeastRecentlyUsedStrategy<TIdentifier, TValue> | ||
| extends CachingStrategy<TIdentifier, TValue> { | ||
| /// [TIdentifier]s that have been released but not yet removed in order of most | ||
| /// to least recently used. | ||
| final Queue<TIdentifier> _removalQueue = new Queue<TIdentifier>(); | ||
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| /// The number of recently used [TIdentifier] [TValue] pairs to keep in the | ||
| /// cache before removing the least recently used pair from the cache. | ||
| final int _keep; | ||
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| LeastRecentlyUsedStrategy(this._keep) { | ||
| if (_keep < 0) { | ||
| throw new ArgumentError( | ||
| 'Cannot keep a negative number of most recently used items in the cache'); | ||
| } | ||
| } | ||
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| @override | ||
| Future<Null> onDidRelease( | ||
| TIdentifier id, TValue value, Future<Null> remove(TIdentifier id)) async { | ||
| // If there are more than _keep items in the queue remove the least recently | ||
| // used. | ||
| while (_removalQueue.length > _keep) { | ||
| await remove(_removalQueue.removeLast()); | ||
| } | ||
| } | ||
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| @override | ||
| void onWillGet(TIdentifier id) { | ||
| // A get has been called for id, removing it is now unnecessary. | ||
| _removalQueue.remove(id); | ||
| } | ||
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| @override | ||
| void onWillRelease(TIdentifier id) { | ||
| // id has been released, add it to the front of the removal queue. If | ||
| // necessary, the least recently used items will be removed in onDidRemove | ||
| // which the cache will call after any pending async value factory | ||
| // associated with id completes. Items are added to the removal queue in | ||
| // onWillRelease rather than onDidRelease to allow a get called before an | ||
| // async value factory completes to cancel an unnecessary removal. | ||
| if (!_removalQueue.contains(id)) { | ||
| _removalQueue.addFirst(id); | ||
| } | ||
| } | ||
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| @override | ||
| void onWillRemove(TIdentifier id) { | ||
| // id will be removed, removing it again is unnecessary. | ||
| _removalQueue.remove(id); | ||
| } | ||
| } |
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71 changes: 71 additions & 0 deletions
71
test/unit/browser/cache/least_recently_used_strategy_test.dart
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,71 @@ | ||
| import 'dart:async'; | ||
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| import 'package:test/test.dart'; | ||
| import 'package:w_common/src/common/cache/cache.dart'; | ||
| import 'package:w_common/src/common/cache/least_recently_used_strategy.dart'; | ||
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| void main() { | ||
| group('MostRecentlyUsedStrategy', () { | ||
| var expectedId = 'expectedId'; | ||
| var expectedValue = 'expectedValue'; | ||
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| for (var i in new Iterable<int>.generate(3)) { | ||
| Cache<String, Object> cache; | ||
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| setUp(() async { | ||
| cache = new Cache<String, Object>(new LeastRecentlyUsedStrategy(i)); | ||
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| // install expected item | ||
| await cache.get(expectedId, () => expectedValue); | ||
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| // install i items into cache | ||
| for (var j in new Iterable<int>.generate(i)) { | ||
| await cache.get('$j', () => j); | ||
| } | ||
| }); | ||
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| test( | ||
| 'release should remove released item after $i additional releases ' | ||
| 'when storing $i most recently used items', () async { | ||
| cache.didRemove.listen(expectAsync1((context) { | ||
| expect(context.id, expectedId); | ||
| expect(context.value, expectedValue); | ||
| })); | ||
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| // release expected item | ||
| await cache.release(expectedId); | ||
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| // create i releases, after which expected item (and only expected | ||
| // item) should be released | ||
| for (var j in new Iterable<int>.generate(i)) { | ||
| await cache.release('$j'); | ||
| } | ||
| }); | ||
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| test( | ||
| 'release after a synchronous getAsync remove getAsync call should ' | ||
| 'remove released item after $i additional releases when storing $i ' | ||
| 'most recently used items', () async { | ||
| cache.didRemove.listen(expectAsync1((context) { | ||
| expect(context.id, expectedId); | ||
| expect(context.value, expectedValue); | ||
| }, count: 2)); | ||
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| var firstGet = cache.getAsync(expectedId, () async => expectedValue); | ||
| var remove = cache.remove(expectedId); | ||
| var secondGet = cache.getAsync(expectedId, () async => expectedValue); | ||
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| // release expected item | ||
| var release = cache.release(expectedId); | ||
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| await Future.wait([firstGet, remove, secondGet, release]); | ||
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| // create i releases, after which expected item (and only expected | ||
| // item) should be released | ||
| for (var j in new Iterable<int>.generate(i)) { | ||
| await cache.release('$j'); | ||
| } | ||
| }); | ||
| } | ||
| }); | ||
| } |
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