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1 // Copyright (c) 2012, the Dart project authors. Please see the AUTHORS file | 1 // Copyright (c) 2011, the Dart project authors. Please see the AUTHORS file |
2 // for details. All rights reserved. Use of this source code is governed by a | 2 // for details. All rights reserved. Use of this source code is governed by a |
3 // BSD-style license that can be found in the LICENSE file. | 3 // BSD-style license that can be found in the LICENSE file. |
4 | 4 |
5 bool _inMeasurementFrame = false; | 5 typedef Object ComputeValue(); |
| 6 |
| 7 class _MeasurementRequest<T> { |
| 8 final ComputeValue computeValue; |
| 9 final Completer<T> completer; |
| 10 Object value; |
| 11 bool exception = false; |
| 12 _MeasurementRequest(this.computeValue, this.completer); |
| 13 } |
6 | 14 |
7 final _MEASUREMENT_MESSAGE = "DART-MEASURE"; | 15 final _MEASUREMENT_MESSAGE = "DART-MEASURE"; |
8 | 16 List<_MeasurementRequest> _pendingRequests; |
9 Queue<MeasurementCallback> _pendingMeasurementFrameCallbacks; | 17 List<TimeoutHandler> _pendingMeasurementFrameCallbacks; |
10 bool _nextMeasurementFrameScheduled = false; | 18 bool _nextMeasurementFrameScheduled = false; |
11 bool _firstMeasurementRequest = true; | 19 bool _firstMeasurementRequest = true; |
12 | 20 |
13 void _maybeScheduleMeasurementFrame() { | 21 void _maybeScheduleMeasurementFrame() { |
14 if (_nextMeasurementFrameScheduled) return; | 22 if (_nextMeasurementFrameScheduled) return; |
15 | 23 |
16 _nextMeasurementFrameScheduled = true; | 24 _nextMeasurementFrameScheduled = true; |
17 // postMessage gives us a way to receive a callback after the current | 25 // postMessage gives us a way to receive a callback after the current |
18 // event listener has unwound but before the browser has repainted. | 26 // event listener has unwound but before the browser has repainted. |
19 if (_firstMeasurementRequest) { | 27 if (_firstMeasurementRequest) { |
20 // Messages from other windows do not cause a security risk as | 28 // Messages from other windows do not cause a security risk as |
21 // all we care about is that _onCompleteMeasurementRequests is called | 29 // all we care about is that _onCompleteMeasurementRequests is called |
22 // after the current event loop is unwound and calling | 30 // after the current event loop is unwound and calling the function is |
23 // _runMeasurementFrames is a noop when zero requests are pending. | 31 // a noop when zero requests are pending. |
24 window.on.message.add((e) => _runMeasurementFrames()); | 32 window.on.message.add((e) => _completeMeasurementFutures()); |
25 _firstMeasurementRequest = false; | 33 _firstMeasurementRequest = false; |
26 } | 34 } |
27 | 35 |
28 // TODO(jacobr): other mechanisms such as setImmediate and | 36 // TODO(jacobr): other mechanisms such as setImmediate and |
29 // requestAnimationFrame may work better of platforms that support them. | 37 // requestAnimationFrame may work better of platforms that support them. |
30 // The key is we need a way to execute code immediately after the current | 38 // The key is we need a way to execute code immediately after the current |
31 // event listener queue unwinds. | 39 // event listener queue unwinds. |
32 window.postMessage(_MEASUREMENT_MESSAGE, "*"); | 40 window.postMessage(_MEASUREMENT_MESSAGE, "*"); |
33 } | 41 } |
34 | 42 |
35 /** | 43 /** |
36 * Registers a [callback] which is called after the next batch of measurements | 44 * Registers a [callback] which is called after the next batch of measurements |
37 * completes. Even if no measurements completed, the callback is triggered | 45 * completes. Even if no measurements completed, the callback is triggered |
38 * when they would have completed to avoid confusing bugs if it happened that | 46 * when they would have completed to avoid confusing bugs if it happened that |
39 * no measurements were actually requested. | 47 * no measurements were actually requested. |
40 */ | 48 */ |
41 void _addMeasurementFrameCallback(MeasurementCallback callback) { | 49 void _addMeasurementFrameCallback(TimeoutHandler callback) { |
42 assert(callback != null); | |
43 if (_pendingMeasurementFrameCallbacks === null) { | 50 if (_pendingMeasurementFrameCallbacks === null) { |
44 _pendingMeasurementFrameCallbacks = new Queue<MeasurementCallback>(); | 51 _pendingMeasurementFrameCallbacks = <TimeoutHandler>[]; |
| 52 _maybeScheduleMeasurementFrame(); |
45 } | 53 } |
46 _maybeScheduleMeasurementFrame(); | |
47 _pendingMeasurementFrameCallbacks.add(callback); | 54 _pendingMeasurementFrameCallbacks.add(callback); |
48 } | 55 } |
49 | 56 |
50 /** | 57 /** |
51 * Run all pending measurement frames evaluating them in a single batch | 58 * Returns a [Future] whose value will be the result of evaluating |
| 59 * [computeValue] during the next safe measurement interval. |
| 60 * The next safe measurement interval is after the current event loop has |
| 61 * unwound but before the browser has rendered the page. |
| 62 * It is important that the [computeValue] function only queries the html |
| 63 * layout and html in any way. |
| 64 */ |
| 65 Future _createMeasurementFuture(ComputeValue computeValue, |
| 66 Completer completer) { |
| 67 if (_pendingRequests === null) { |
| 68 _pendingRequests = <_MeasurementRequest>[]; |
| 69 _maybeScheduleMeasurementFrame(); |
| 70 } |
| 71 _pendingRequests.add(new _MeasurementRequest(computeValue, completer)); |
| 72 return completer.future; |
| 73 } |
| 74 |
| 75 /** |
| 76 * Complete all pending measurement futures evaluating them in a single batch |
52 * so that the the browser is guaranteed to avoid multiple layouts. | 77 * so that the the browser is guaranteed to avoid multiple layouts. |
53 */ | 78 */ |
54 void _runMeasurementFrames() { | 79 void _completeMeasurementFutures() { |
55 if (_nextMeasurementFrameScheduled == false || _inMeasurementFrame) { | 80 if (_nextMeasurementFrameScheduled == false) { |
56 // Ignore spurious call to this function. | 81 // Ignore spurious call to this function. |
57 return; | 82 return; |
58 } | 83 } |
59 | 84 |
60 _inMeasurementFrame = true; | 85 _nextMeasurementFrameScheduled = false; |
61 | 86 // We must compute all new values before fulfilling the futures as |
62 final layoutCallbacks = <LayoutCallback>[]; | 87 // the onComplete callbacks for the futures could modify the DOM making |
63 while (!_pendingMeasurementFrameCallbacks.isEmpty()) { | 88 // subsequent measurement calculations expensive to compute. |
64 MeasurementCallback measurementCallback = | 89 if (_pendingRequests !== null) { |
65 _pendingMeasurementFrameCallbacks.removeFirst(); | 90 for (_MeasurementRequest request in _pendingRequests) { |
66 try { | 91 try { |
67 final layoutCallback = measurementCallback(); | 92 request.value = request.computeValue(); |
68 if (layoutCallback != null) { | 93 } catch(var e) { |
69 layoutCallbacks.add(layoutCallback); | 94 request.value = e; |
| 95 request.exception = true; |
70 } | 96 } |
71 } catch (Object e) { | |
72 window.console.error( | |
73 'Caught exception in measurement frame callback: ${e}'); | |
74 // TODO(jacobr): throw this exception again in the correct way. | |
75 } | 97 } |
76 } | 98 } |
77 | 99 |
78 _inMeasurementFrame = false; | 100 final completedRequests = _pendingRequests; |
79 _nextMeasurementFrameScheduled = false; | 101 final readyMeasurementFrameCallbacks = _pendingMeasurementFrameCallbacks; |
| 102 _pendingRequests = null; |
| 103 _pendingMeasurementFrameCallbacks = null; |
| 104 if (completedRequests !== null) { |
| 105 for (_MeasurementRequest request in completedRequests) { |
| 106 if (request.exception) { |
| 107 request.completer.completeException(request.value); |
| 108 } else { |
| 109 request.completer.complete(request.value); |
| 110 } |
| 111 } |
| 112 } |
80 | 113 |
81 for (LayoutCallback layoutCallback in layoutCallbacks) { | 114 if (readyMeasurementFrameCallbacks !== null) { |
82 try { | 115 for (TimeoutHandler handler in readyMeasurementFrameCallbacks) { |
83 layoutCallback(); | 116 // TODO(jacobr): wrap each call to a handler in a try-catch block. |
84 } catch (Object e) { | 117 handler(); |
85 window.console.error('Caught exception in layout callback: ${e}'); | |
86 // TODO(jacobr): throw this exception again in the correct way. | |
87 } | 118 } |
88 } | 119 } |
89 } | 120 } |
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