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1 // Copyright (c) 2012, the Dart project authors. Please see the AUTHORS file | 1 // Copyright (c) 2012, 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 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 } | |
14 | |
15 final _MEASUREMENT_MESSAGE = "DART-MEASURE"; | |
16 List<_MeasurementRequest> _pendingRequests; | |
17 List<TimeoutHandler> _pendingMeasurementFrameCallbacks; | |
18 bool _nextMeasurementFrameScheduled = false; | |
19 bool _firstMeasurementRequest = true; | |
20 | |
21 void _maybeScheduleMeasurementFrame() { | |
22 if (_nextMeasurementFrameScheduled) return; | |
23 | |
24 _nextMeasurementFrameScheduled = true; | |
25 // postMessage gives us a way to receive a callback after the current | |
26 // event listener has unwound but before the browser has repainted. | |
27 if (_firstMeasurementRequest) { | |
28 // Messages from other windows do not cause a security risk as | |
29 // all we care about is that _onCompleteMeasurementRequests is called | |
30 // after the current event loop is unwound and calling the function is | |
31 // a noop when zero requests are pending. | |
32 window.on.message.add((e) => _completeMeasurementFutures()); | |
33 _firstMeasurementRequest = false; | |
34 } | |
35 | |
36 // TODO(jacobr): other mechanisms such as setImmediate and | |
37 // requestAnimationFrame may work better of platforms that support them. | |
38 // The key is we need a way to execute code immediately after the current | |
39 // event listener queue unwinds. | |
40 window.postMessage(_MEASUREMENT_MESSAGE, "*"); | |
41 } | |
42 | |
43 /** | |
44 * Registers a [callback] which is called after the next batch of measurements | |
45 * completes. Even if no measurements completed, the callback is triggered | |
46 * when they would have completed to avoid confusing bugs if it happened that | |
47 * no measurements were actually requested. | |
48 */ | |
49 void _addMeasurementFrameCallback(TimeoutHandler callback) { | |
50 if (_pendingMeasurementFrameCallbacks === null) { | |
51 _pendingMeasurementFrameCallbacks = <TimeoutHandler>[]; | |
52 _maybeScheduleMeasurementFrame(); | |
53 } | |
54 _pendingMeasurementFrameCallbacks.add(callback); | |
55 } | |
56 | |
57 /** | |
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 | |
77 * so that the the browser is guaranteed to avoid multiple layouts. | |
78 */ | |
79 void _completeMeasurementFutures() { | |
80 if (_nextMeasurementFrameScheduled == false) { | |
81 // Ignore spurious call to this function. | |
82 return; | |
83 } | |
84 | |
85 _nextMeasurementFrameScheduled = false; | |
86 // We must compute all new values before fulfilling the futures as | |
87 // the onComplete callbacks for the futures could modify the DOM making | |
88 // subsequent measurement calculations expensive to compute. | |
89 if (_pendingRequests !== null) { | |
90 for (_MeasurementRequest request in _pendingRequests) { | |
91 try { | |
92 request.value = request.computeValue(); | |
93 } catch(var e) { | |
94 request.value = e; | |
95 request.exception = true; | |
96 } | |
97 } | |
98 } | |
99 | |
100 final completedRequests = _pendingRequests; | |
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 } | |
113 | |
114 if (readyMeasurementFrameCallbacks !== null) { | |
115 for (TimeoutHandler handler in readyMeasurementFrameCallbacks) { | |
116 // TODO(jacobr): wrap each call to a handler in a try-catch block. | |
117 handler(); | |
118 } | |
119 } | |
120 } | |
121 | |
122 class $CLASSNAME$EXTENDS$IMPLEMENTS native "@*DOMWindow" { | 5 class $CLASSNAME$EXTENDS$IMPLEMENTS native "@*DOMWindow" { |
123 | 6 |
124 _DocumentJs get document() native "return this.document.documentElement;"; | 7 _DocumentImpl get document() native "return this.document.documentElement;"; |
125 | 8 |
126 void requestLayoutFrame(TimeoutHandler callback) { | 9 void requestLayoutFrame(TimeoutHandler callback) { |
127 _addMeasurementFrameCallback(callback); | 10 _addMeasurementFrameCallback(callback); |
128 } | 11 } |
129 | 12 |
130 $!MEMBERS | 13 $!MEMBERS |
131 } | 14 } |
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