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Issue 9403004: Wrapperless dart:html generator (Closed) Base URL: https://dart.googlecode.com/svn/branches/bleeding_edge/dart
Patch Set: Final version to check in. changes generator script but doesn't check in an active version of the … Created 8 years, 10 months ago
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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
3 // BSD-style license that can be found in the LICENSE file.
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" {
123
124 _DocumentJs get document() native "return this.document.documentElement;";
125
126 void requestLayoutFrame(TimeoutHandler callback) {
127 _addMeasurementFrameCallback(callback);
128 }
129
130 $!MEMBERS
131 }
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