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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 part of html; | |
6 | |
7 typedef void _MicrotaskCallback(); | |
8 | |
9 /** | |
10 * This class attempts to invoke a callback as soon as the current event stack | |
11 * unwinds, but before the browser repaints. | |
12 */ | |
13 abstract class _MicrotaskScheduler { | |
14 bool _nextMicrotaskFrameScheduled = false; | |
15 final _MicrotaskCallback _callback; | |
16 | |
17 _MicrotaskScheduler(this._callback); | |
18 | |
19 /** | |
20 * Creates the best possible microtask scheduler for the current platform. | |
21 */ | |
22 factory _MicrotaskScheduler.best(_MicrotaskCallback callback) { | |
23 if (Window._supportsSetImmediate) { | |
24 return new _SetImmediateScheduler(callback); | |
25 } else if (MutationObserver.supported) { | |
26 return new _MutationObserverScheduler(callback); | |
27 } | |
28 return new _PostMessageScheduler(callback); | |
29 } | |
30 | |
31 /** | |
32 * Schedules a microtask callback if one has not been scheduled already. | |
33 */ | |
34 void maybeSchedule() { | |
35 if (this._nextMicrotaskFrameScheduled) { | |
36 return; | |
37 } | |
38 this._nextMicrotaskFrameScheduled = true; | |
39 this._schedule(); | |
40 } | |
41 | |
42 /** | |
43 * Does the actual scheduling of the callback. | |
44 */ | |
45 void _schedule(); | |
46 | |
47 /** | |
48 * Handles the microtask callback and forwards it if necessary. | |
49 */ | |
50 void _onCallback() { | |
51 // Ignore spurious messages. | |
52 if (!_nextMicrotaskFrameScheduled) { | |
53 return; | |
54 } | |
55 _nextMicrotaskFrameScheduled = false; | |
56 this._callback(); | |
57 } | |
58 } | |
59 | |
60 /** | |
61 * Scheduler which uses window.postMessage to schedule events. | |
62 */ | |
63 class _PostMessageScheduler extends _MicrotaskScheduler { | |
64 final _MICROTASK_MESSAGE = "DART-MICROTASK"; | |
65 | |
66 _PostMessageScheduler(_MicrotaskCallback callback): super(callback) { | |
67 // Messages from other windows do not cause a security risk as | |
68 // all we care about is that _handleMessage is called | |
69 // after the current event loop is unwound and calling the function is | |
70 // a noop when zero requests are pending. | |
71 window.onMessage.listen(this._handleMessage); | |
72 } | |
73 | |
74 void _schedule() { | |
75 window.postMessage(_MICROTASK_MESSAGE, "*"); | |
76 } | |
77 | |
78 void _handleMessage(e) { | |
79 this._onCallback(); | |
80 } | |
81 } | |
82 | |
83 /** | |
84 * Scheduler which uses a MutationObserver to schedule events. | |
85 */ | |
86 class _MutationObserverScheduler extends _MicrotaskScheduler { | |
87 MutationObserver _observer; | |
88 Element _dummy; | |
89 | |
90 _MutationObserverScheduler(_MicrotaskCallback callback): super(callback) { | |
91 // Mutation events get fired as soon as the current event stack is unwound | |
92 // so we just make a dummy event and listen for that. | |
93 _observer = new MutationObserver(this._handleMutation); | |
94 _dummy = new DivElement(); | |
95 _observer.observe(_dummy, attributes: true); | |
96 } | |
97 | |
98 void _schedule() { | |
99 // Toggle it to trigger the mutation event. | |
100 _dummy.hidden = !_dummy.hidden; | |
101 } | |
102 | |
103 _handleMutation(List<MutationRecord> mutations, MutationObserver observer) { | |
104 this._onCallback(); | |
105 } | |
106 } | |
107 | |
108 /** | |
109 * Scheduler which uses window.setImmediate to schedule events. | |
110 */ | |
111 class _SetImmediateScheduler extends _MicrotaskScheduler { | |
112 _SetImmediateScheduler(_MicrotaskCallback callback): super(callback); | |
113 | |
114 void _schedule() { | |
115 window._setImmediate(_handleImmediate); | |
116 } | |
117 | |
118 void _handleImmediate() { | |
119 this._onCallback(); | |
120 } | |
121 } | |
122 | |
123 List<TimeoutHandler> _pendingMicrotasks; | |
124 _MicrotaskScheduler _microtaskScheduler = null; | |
125 | |
126 void _maybeScheduleMicrotaskFrame() { | |
127 if (_microtaskScheduler == null) { | |
128 _microtaskScheduler = | |
129 new _MicrotaskScheduler.best(_completeMicrotasks); | |
130 } | |
131 _microtaskScheduler.maybeSchedule(); | |
132 } | |
133 | |
134 /** | |
135 * Registers a [callback] which is called after the current execution stack | |
136 * unwinds. | |
137 */ | |
138 void _addMicrotaskCallback(TimeoutHandler callback) { | |
139 if (_pendingMicrotasks == null) { | |
140 _pendingMicrotasks = <TimeoutHandler>[]; | |
141 _maybeScheduleMicrotaskFrame(); | |
142 } | |
143 _pendingMicrotasks.add(callback); | |
144 } | |
145 | |
146 | |
147 /** | |
148 * Complete all pending microtasks. | |
149 */ | |
150 void _completeMicrotasks() { | |
151 var callbacks = _pendingMicrotasks; | |
152 _pendingMicrotasks = null; | |
153 for (var callback in callbacks) { | |
154 callback(); | |
155 } | |
156 } | |
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