| Chris Craik | b122baf | 2015-03-05 13:58:42 -0800 | [diff] [blame^] | 1 | <!DOCTYPE html> |
| 2 | <!-- |
| 3 | Copyright (c) 2013 The Chromium Authors. All rights reserved. |
| 4 | Use of this source code is governed by a BSD-style license that can be |
| 5 | found in the LICENSE file. |
| 6 | --> |
| 7 | <link rel="import" href="/base/raf.html"> |
| 8 | |
| 9 | <script> |
| 10 | 'use strict'; |
| 11 | |
| 12 | tv.exportTo('tv.b', function() { |
| 13 | /** |
| 14 | * A task is a combination of a run callback, a set of subtasks, and an after |
| 15 | * task. |
| 16 | * |
| 17 | * When executed, a task does the following things: |
| 18 | * 1. Runs its callback |
| 19 | * 2. Runs its subtasks |
| 20 | * 3. Runs its after callback. |
| 21 | * |
| 22 | * The list of subtasks and after task can be mutated inside step #1 but as |
| 23 | * soon as the task's callback returns, the subtask list and after task is |
| 24 | * fixed and cannot be changed again. |
| 25 | * |
| 26 | * Use task.after().after().after() to describe the toplevel passes that make |
| 27 | * up your computation. Then, use subTasks to add detail to each subtask as it |
| 28 | * runs. For example: |
| 29 | * var pieces = []; |
| 30 | * taskA = new Task(function() { pieces = getPieces(); }); |
| 31 | * taskA.after(function(taskA) { |
| 32 | * pieces.forEach(function(piece) { |
| 33 | * taskA.subTask(function(taskB) { piece.process(); }, this); |
| 34 | * }); |
| 35 | * }); |
| 36 | * |
| 37 | * @constructor |
| 38 | */ |
| 39 | function Task(runCb, thisArg) { |
| 40 | if (runCb !== undefined && thisArg === undefined) |
| 41 | throw new Error('Almost certainly, you meant to pass a thisArg.'); |
| 42 | this.runCb_ = runCb; |
| 43 | this.thisArg_ = thisArg; |
| 44 | this.afterTask_ = undefined; |
| 45 | this.subTasks_ = []; |
| 46 | } |
| 47 | |
| 48 | Task.prototype = { |
| 49 | /* |
| 50 | * See constructor documentation on semantics of subtasks. |
| 51 | */ |
| 52 | subTask: function(cb, thisArg) { |
| 53 | if (cb instanceof Task) |
| 54 | this.subTasks_.push(cb); |
| 55 | else |
| 56 | this.subTasks_.push(new Task(cb, thisArg)); |
| 57 | return this.subTasks_[this.subTasks_.length - 1]; |
| 58 | }, |
| 59 | |
| 60 | /** |
| 61 | * Runs the current task and returns the task that should be executed next. |
| 62 | */ |
| 63 | run: function() { |
| 64 | if (this.runCb_ !== undefined) |
| 65 | this.runCb_.call(this.thisArg_, this); |
| 66 | var subTasks = this.subTasks_; |
| 67 | this.subTasks_ = undefined; // Prevent more subTasks from being posted. |
| 68 | |
| 69 | if (!subTasks.length) |
| 70 | return this.afterTask_; |
| 71 | |
| 72 | // If there are subtasks, then we want to execute all the subtasks and |
| 73 | // then this task's afterTask. To make this happen, we update the |
| 74 | // afterTask of all the subtasks so the point upward to each other, e.g. |
| 75 | // subTask[0].afterTask to subTask[1] and so on. Then, the last subTask's |
| 76 | // afterTask points at this task's afterTask. |
| 77 | for (var i = 1; i < subTasks.length; i++) |
| 78 | subTasks[i - 1].afterTask_ = subTasks[i]; |
| 79 | subTasks[subTasks.length - 1].afterTask_ = this.afterTask_; |
| 80 | return subTasks[0]; |
| 81 | }, |
| 82 | |
| 83 | /* |
| 84 | * See constructor documentation on semantics of after tasks. |
| 85 | */ |
| 86 | after: function(cb, thisArg) { |
| 87 | if (this.afterTask_) |
| 88 | throw new Error('Has an after task already'); |
| 89 | if (cb instanceof Task) |
| 90 | this.afterTask_ = cb; |
| 91 | else |
| 92 | this.afterTask_ = new Task(cb, thisArg); |
| 93 | return this.afterTask_; |
| 94 | } |
| 95 | }; |
| 96 | |
| 97 | Task.RunSynchronously = function(task) { |
| 98 | var curTask = task; |
| 99 | while (curTask) |
| 100 | curTask = curTask.run(); |
| 101 | } |
| 102 | |
| 103 | /** |
| 104 | * Runs a task using raf.requestIdleCallback, returning |
| 105 | * a promise for its completion. |
| 106 | */ |
| 107 | Task.RunWhenIdle = function(task) { |
| 108 | return new Promise(function(resolve, reject) { |
| 109 | var curTask = task; |
| 110 | function runAnother() { |
| 111 | try { |
| 112 | curTask = curTask.run(); |
| 113 | } catch (e) { |
| 114 | reject(e); |
| 115 | console.error(e.stack); |
| 116 | return; |
| 117 | } |
| 118 | |
| 119 | if (curTask) { |
| 120 | tv.b.requestIdleCallback(runAnother); |
| 121 | return; |
| 122 | } |
| 123 | |
| 124 | resolve(); |
| 125 | } |
| 126 | tv.b.requestIdleCallback(runAnother); |
| 127 | }); |
| 128 | } |
| 129 | |
| 130 | return { |
| 131 | Task: Task |
| 132 | }; |
| 133 | }); |
| 134 | </script> |