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<!DOCTYPE html>
<!--
Copyright (c) 2013 The Chromium Authors. All rights reserved.
Use of this source code is governed by a BSD-style license that can be
found in the LICENSE file.
-->
<link rel="import" href="/tracing/base/raf.html">
<link rel="import" href="/tracing/base/timing.html">
<script>
'use strict';
tr.exportTo('tr.b', function() {
const Timing = tr.b.Timing;
/**
* A task is a combination of a run callback, a set of subtasks, and an after
* task.
*
* When executed, a task does the following things:
* 1. Runs its callback
* 2. Runs its subtasks
* 3. Runs its after callback.
*
* The list of subtasks and after task can be mutated inside step #1 but as
* soon as the task's callback returns, the subtask list and after task is
* fixed and cannot be changed again.
*
* Use task.after().after().after() to describe the toplevel passes that make
* up your computation. Then, use subTasks to add detail to each subtask as it
* runs. For example:
* var pieces = [];
* taskA = new Task(function() { pieces = getPieces(); });
* taskA.after(function(taskA) {
* pieces.forEach(function(piece) {
* taskA.subTask(function(taskB) { piece.process(); }, this);
* });
* });
*
* @constructor
*/
function Task(runCb, thisArg) {
if (runCb !== undefined && thisArg === undefined &&
runCb.prototype !== undefined) {
throw new Error('Almost certainly you meant to pass a bound callback ' +
'or thisArg.');
}
this.runCb_ = runCb;
this.thisArg_ = thisArg;
this.afterTask_ = undefined;
this.subTasks_ = [];
this.updatesUi_ = false;
}
Task.prototype = {
get name() {
return this.runCb_.name;
},
/** Sets a hint for whether or not this task updates the UI. */
set updatesUi(value) {
this.updatesUi_ = value;
},
/*
* See constructor documentation on semantics of subtasks.
*/
subTask(cb, thisArg) {
if (cb instanceof Task) {
this.subTasks_.push(cb);
} else {
this.subTasks_.push(new Task(cb, thisArg));
}
return this.subTasks_[this.subTasks_.length - 1];
},
/**
* Runs the current task and returns the task that should be executed next.
*/
run() {
if (this.runCb_ !== undefined) this.runCb_.call(this.thisArg_, this);
const subTasks = this.subTasks_;
this.subTasks_ = undefined; // Prevent more subTasks from being posted.
if (!subTasks.length) return this.afterTask_;
// If there are subtasks, then we want to execute all the subtasks and
// then this task's afterTask. To make this happen, we update the
// afterTask of all the subtasks so the point upward to each other, e.g.
// subTask[0].afterTask to subTask[1] and so on. Then, the last subTask's
// afterTask points at this task's afterTask.
for (let i = 1; i < subTasks.length; i++) {
subTasks[i - 1].afterTask_ = subTasks[i];
}
subTasks[subTasks.length - 1].afterTask_ = this.afterTask_;
return subTasks[0];
},
/*
* See constructor documentation on semantics of after tasks.
*/
after(cb, thisArg) {
if (this.afterTask_) {
throw new Error('Has an after task already');
}
if (cb instanceof Task) {
this.afterTask_ = cb;
} else {
this.afterTask_ = new Task(cb, thisArg);
}
return this.afterTask_;
},
/*
* Adds a task after the chain of tasks.
*/
enqueue(cb, thisArg) {
if (!this.afterTask_) return this.after(cb, thisArg);
return this.afterTask_.enqueue(cb, thisArg);
}
};
Task.RunSynchronously = function(task) {
let curTask = task;
while (curTask) {
curTask = curTask.run();
}
};
/**
* Runs a task using raf.requestIdleCallback, returning
* a promise for its completion.
*/
Task.RunWhenIdle = function(task) {
return new Promise(function(resolve, reject) {
let curTask = task;
function runAnother() {
try {
curTask = curTask.run();
} catch (e) {
reject(e);
return;
}
if (curTask) {
if (curTask.updatesUi_) {
tr.b.requestAnimationFrameInThisFrameIfPossible(runAnother);
} else {
tr.b.requestIdleCallback(runAnother);
}
return;
}
resolve();
}
tr.b.requestIdleCallback(runAnother);
});
};
return {
Task,
};
});
</script>
|
