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<h1 class="page-title">Source: util/Scheduler.js</h1>
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<pre class="prettyprint source linenums"><code>/**
* Scheduler.
*
* @author Alain Pitiot
* @version 2020.1
* @copyright (c) 2020 Ilixa Ltd. ({@link http://ilixa.com})
* @license Distributed under the terms of the MIT License
*/
/**
* &lt;p>A scheduler helps run the main loop by managing scheduled functions,
* called tasks, after each frame is displayed.&lt;/p>
*
* &lt;p>
* Tasks are either another [Scheduler]{@link module:util.Scheduler}, or a
* JavaScript functions returning one of the following codes:
* &lt;ul>
* &lt;li>Scheduler.Event.NEXT: Move onto the next task *without* rendering the scene first.&lt;/li>
* &lt;li>Scheduler.Event.FLIP_REPEAT: Render the scene and repeat the task.&lt;/li>
* &lt;li>Scheduler.Event.FLIP_NEXT: Render the scene and move onto the next task.&lt;/li>
* &lt;li>Scheduler.Event.QUIT: Quit the scheduler.&lt;/li>
* &lt;/ul>
* &lt;/p>
*
* &lt;p> It is possible to create sub-schedulers, e.g. to handle loops.
* Sub-schedulers are added to a parent scheduler as a normal
* task would be by calling [scheduler.add(subScheduler)]{@link module:util.Scheduler#add}.&lt;/p>
*
* &lt;p> Conditional branching is also available:
* [scheduler.addConditionalBranches]{@link module:util.Scheduler#addConditional}&lt;/p>
*
*
* @name module:util.Scheduler
* @class
* @param {module:core.PsychoJS} psychoJS - the PsychoJS instance
*
*/
export class Scheduler
{
constructor(psychoJS)
{
this._psychoJS = psychoJS;
this._taskList = [];
this._currentTask = undefined;
this._argsList = [];
this._currentArgs = undefined;
this._stopAtNextUpdate = false;
this._stopAtNextTask = false;
this._status = Scheduler.Status.STOPPED;
}
/**
* Get the status of the scheduler.
*
* @name module:util.Scheduler#status
* @public
* @returns {module:util.Scheduler#Status} the status of the scheduler
*/
get status() { return this._status; }
/**
* Task to be run by the scheduler.
*
* @callback module:util.Scheduler~Task
* @param {*} [args] optional arguments
*/
/**
* Schedule a new task.
*
* @name module:util.Scheduler#add
* @public
* @param {module:util.Scheduler~Task | module:util.Scheduler} task - the task to be scheduled
* @param {...*} args - arguments for that task
*/
add(task, ...args) {
this._taskList.push(task);
this._argsList.push(args);
}
/**
* Condition evaluated when the task is run.
*
* @callback module:util.Scheduler~Condition
* @return {boolean}
*/
/**
* Schedule a series of task or another, based on a condition.
*
* &lt;p>Note: the tasks are [sub-schedulers]{@link module:util.Scheduler}.&lt;/p>
*
* @name module:util.Scheduler#addConditional
* @public
* @param {module:util.Scheduler~Condition} condition - the condition
* @param {module:util.Scheduler} thenScheduler - the [Scheduler]{@link module:util.Scheduler} to be run if the condition is satisfied
* @param {module:util.Scheduler} elseScheduler - the [Scheduler]{@link module:util.Scheduler} to be run if the condition is not satisfied
*/
addConditional(condition, thenScheduler, elseScheduler) {
const self = this;
let task = function () {
if (condition())
self.add(thenScheduler);
else
self.add(elseScheduler);
return Scheduler.Event.NEXT;
};
this.add(task);
}
/**
* Start this scheduler.
*
* &lt;p>Note: tasks are run after each animation frame.&lt;/p>
*
* @name module:util.Scheduler#start
* @public
*/
start() {
const self = this;
let update = () => {
// stop the animation if need be:
if (self._stopAtNextUpdate) {
self._status = Scheduler.Status.STOPPED;
return;
}
// self._psychoJS.window._writeLogOnFlip();
// run the next scheduled tasks until a scene render is requested:
const state = self._runNextTasks();
if (state === Scheduler.Event.QUIT) {
self._status = Scheduler.Status.STOPPED;
return;
}
// render the scene in the window:
self._psychoJS.window.render();
// request a new frame:
requestAnimationFrame(update);
};
// start the animation:
requestAnimationFrame(update);
}
/**
* Stop this scheduler.
*
* @name module:util.Scheduler#stop
* @public
*/
stop() {
this._status = Scheduler.Status.STOPPED;
this._stopAtNextTask = true;
this._stopAtNextUpdate = true;
}
/**
* Run the next scheduled tasks, in sequence, until a rendering of the scene is requested.
*
* @name module:util.Scheduler#_runNextTasks
* @private
* @return {module:util.Scheduler#Event} the state of the scheduler after the last task ran
*/
_runNextTasks() {
this._status = Scheduler.Status.RUNNING;
let state = Scheduler.Event.NEXT;
while (state === Scheduler.Event.NEXT) {
// check if we need to quit:
if (this._stopAtNextTask)
return Scheduler.Event.QUIT;
// if there is no current task, we look for the next one in the list or quit if there is none:
if (typeof this._currentTask == 'undefined') {
// a task is available in the taskList:
if (this._taskList.length > 0) {
this._currentTask = this._taskList.shift();
this._currentArgs = this._argsList.shift();
}
// the taskList is empty: we quit
else {
this._currentTask = undefined;
this._currentArgs = undefined;
return Scheduler.Event.QUIT;
}
} else {
// we are repeating a task
}
// if the current task is a function, we run it:
if (this._currentTask instanceof Function) {
state = this._currentTask(...this._currentArgs);
}
// otherwise, we assume that the current task is a scheduler and we run its tasks until a rendering
// of the scene is required.
// note: "if (this._currentTask instanceof Scheduler)" does not work because of CORS...
else {
state = this._currentTask._runNextTasks();
if (state === Scheduler.Event.QUIT) {
// if the experiment has not ended, we move onto the next task:
if (!this._psychoJS.experiment.experimentEnded)
state = Scheduler.Event.NEXT;
}
}
// if the current task's return status is FLIP_REPEAT, we will re-run it, otherwise
// we move onto the next task:
if (state !== Scheduler.Event.FLIP_REPEAT) {
this._currentTask = undefined;
this._currentArgs = undefined;
}
}
return state;
}
}
/**
* Events.
*
* @name module:util.Scheduler#Event
* @enum {Symbol}
* @readonly
* @public
*/
Scheduler.Event = {
/**
* Move onto the next task *without* rendering the scene first.
*/
NEXT: Symbol.for('NEXT'),
/**
* Render the scene and repeat the task.
*/
FLIP_REPEAT: Symbol.for('FLIP_REPEAT'),
/**
* Render the scene and move onto the next task.
*/
FLIP_NEXT: Symbol.for('FLIP_NEXT'),
/**
* Quit the scheduler.
*/
QUIT: Symbol.for('QUIT')
};
/**
* Status.
*
* @name module:util.Scheduler#Status
* @enum {Symbol}
* @readonly
* @public
*/
Scheduler.Status = {
/**
* The Scheduler is running.
*/
RUNNING: Symbol.for('RUNNING'),
/**
* The Scheduler is stopped.
*/
STOPPED: Symbol.for('STOPPED')
};</code></pre>
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