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/*****************************************************************************
* Open MCT, Copyright (c) 2009-2021, United States Government
* as represented by the Administrator of the National Aeronautics and Space
* Administration. All rights reserved.
*
* Open MCT is licensed under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* http://www.apache.org/licenses/LICENSE-2.0.
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
* Open MCT includes source code licensed under additional open source
* licenses. See the Open Source Licenses file (LICENSES.md) included with
* this source code distribution or the Licensing information page available
* at runtime from the About dialog for additional information.
*****************************************************************************/
class Ticker {
constructor() {
this.callbacks = [];
this.last = new Date() - 1000;
}
/**
* Calls functions every second, as close to the actual second
* tick as is feasible.
* @constructor
* @memberof utils/clock
*/
tick() {
const timestamp = new Date();
const millis = timestamp % 1000;
// Only update callbacks if a second has actually passed.
if (timestamp >= this.last + 1000) {
this.callbacks.forEach(function (callback) {
callback(timestamp);
});
this.last = timestamp - millis;
}
// Try to update at exactly the next second
this.timeoutHandle = setTimeout(() => {
this.tick();
}, 1000 - millis, true);
}
/**
* Listen for clock ticks. The provided callback will
* be invoked with the current timestamp (in milliseconds
* since Jan 1 1970) at regular intervals, as near to the
* second boundary as possible.
*
* @param {Function} callback callback to invoke
* @returns {Function} a function to unregister this listener
*/
listen(callback) {
if (this.callbacks.length === 0) {
this.tick();
}
this.callbacks.push(callback);
// Provide immediate feedback
callback(this.last);
// Provide a deregistration function
return () => {
this.callbacks = this.callbacks.filter(function (cb) {
return cb !== callback;
});
if (this.callbacks.length === 0) {
clearTimeout(this.timeoutHandle);
}
};
}
}
let ticker = new Ticker();
export default ticker;
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