react-native/Libraries/Interaction/JSEventLoopWatchdog.js

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/**
* Copyright (c) 2015-present, Facebook, Inc.
* All rights reserved.
*
* This source code is licensed under the BSD-style license found in the
* LICENSE file in the root directory of this source tree. An additional grant
* of patent rights can be found in the PATENTS file in the same directory.
*
* @providesModule JSEventLoopWatchdog
* @flow
*/
'use strict';
const performanceNow = require('performanceNow');
type Handler = {
onIterate?: () => void;
onStall: (params: {lastInterval: number}) => string;
};
/**
* A utility for tracking stalls in the JS event loop that prevent timers and
* other events from being processed in a timely manner.
*
* The "stall" time is defined as the amount of time in access of the acceptable
* threshold, which is typically around 100-200ms. So if the treshold is set to
* 100 and a timer fires 150 ms later than it was scheduled because the event
* loop was tied up, that would be considered a 50ms stall.
*
* By default, logs stall events to the console when installed. Can also be
* queried with `getStats`.
*/
const JSEventLoopWatchdog = {
getStats: function(): Object {
return {stallCount, totalStallTime, longestStall, acceptableBusyTime};
},
reset: function() {
console.log('JSEventLoopWatchdog: reset');
totalStallTime = 0;
stallCount = 0;
longestStall = 0;
},
addHandler: function(handler: Handler) {
handlers.push(handler);
},
install: function({thresholdMS}: {thresholdMS: number}) {
acceptableBusyTime = thresholdMS;
if (installed) {
return;
}
installed = true;
let lastInterval = performanceNow();
function iteration() {
const now = performanceNow();
const busyTime = now - lastInterval;
if (busyTime >= thresholdMS) {
const stallTime = busyTime - thresholdMS;
stallCount++;
totalStallTime += stallTime;
longestStall = Math.max(longestStall, stallTime);
let msg = `JSEventLoopWatchdog: JS thread busy for ${busyTime}ms. ` +
`${totalStallTime}ms in ${stallCount} stalls so far. `;
handlers.forEach((handler) => {
msg += handler.onStall({lastInterval});
});
console.log(msg);
}
handlers.forEach((handler) => {
handler.onIterate && handler.onIterate();
});
lastInterval = now;
setTimeout(iteration, thresholdMS / 5);
}
iteration();
},
};
let acceptableBusyTime = 0;
let installed = false;
let totalStallTime = 0;
let stallCount = 0;
let longestStall = 0;
const handlers: Array<Handler> = [];
module.exports = JSEventLoopWatchdog;