performance eventlooputilization util1 util2

• util1 {Object} The result of a previous call to eventLoopUtilization()
• util2 {Object} The result of a previous call to eventLoopUtilization() prior to util1
• Returns {Object}
  • idle {number}
  • active {number}
  • utilization {number}

The eventLoopUtilization() method returns an object that contains the cumulative duration of time the event loop has been both idle and active as a high resolution milliseconds timer. The utilization value is the calculated Event Loop Utilization (ELU). If bootstrapping has not yet finished, the properties have the value of 0.

util1 and util2 are optional parameters.

If util1 is passed then the delta between the current call’s active and idle times are calculated and returned (similar to [process.hrtime()][]). Likewise the adjusted utilization value is calculated.

If util1 and util2 are both passed then the calculation adjustments are done between the two arguments. This is a convenience option because unlike [process.hrtime()][] additional work is done to calculate the ELU.

ELU is similar to CPU utilization except that it is calculated using high precision wall-clock time. It represents the percentage of time the event loop has spent outside the event loop’s event provider (e.g. epoll_wait). No other CPU idle time is taken into consideration. The following is an example of how a mostly idle process will have a high ELU.

'use strict';
const { eventLoopUtilization } = require('perf_hooks').performance;
const { spawnSync } = require('child_process');
setImmediate(() => {
  const elu = eventLoopUtilization();
  spawnSync('sleep', ['5']);
  console.log(eventLoopUtilization(elu).utilization);
});

While the CPU is mostly idle while running this script the value of utilization is 1. This is because the call to [child_process.spawnSync()][] blocks the event loop from proceeding.

Passing in a user-defined object instead of the result of a previous call to eventLoopUtilization() will lead to undefined behavior. The return values are not guaranteed to reflect any correct state of the event loop.