performance.eventLoopUtilization([util1][,util2])

• util1 <Object> 先前调用 eventLoopUtilization() 的结果
• util2 <Object>
• 返回 <Object>
  • idle <number>
  • active <number>
  • utilization <number>

eventLoopUtilization() 方法返回包含事件循环作为高解析度毫秒计时器的既空闲又活动的累积持续时间的对象。 utilization 值是计算的事件循环利用率 (ELU)。

它表示事件循环在事件循环的事件提供者（例如 epoll_wait）之外花费的时间百分比。 不考虑其他 CPU 空闲时间。 以下是主要空闲进程如何具有高 ELU 的示例。

'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);
});

这是因为对 child_process.spawnSync() 的调用阻止了事件循环的进行。

传入用户定义的对象而不是先前调用 eventLoopUtilization() 的结果将导致未定义的行为。 不保证返回值反映事件循环的任何正确状态。

• 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);
});

Although 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.