使用setTimeout()终止Worker线程报错：Cannot read properties of undefined

问题场景 #

在Node.js v18.12.0环境下，尝试用setTimeout直接调用Worker的terminate方法终止线程时触发错误，改用包装函数则能正常运行。

错误信息 #

node:internal/worker:361
    this[kHandle].stopThread();
                  ^

TypeError: Cannot read properties of undefined (reading 'stopThread')
    at Timeout.terminate [as _onTimeout] (node:internal/worker:361:19)
    at listOnTimeout (node:internal/timers:564:17)
    at process.processTimers (node:internal/timers:507:7)

Node.js v18.12.0

报错代码 #

const { Worker } = require("node:worker_threads")
const worker = new Worker("./test.js")

const setAppTimeout = (workerName, seconds) => {
    setTimeout(workerName.terminate, seconds * 1000)
}

setAppTimeout(worker, 1)

正常运行的代码 #

const { Worker } = require("node:worker_threads")
const worker = new Worker("./test.js")

const setAppTimeout = (workerName, seconds) => {
    setTimeout(terminateWorker, seconds * 1000, workerName)
}
const terminateWorker = (workerName) => {
    workerName.terminate()
}

setAppTimeout(worker, 1)

差异原因 #

核心问题是JavaScript的this绑定规则：

• 当你直接把workerName.terminate作为参数传给setTimeout时，这个函数会被单独提取出来执行，此时它的this不再指向原Worker实例，而是变成了Timeout对象（或全局对象，取决于执行环境）。terminate方法内部需要通过this访问Worker的内部句柄kHandle，this指向错误就会导致无法读取kHandle，进而抛出错误。
• 用包装函数terminateWorker时，我们通过workerName.terminate()的形式调用，此时terminate方法的this会隐式绑定到workerName这个Worker实例上，能正确访问内部的kHandle，所以可以正常终止线程。

另外还有两种等价的写法可以解决这个问题：

• 用箭头函数绑定this：

  setTimeout(() => workerName.terminate(), seconds * 1000)
  

• 用bind手动绑定this：

  setTimeout(workerName.terminate.bind(workerName), seconds * 1000)
  

内容的提问来源于stack exchange，提问作者NoNameIdeas