node.js - node worker_threads console.log 在 postMessage 之后
问题描述
节点 v10.16.3
我正在运行worker_threads
节点官方文档中的示例。为了测试共享变量,我做了一些更改。这是一个例子
工作线程.js
const {
Worker,
isMainThread,
parentPort,
workerData
} = require("worker_threads");
let a = 10;
if (isMainThread) {
module.exports = async function parseJSAsync(num) {
return new Promise((resolve, reject) => {
const worker = new Worker(__filename, {
workerData: num
});
worker.on("message", resolve);
worker.on("error", reject);
worker.on("exit", code => {
if (code !== 0)
reject(new Error(`Worker stopped with exit code ${code}`));
});
for (let i = 0; i < num; i++) {
console.log("master: ", a);
a++;
}
});
};
} else {
const num = workerData;
let result = 1;
for (let i = 1; i < num; i++) {
console.log("worker: ", a);
a--;
result = result * i;
}
parentPort.postMessage(result);
}
并且有一个用于测试此示例的脚本:
const calculateFactorial = require("./work-thread");
calculateFactorial(10).then(res => console.log("res", res));
主线程和工作线程都a
可以访问。当我运行这段代码时,输出是
master: 10
master: 11
master: 12
master: 13
master: 14
master: 15
master: 16
master: 17
master: 18
master: 19
worker: 10
res 362880
worker: 9
worker: 8
worker: 7
worker: 6
worker: 5
worker: 4
worker: 3
worker: 2
我想知道为什么工人的 postMessage 早于工人的 console.log
解决方案
看起来日志记录依赖于主线程,主线程被 for 循环阻塞,直到它完成。来自工作人员的日志似乎在工作人员中调用 console.log 时被缓冲,但直到主线程被解除阻塞时才真正写出。所以这项工作是并行完成的,但不是日志记录。我还没有找到这方面的参考,但可以通过运行一个与时间相关的示例来验证它:
const {
Worker,
isMainThread
} = require('worker_threads');
if (isMainThread) {
console.log(`start time: ${Date.now()}`);
const worker = new Worker(__filename);
worker.on('exit', (code) => {
console.log(`exited with code [${code}]`);
});
worker.on('error', (err) => {
console.log(err);
});
// Block main thread for 10 seconds
const start = new Date();
while (true) {
const now = new Date();
if (now.getTime() - start.getTime() > 10000) {
console.log('brook loop');
break;
}
}
// Stop worker after another 10 seconds
setTimeout(() => worker.terminate(), 10000);
} else {
setInterval(() => console.log(Date.now()), 1000);
}
下面的输出(注释了一些关于时间的评论)
start time: 1600900685482 // written to console immediately
brook loop // written to console 10s later
1600900686512 // these 10 lines are written all at one as soon as the loop is broken. Note that even though they are written at once, the times are all 1 second apart.
1600900687515
1600900688517
1600900689518
1600900690519
1600900691520
1600900692524
1600900693525
1600900694526
1600900695527
1600900696533 // after dumping the backlog of log lines from while the main thread was blocked, new lines are now written every 1 second
1600900697536
1600900698539
1600900699540
1600900700544
1600900701550
1600900702550
1600900703556
1600900704558
exited with code [1]
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