JavaScript中的互斥体 – 这看起来像是一个正确的实现吗？

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这不是一个完全严肃的问题,更多的是淋浴：JavaScript的await关键字应该允许一些非常像平均“并发语言”中的互斥体的东西.

function Mutex() {
    var self = this; // still unsure about how "this" is captured
    var mtx = new Promise(t => t()); // fulfilled promise ≡ unlocked mutex
    this.lock = async function() {
        await mtx;
        mtx = new Promise(t => {
            self.unlock = () => t();
        });
    }
}
// Lock
await mutex.lock();
// Unlock
mutex.unlock();

这是一个正确的实现(除了正确的错误处理)？而且……我可以拥有C -RAII式锁定装置吗？

解决方法:

您的实施允许尽可能多的消费者获得锁定要求;每次锁定调用都会等待一个承诺：

function Mutex() {
    var self = this; // still unsure about how "this" is captured
    var mtx = new Promise(t => t()); // fulfilled promise ≡ unlocked mutex
    this.lock = async function() {
        await mtx;
        mtx = new Promise(t => {
            self.unlock = () => t();
        });
    }
}

const mutex = new Mutex();

(async () => {
  await Promise.resolve();
  await mutex.lock();
  console.log("A got the lock");
})();
(async () => {
  await Promise.resolve();
  await mutex.lock();
  console.log("B got the lock");
})();

您需要实现一个promise队列,为每个锁请求创建一个新队列.

附注：

>新的Promise(t => t())可以更简单和惯用地写成Promise.resolve():-)
>如果你使用像这样的箭头功能,就不需要自己;箭头函数关闭它们创建的位置(就像关闭变量一样)
>解锁成为锁定承诺的解析值可能是有意义的,所以只有获得锁定的代码才能释放它

像这样的东西：

function Mutex() {
    let current = Promise.resolve();
    this.lock = () => {
        let _resolve;
        const p = new Promise(resolve => {
            _resolve = () => resolve();
        });
        // Caller gets a promise that resolves when the current outstanding
        // lock resolves
        const rv = current.then(() => _resolve);
        // Don't allow the next request until the new promise is done
        current = p;
        // Return the new promise
        return rv;
    };
}

实例：

"use strict";
function Mutex() {
    let current = Promise.resolve();
    this.lock = () => {
        let _resolve;
        const p = new Promise(resolve => {
            _resolve = () => resolve();
        });
        // Caller gets a promise that resolves when the current outstanding
        // lock resolves
        const rv = current.then(() => _resolve);
        // Don't allow the next request until the new promise is done
        current = p;
        // Return the new promise
        return rv;
    };
}

const rand = max => Math.floor(Math.random() * max);

const delay = (ms, value) => new Promise(resolve => setTimeout(resolve, ms, value));

const mutex = new Mutex();

function go(name) {
    (async () => {
        console.log(name + " random initial delay");
        await delay(rand(50));
        console.log(name + " requesting lock");
        const unlock = await mutex.lock();
        console.log(name + " got lock");
        await delay(rand(1000));
        console.log(name + " releasing lock");
        unlock();
    })();
}
go("A");
go("B");
go("C");
go("D");

.as-console-wrapper {
  max-height: 100% !important;
}

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