等待几个网络工作者完成 [英] Wait for several web workers to finish

问题描述

我有一个创建多个webworkers的脚本，这些webworkers执行一些工作并在完成后发送消息。

I have a script that creates several webworkers, these webworkers perform some work and send a message when they finish.

问题是我需要从所有这些结果中获取结果然后计算最终解决方案。在其他工作中，他们计算出问题的部分解决方案，主线程使用这些部分解决方案来生成最终答案。

The problem is I need to get the result from all of them and then compute a final solution. In other works, they work out a partial solution of the problem and the main thread uses those partial solutions to generate the final answer.

我怎么能等待所有这些线程完成，Javascript中是否存在类似Java中的invokeAll？

How could I wait for all those threads to finish, is there something in Javascript like invokeAll in Java?

或多或少，我在主线程中的内容：

More or less, what I have in my main thread:

var data = [];

function createWorker(i) {
    var v = new Worker('js/worker.js');
    v.postMessage(i);
    v.onmessage = function(event){
        data.push(event.data);
    };
}

for(var i = 0; i < 100; i++) {
    createWorker(i);
}

//Wait until all have finished somehow

推荐答案

收到最后一个数据后，请调用您的计算最终解决方案函数：

When the last piece of data is received, call your compute-the-final-solution function:

var data = [];

function createWorker(i) {
    var v = new Worker('js/worker.js');
    v.postMessage(i);
    v.onmessage = function(event){
        data.push(event.data);
        if (data.length === 100) {               // <====
            computeFinalSolution();              // <====
        }                                        // <====
    };
}

for(var i = 0; i < 100; i++) {
    createWorker(i);
}

显然，根据需要参数化，但 createWorker 目前没有参数化 i ，所以...

Obviously, parameterize that as you consider necessary, but createWorker isn't currently parameterized other than i, so...

注意数据中的条目可能不符合规定。 i == 0 的工作人员可能无法完成 i == 1 ，只是因为线程调度的变幻莫测或者工作需要更多处理。如果你需要它们，它很容易完成，但我们必须在每次完成时添加一个计数器（或通过数据循环检查）：

Note that the entries in data may not be in order. The worker for i == 0 might not complete until after the worker for i == 1, just because of the vagaries of thread scheduling or if the work requires more processing. If you need them in order, it's easily done, but we have to add a counter (or loop through data on each completion to check):

var data = [];
var dataReceived = 0;

function createWorker(i) {
    var v = new Worker('js/worker.js');
    v.postMessage(i);
    v.onmessage = function(event){
        data[i] = event.data;                    // <====
        if (++dataReceived === 100) {            // <====
            computeFinalSolution();              // <====
        }                                        // <====
    };
}

for(var i = 0; i < 100; i++) {
    createWorker(i);
}

---

如果你想要更多现代，灵活的方法，考虑使用promises，从ES2015（又名ES6）开始，它是JavaScript原生的，并且可以在旧的JavaScript引擎上使用polyfilled：

---

If you want a more modern, flexible approach, consider using promises, which are native to JavaScript as of ES2015 (aka ES6) and can be polyfilled for use on older JavaScript engines:

function createWorker(i) {
    return new Promise(function(resolve) {
        var v = new Worker('js/worker.js');
        v.postMessage(i);
        v.onmessage = function(event){
            resolve(event.data);
        };
    });
}

var promises = [];
for(var i = 0; i < 100; i++) {
    promises.push(createWorker(i));
}
Promise.all(promises)
    .then(function(data) {
        // `data` has the results, compute the final solution
    });

这也有数据的优势包含结果按顺序，我们不必自己做这项工作。

This also has the advantage that data will contain the results in order, we don't have to do that work ourselves.

以上内容与您当前的代码一致，似乎没有任何错误准备。但通常最好做错误处理：

The above is in line with your current code, which doesn't appear to have any provision for errors. But it's usually best to do error handling:

function createWorker(i) {
    return new Promise(function(resolve, reject) {
        var v = new Worker('js/worker.js');
        v.postMessage(i);
        v.onmessage = function(event){
            // If you report errors via messages, you'd have a branch here for checking
            // for an error and either calling `reject` or `resolve` as appropriate.
            resolve(event.data);
        };
        // EITHER:
        v.onerror = reject; // Rejects the promise if an error is raised by the web worker, passing along the ErrorEvent
        // OR:
        v.onerror = function(event) {
            // Rejects the promise using the error associated with the ErrorEvent
            reject(event.error);
        };
    });
}

var promises = [];
for(var i = 0; i < 100; i++) {
    promises.push(createWorker(i));
}
Promise.all(promises)
    .then(function(data) {
        // `data` has the results, compute the final solution
    })
    .catch(function(error) {
        // something went wrong
    });

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