在node.js中编写嵌套的非阻塞循环

Question

How to properly write the following set of loops in Node.Js without blocking the event loop or without causing out of memory error.

What I have tried so far includes

• Combinations of setImmediate()/setInterval()
• The Async module see my code here
• Thread_a_gogo (this module is no more maintained)

The code.

for(var i = 0; i < 2000; i++)
    for(var j = 0; i < 2000; j++)
        for(var k = 0; k < 2000; k++)
            console.log(i + ":" + j + ":" + k);

Also created a JSFiddle to play around here

Answer 1

Not really sure what your use-case is. Javascript is blocking as it's single threaded, it would have to run the loop before moving to something else.

You could for example use a generator to run each iteration on an event though.

function* ticker() {
  for(let i = 0; i < 10; i++)
    for(let j = 0; i < 10; j++)
        for(let k = 0; k < 10; k++)
            yield[i, j, k];
}

const gen = ticker();

setInterval(() => console.log(gen.next().value), 500);

console.log('I am at the end (called straight away)');

Answer 2

You need to combine setImmediate / setTimeout /etc. with the async.js library. async.each is only for orchestration, it doesn't provide any asynchrony itself.

function getPerm(reducedWordList, callback) {
    var sevenLtrWords = _.filter(reducedWordList, word => word.length == 7); 
    var fourLtrWords = _.filter(reducedWordList, word => word.length == 4); 

    async.each(sevenLtrWords, (i, cb) => {
        async.each(sevenLtrWords, (j, cb) => {
            async.each(fourLtrWords, (k, cb) => {
                console.log(i + " " + j + " " + k); 
                setTimeout(cb, 0);
            }, cb);
        }, cb);
    }, callback);
}