javascript - node.js redis 异步性质令人困惑

Question

我正在如下使用 redis，遇到问题是因为 on('message') 似乎被异步调用了吗？

var subscriber = redis.createClient(port, host);
subscriber.subscribe('something');

subscriber.on('message', function(channel, message) {
    console.log('got message');

    // I use generator here

    var generator = myGenerator();
    var waitFunciton = generator.next().value;

    waitFunction(function(err, data) {

        var result = generator.next().value;

        // do something with result
        console.log('returning result');
    });

});

我希望看到

'got message'  
'returning result'
'got message'  
'returning result'

按顺序。

有时我会看到以下内容

'got message'
'got message'
'returning result'

看到缺少'返回结果'，程序卡住了。

我该如何修复程序？

** 编辑 **

var myGenerator = function* (arg) {
    main = {};
    main.messenger = new Backbone.Model();

    // performs something heavy

    // at the end of the heavy work,
    // main.messenger.trigger('done') is called

    _.extend(main, {
        wait: function (callback) {
            return main.messenger.once('done', callback);

        }
    });

    yield _.bind(main.wait, main);

    // since I have results at hand I'm returning result next time when I'm called

    var result;

    return result;

}

Answer 1

您的代码卡住了，因为您在第一次调用 myGenerator 后仅触发了一次 done。 next() 调用不会使生成器函数从头开始执行，因此带有 log('returning result') 的 callback 只执行一次。

您可以修改您的 main.wait 函数来检查您的繁重计算是否已经完成并立即调用回调。

var myGenerator = function* (arg) {
    main = {};
    main.messenger = new Backbone.Model();

    // performs something heavy

    // at the end of the heavy work,
    // main.messenger.trigger('done') is called
    // main.messenger.set('computationDone', true);

    _.extend(main, {
        wait: function (callback) {
            if (main.messenger.get('computationDone') === true){
                 callback(); //filled with some data of course
            } else {
                return main.messenger.once('done', callback);
            }
        }
    });

    yield _.bind(main.wait, main);

    // since I have results at hand I'm returning result next time when I'm called

    var result;

    return result;
}