异步非阻塞模型的故障处理

Question

我很难绕过节点的异步模型，我有这样的函数：

function getstream() {

    console.log('calling testAvail, Avail value is:' + available);
    testAvailability();
    console.log('Available:'+available);
    if (available || SelfSharing) {

         // Do something
         setDefaults();

         return;
    }
}

调用testAvailability()函数，定义为：

function testAvailability()
{
    console.log('entered test');
    var stat;
    var socket = io.connect('http://somedomain.com');
    socket.on('error', function() {

        console.log('There was an error at server end please try again');
        // chrome.runtime.reload();

        setTimeout(chrome.runtime.reload(),3000);
        //here i change options
        //socket = io.connect(host, options);
    });
    socket.emit('available');
    socket.on('available', function (status) {
        console.log('got status from server which is:'+ status);
        available=status;
        console.log("inside the socket.on"+available);
        console.log('leaving test, do you see any got status above?');
    });
}

我希望getstream()在完成testAvailability()和available变量的值设置之后从它离开的位置继续。

Answer 1

您需要将一个回调传递给testAvailability，然后在socket的available事件中调用它：

function testAvailability(callback)
{
    console.log('entered test');
    var stat;
    var socket = io.connect('http://somedomain.com');
    socket.on('error', function() {

        console.log('There was an error at server end please try again');
        // chrome.runtime.reload();

        setTimeout(chrome.runtime.reload(),3000);
        //here i change options
        //socket = io.connect(host, options);
    });
    socket.emit('available');
    socket.on('available', function (status) {
        console.log('got status from server which is:'+ status);
        available=status;
        console.log("inside the socket.on"+available);
        console.log('leaving test, do you see any got status above?');

        callback(); <-- CALL YOUR CALLBACK FUNCTION HERE
    });
}

然后更改您的getstream函数，以便它将一个回调传递给testAvailability，并将函数的其余部分移动到该回调中：

function getstream() {

    console.log('calling testAvail, Avail value is:' + available);
    testAvailability(function() {
        console.log('Available:'+available);
        if (available || SelfSharing) {

             // Do something
             setDefaults();
        }
    });
}

有几件事要注意：

1. getstream现在是异步的。如果有其他东西在等待它完成，则需要对其进行更改，以便它也接受一个回调函数。
2. 我看到您正在socket的error事件中进行某种重试。在这种情况下，这可能是可以的，这取决于您的应用程序，但通常情况下，当发生错误时，您希望将错误作为回调的第一个参数。

Answer 2

我们开始：

function getstream() {

    console.log('calling testAvail, Avail value is:' + available);
    testAvailability(function(available){
        console.log('Available:'+available);
        if (available || SelfSharing) {

             // Do something
             setDefaults();

             return;
        }
    });
}

function testAvailability(callback) {
    console.log('entered test');
    var stat;
    var socket = io.connect('http://somedomain.com');
    socket.on('error', function() {

        console.log('There was an error at server end please try again');
        // chrome.runtime.reload();

        setTimeout(chrome.runtime.reload(),3000);
        //here i change options
        //socket = io.connect(host, options);

        callback(false);
    });
    socket.emit('available');
    socket.on('available', function (status) {
        console.log('got status from server which is:'+ status);
        console.log('leaving test, do you see any got status above?');
        callback(true);
    });
}