AWS SQS Node.js script does not await

Question

Trying to send several messages (from AWS SQS lambda, if that matters) but it's never waiting for the promises.

function getEndpoint(settings){
    return new Promise(function(resolve, reject) { 
    // [...] more stuff here
}

Which is then called in a loop:

exports.handler = async (event) => {
    var messages = [];
    event.Records.forEach(function(messageId, body) {
        //options object created from some stuff
        messages.push(getEndpoint(options).then(function(response){
            console.log("anything at all"); //NEVER LOGGED
        }));
    });
    await Promise.all(messages);
};

But the await seems to be flat out skipped. I'm not sure how I'm getting Process exited before completing request with an explicit await. I have similar async await/promise setups in other scripts that work, but cannot spot what I've done wrong with this one.

Answer 1

你忘了向 lambda 返回一些东西：

exports.handler = async (event) => {
    var messages = [];
    event.Records.forEach(function(messageId, body) {
        //options object created from some stuff
        messages.push(getEndpoint(options));
    });
    await Promise.all(messages);
    return 'OK'
};

这也应该有效：

exports.handler = (event) => { // async is not mandatory here
    var messages = [];
    event.Records.forEach(function(messageId, body) {
        //options object created from some stuff
        messages.push(getEndpoint(options));
    });
    return Promise.all(messages); // returning a promise
};

你可以使用地图：

exports.handler = (event) => { // async is not mandatory here
    const messages = event.Records.map(function(messageId, body) {
        //options object created from some stuff
        return getEndpoint(options)
    });
    return Promise.all(messages); // returning a promise
};

要理解为什么会发生这种情况，您必须深入了解 lambda 的实现：它本质上将等待函数堆栈被清除，并且由于您根本没有在其中返回任何内容，因此函数堆栈在将所有内容排队后立即变空- 在await调用后添加一个简单的 return使 fn 堆栈不为空，这意味着 lambda 将等待它完成。

如果您在标准节点上运行它，您的函数也会在承诺完成之前返回，但您的节点进程在堆栈被清除之前不会退出。这是 lambda 与股票节点不同的地方。