在javascript中查看所有待处理的承诺 [英] View all pending promises in javascript

问题描述

在我的测试中，有时我会得到超时，看看超时之前待处理的承诺在哪里是非常有用的，这样我就知道哪些承诺最有可能处于始终待定状态 。

In my tests, sometimes I get timeouts, and it would be very useful to see what where the promises that were pending before the timeout, so that I know what promises have the most chances of being in an "always pending state".

有没有办法做到这一点？

Is there a way to do that ?

这是一个示例代码：

Promise.resolve().then(function firstFunction() {
    console.log(1);
    return 1;
}).then(function () {
    return new Promise(function secondFunction(resolve, reject) {
        // NEVER RESOLVING PROMISE
        console.log(2);
    });
}).then(function thirdFunction() {
    // function that will never be called
    console.log(3);
})

setTimeout(function timeoutTest() {
    const pendingPromises = [];// ??????????? how do I get the pendingPromises
    console.log(pendingPromises);
    process.exit();
}, 5000);

我希望，如果可能的话，进入 pendingPromises 函数的名称和承诺的堆栈跟踪 secondFunction ，因为它是永远无法解析的函数。

I would like, if possible, to get in pendingPromises the name of the function and stacktrace of the promise secondFunction, since it is the one that will never resolve.

推荐答案

承诺链是逐步设计的，以便在其成功路径或其错误路径下的原因中提供价值。它不是设计用于在某个任意时间点查询快照被其同化的个人承诺的状态。

A promise chain is designed progressively to deliver values down its success path or a "reason" down its error path. It is not designed to be enquired at some arbitrary point in time for a "snapshot" the state of individual promises that are assimilated by it.

因此，承诺链没有自然的方式来做你所要求的。

Therefore, a promise chain offers no "natural" way to do what you ask.

你需要设计机制：

• 注册感兴趣的承诺。


• 跟踪每个已注册承诺的状态（如果承诺实施尚未提供）。


• 按要求退回已注册的承诺，按州过滤。

沿着这些行的构造函数将完成这项工作：

A constructor along these lines will do the job :

function Inspector() {
    var arr = [];
    this.add = function(p, label) {
        p.label = label || '';
        if(!p.state) {
            p.state = 'pending';
            p.then(
                function(val) { p.state = 'resolved'; },
                function(e) { p.state = 'rejected'; }
            );
        }
        arr.push(p);
        return p;
    };
    this.getPending  = function() {
        return arr.filter(function(p) { return p.state === 'pending'; });
    };
    this.getSettled = function() {
        return arr.filter(function(p) { return p.state !== 'pending'; });
    };
    this.getResolved = function() {
        return arr.filter(function(p) { return p.state === 'resolved'; });
    };
    this.getRejected = function() {
        return arr.filter(function(p) { return p.state === 'rejected'; });
    };
    this.getAll  = function() {
        return arr.slice(0); // return a copy of arr, not arr itself.
    };
};

问题所需的唯一方法是 .add（） 和 .getPending（）。其他是完整性。

The only methods required by the question are .add() and .getPending(). The others are provided for completeness.

您现在可以写：

var inspector = new Inspector();

Promise.resolve().then(function() {
    console.log(1);
}).then(function() {
    var p = new Promise(function(resolve, reject) {
        // NEVER RESOLVING PROMISE
        console.log(2);
    });
    return inspector.add(p, '2');
}).then(function() {
    // function that will never be called
    console.log(3);
});

setTimeout(function() {
    const pendingPromises = inspector.getPending();
    console.log(pendingPromises);
    process.exit();
}, 5000);

小提琴

fiddle

使用 Inspector 并不局限于承诺链同化的承诺。它可以用于任意一组承诺，例如一个集合与 Promise.all（）：

The use of Inspector isn't confined to promises assimilated by promise chains. It could be used for any arbitrary set of promises, for example a set to be aggregated with Promise.all() :

promise_1 = ...;
promise_2 = ...;
promise_3 = ...;

var inspector = new Inspector();
inspector.add(promise_1, 'promise 1');
inspector.add(promise_2, 'promise 2');
inspector.add(promise_3, 'promise 3');

var start = Date.now();
var intervalRef = setInterval(function() {
    console.log(Date.now() - start + ': ' + inspector.getSettled().length + ' of ' + inspector.getAll().length + ' promises have settled');
}, 50);

Promise.all(inspector.getAll()).then(successHandler).catch(errorHandler).finally(function() {
    clearInterval(intervalRef);
});

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