Question

当使用不依赖于async库的第三方库时，以某种方式处理结果回调中的错误会调用其中一个并行任务中的任意回调。

例如

var async = require('async'),
    bloomjs = require('bloom-js');
var client = new bloomjs.Client({url: "http://localhost:3005/api"});

async.parallel([function (cb) {
  console.log('callback1');
  client.find('usgov.hhs.npi', '1558490003', function (err, results) {
    console.log('callback2');
    if (err) return cb(err);
    cb(results);
  });
}], function (err, results) {
  console.log('callback3');
  throw "hello";
  if(err) return console.dir(err);
  console.dir(results);
});

生成输出

callback1
callback2
callback3
callback2

/Users/untoldone/Source/async-demo/node_modules/async/lib/async.js:30
            if (called) throw new Error("Callback was already called.");
                              ^
Error: Callback was already called.
    at /Users/untoldone/Source/async-demo/node_modules/async/lib/async.js:30:31
    at /Users/untoldone/Source/async-demo/node_modules/async/lib/async.js:251:21
    at /Users/untoldone/Source/async-demo/node_modules/async/lib/async.js:575:34
    at /Users/untoldone/Source/async-demo/demo.js:9:21
    at /Users/untoldone/Source/async-demo/node_modules/bloom-js/src/bloom.js:117:18
    at IncomingMessage.<anonymous> (/Users/untoldone/Source/async-demo/node_modules/bloom-js/src/bloom.js:219:22)
    at IncomingMessage.EventEmitter.emit (events.js:117:20)
    at _stream_readable.js:920:16
    at process._tickCallback (node.js:415:13)

似乎callback2以某种方式用于处理callback3中的异常。但鉴于bloomjs永远不会使用async库，我不知道这是怎么回事。想法？

Answer 1

我怀疑在bloomjs.Client.find内部，回调代码包含如下内容：

try {
    callback(false, result);
} catch (e) {
    callback(e, result);
}

因此，当您的回调引发hello错误时，上述代码会捕获此错误，并重新调用client.find回调。这将再次调用cb()，但async.js检测到此循环并发出自己的错误信号。

Javascript Async并行调用不相关的回调

1 个答案: