NodeJS eventloop执行顺序

Question

When sending several requests serially, it seems like

• callbacks are executed when all requests are sent.
• requests seems to get added into a queue but not actually getting executed before the loop is done.

Example

var http = require('http');

var i=0;
var postData = [];

while (i++ < 12) {
    var largeObject = [
        'this' + i,
        'that' + i,
        'then' + i
    ];

    postData.push(largeObject);

    if (postData.length >= 2) {
        console.log('request');
        var options = {
            hostname: 'httpbin.org',
            port: 80,
            path: '/post',
            method: 'POST',
            headers: {
                'Content-Type': 'application/json',
            }
        };
        var req = http.request(options, function(res) {
            console.log(res.statusCode);
            res.on('data', function(chunk) {
                console.log(chunk.toString());
            });

            res.on('end', function() {
                console.log('finished reading response');
            });
        });
        req.end(JSON.stringify(postData), function() {
            console.log('request stream finished');
        });

        postData = [];
    }
}

The output here would look like

request
request
request
request
request
request
request stream finished
request stream finished
request stream finished
request stream finished
request stream finished
request stream finished
200
{
  "args": {}, 
  "data": "[[\"this7\",\"that7\",\"then7\"],[\"this8\",\"that8\",\"then8\"]]", 
  "files": {}, 
  "form": {}, 
  "headers": {
    "Content-Length": "53", 
    "Content-Type": "application/json", 
    "Host": "httpbin.org"
  }, 
  "json": [
    [
      "this7", 
      "that7", 
      "then7"
    ], 
    [
      "this8", 
      "that8", 
      "then8"
    ]
  ], 
  "origin": "xxxxx", 
  "url": "http://httpbin.org/post"
}

finished reading response
200
{
  "args": {}, 
  "data": "[[\"this1\",\"that1\",\"then1\"],[\"this2\",\"that2\",\"then2\"]]", 
  "files": {}, 
  "form": {}, 
  "headers": {
    "Content-Length": "53", 
    "Content-Type": "application/json", 
    "Host": "httpbin.org"
  }, 
  "json": [
    [
      "this1", 
      "that1", 
      "then1"
    ], 
    [
      "this2", 
      "that2", 
      "then2"
    ]
  ], 
  "origin": "xxxx", 
  "url": "http://httpbin.org/post"
}
...

Is there any way to finish one request before the next one is getting executed?

I don't really care about the order, it's more about memory - I'd like to get rid of large objects I am posting

eg

request1
response1
request2
response2
request3
response3
request4
request5
response5
response4

would be absolutely fine. Any suggestion?

Answer 1

Of course, just use some control-flow modules like async or bluebird.

As you don't care about order, I'd advise you to use either async#parallel or bluebird#map . The bluebird#map has a concurrency argument, which can be nice when you need some more control over loops and their amount (so does async#parallelLimit ).

If this doesn't seem straightforward, please comment and I'll add an example.