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Asynchronous concurrent requests are executed sequentially

I start the server using Node.js and I need to request data from another server that I run ( localhost:3001). I need to make a lot of requests (~ 200) to the data server and collect the data (response sizes vary from ~ 20 Kb to ~ 20 Mb). Each request is independent, and I would like to save the answers as one giant array of forms:

[{"urlAAA": responseAAA}, {"urlCCC": responseCCC}, {"urlBBB": responseBBB}, etc ]

Note that the order of the elements does not matter; they should ideally fill the array in the order in which data becomes available.

var express = require('express');
var router = express.Router();
var async = require("async");
var papa = require("papaparse");
var sync_request = require('sync-request');
var request = require("request");

var pinnacle_data = {};
var lookup_list = [];
for (var i = 0; i < 20; i++) {
    lookup_list.push(i);
}

function write_delayed_files(object, key, value) {
    object[key] = value;
    return;
}

var show_file = function (file_number) {
    var file_index = Math.round(Math.random() * 495) + 1;
    var pinnacle_file_index = 'http://localhost:3001/generate?file=' + file_index.toString();
    var response_json = sync_request('GET', pinnacle_file_index);
    var pinnacle_json = JSON.parse(response_json.getBody('utf8'));
    var object_key = "file_" + file_number.toString();
    pinnacle_data[object_key] = pinnacle_json;
    console.log("We've handled file:    " + file_number);
    return;
};

async.each(lookup_list, show_file, function (err) {});



console.log(pinnacle_data);

/* GET contact us page. */
router.get('/', function (req, res, next) {
    res.render('predictionsWtaLinks', {title: 'Async Trial'});
});

module.exports = router;

Now that this program is running, it displays:

We've handled file:    0
We've handled file:    1
We've handled file:    2
We've handled file:    3
We've handled file:    4
We've handled file:    5
etc

, , , "", , , , , async.each(). 1-2 , .

, , :

var response_json = sync_request('GET', pinnacle_file_index);

-

request(pinnacle_file_index, function (error, response, body) {
    if (!error && response.statusCode == 200) {
        pinnacle_data[object_key] = JSON.parse(body);
    }
});

.

, :

  • URL- async.parallel(function_list, function (err, results) { //add results to pinnacle_data[]});. ( , ).

, :

-

( ~ 80 , npm requestretry). , ~ 80 5 , 1000.

var performance = require("performance-now");
var time_start = performance();
var async = require("async");
var request_retry = require('requestretry');

var lookup_list = [];
var total_requests = 50;
for (var i = 0; i < total_requests; i++) {
    lookup_list.push(i);
}

var pinnacle_data = {};
async.map(lookup_list, function (item, callback) {
        var file_index = Math.round(Math.random() * 495) + 1;
        var pinnacle_file_index = 'http://localhost:3001/generate?file=' + file_index;
        request_retry({
                url: pinnacle_file_index,
                maxAttempts: 20,
                retryDelay: 20,
                retryStrategy: request_retry.RetryStrategies.HTTPOrNetworkError
            },
            function (error, response, body) {
                if (!error && response.statusCode == 200) {
                    body = JSON.parse(body);
                    var data_array = {};
                    data_array[file_index.toString()] = body;
                    callback(null, data_array);
                } else {
                    console.log(error);
                    callback(error || response.statusCode);
                }
            });
    },
    function (err, results) {
        var time_finish = performance();
        console.log("It took " + (time_finish - time_start).toFixed(3) + "ms to complete " + total_requests + " requests.");
        console.log("This gives an average rate of " + ((time_finish - time_start) / total_requests).toFixed(3) + " ms/request");
        if (!err) {
            for (var i = 0; i < results.length; i++) {
                for (key in results[i]) {
                    pinnacle_data[key] = results[i][key];
                }
            }
            var length_array = Object.keys(pinnacle_data).length.toString();
            console.log("We've got all the data, totalling " + length_array + " unique entries.");
        } else {
            console.log("We had an error somewhere.");
        }
    });

.

+4
3

, async.parallel() , . , - node.js , . , async.parallel() ( async) .

, async.map(). async.map(), , , , , , :

var async = require("async");
var request = require("request");

// create list of URLs
var lookup_list = [];
for (var i = 0; i < 20; i++) {
    var index = Math.round(Math.random() * 495) + 1;
    var url = 'http://localhost:3001/generate?file=' + index;
    lookup_list.push(url);
}

async.map(lookup_list, function(url, callback) {
    // iterator function
    request(url, function (error, response, body) {
        if (!error && response.statusCode == 200) {
            var body = JSON.parse(body);
            // do any further processing of the data here
            callback(null, body);
        } else {
            callback(error || response.statusCode);
        }
    });
}, function(err, results) {
    // completion function
    if (!err) {
        // process all results in the array here
        console.log(results);
        for (var i = 0; i < results.length; i++) {
            // do something with results[i]
        }
    } else {
        // handle error here
    }
});

Bluebird promises Promise.map() :

var Promise = require("bluebird");
var request = Promise.promisifyAll(require("request"), {multiArgs: true});

// create list of URLs
var lookup_list = [];
for (var i = 0; i < 20; i++) {
    var index = Math.round(Math.random() * 495) + 1;
    var url = 'http://localhost:3001/generate?file=' + index;
    lookup_list.push(url);
}

Promise.map(lookup_list, function(url) {
    return request.getAsync(url).spread(function(response, body) {
        if response.statusCode !== 200) {
            throw response.statusCode;
        }
        return JSON.parse(body);
    });
}).then(function(results) {
    console.log(results);
    for (var i = 0; i < results.length; i++) {
        // process results[i] here
    }
}, function(err) {
    // process error here
});
+5

, URL- . :

var request = require('request');
var async = require('async');

var urls = ['http://microsoft.com', 'http://yahoo.com', 'http://google.com', 'http://amazon.com'];

var loaders = urls.map( function(url) {
  return function(callback) {
        request(url, callback);
  }
});

async.parallel(loaders, function(err, results) {
        if (err) throw(err); // ... handle appropriately
        // results will be an array of the results, in 
        // the same order as 'urls', even thought the operation
        // was done in parallel
        console.log(results.length); // == urls.length
});

, async.map:

var request = require('request');
var async = require('async');

var urls = ['http://microsoft.com', 'http://yahoo.com', 'http://google.com', 'http://amazon.com'];

async.map(urls, request, function(err, results) {
        if (err) throw(err);          // handle error 
        console.log(results.length);  // == urls.length
});
+4

Try the following:

var async = require("async");
var request = require("request");
var show_file = function (file_number,cb) {
    //..Sync ops
     var file_index = Math.round(Math.random() * 495) + 1;
     var pinnacle_file_index = 'http://localhost:3001/generate?file='+file_index.toString();
    //request instance from Request npm Module
    //..Async op --> this should make async.each asynchronous
    request(pinnacle_file_index, function (error, response, body) {
       if(error)
           return cb(error);
       var object_key = "file_" + file_number.toString();
      pinnacle_data[object_key] = JSON.parse(body);
      return cb();
    });
};

async.each(
  lookup_list, 
  show_file,
  function (err) {
    if(err){
       console.log("Error",err);
    }else{
       console.log("Its ok");
       console.log(pinnacle_data);
   }
});
0
source

Source: https://habr.com/ru/post/1606284/

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