I want to know how parallel execution works in async.js
async = require('async')
async.parallel([
function(callback){
for (var i = 0; i < 1000000000; i++) /* Do nothing */;
console.log("function: 1")
},
function(callback){
console.log("function: 2")
}
]);
In the above example, I expect obtain the output:
function: 2
function: 1
but, the console throws the inverse, what is happening? thanks.
You get the answer you don't expect because async
launches function: 1
first and it doesn't release control back to the event loop. You have no async functions in function: 1
.
Node.js is a single-threaded asynchronous server. If you block the event loop with a long running CPU task then no other functions can be called until your long running CPU task finishes.
Instead for a big for loop, try making http requests. For example...
async = require('async')
request = require('request')
async.parallel([
function(callback){
request("http://google.jp", function(err, response, body) {
if(err) { console.log(err); callback(true); return; }
console.log("function: 1")
callback(false);
});
},
function(callback){
request("http://google.com", function(err, response, body) {
if(err) { console.log(err); callback(true); return; }
console.log("function: 2")
callback(false);
});
}
]);
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With