How to capture response from child process in nodejs - node.js

Question

I am trying to capture some response from my child process in master process. I can log information of child process in master process but unable to capture some return xyz response .
Here is code for master process:
var express = require('express');
var app = express();
const
fs = require('fs'),
cp = require('child_process');
app.get('/',onRequest );
function onRequest(request, response) {
var express = require('express');
var app = express();
var child= cp.spawn('node' ,['./child_process/block.js'],filestreamCallback);
child.stdout.on('data', function(data) {
console.log('stdout: ==== ' + data);
});
child.stderr.on('data', function(data) {
console.log('stdout: ' + data);
});
child.on('close', function(code) {
console.log('closing code: ' + code);
});
function filestreamCallback() {
response.writeHead(200, {'Content-Type': 'text/plain'});
baflog.info("Reading Stream completed");
response.write('Thanks for Your patience!\n');
response.end();
}
}
app.listen(5000);
console.log('Server started');
Child process : block.js
/*Keep waiting for 10 seconds*/
console.log("Waiting for child Process (block.js) to complete......");
var startTime = new Date().getTime();
while (new Date().getTime() < startTime + 10000);
ret_resp();
var response = {status:'success'};
function ret_resp(){
return response;
}
console.log("Thank You for waiting......");
Like in console i see output as :
stdout====: Waiting for child Process (block.js) to complete......
-punws-sohan
stdout: ==== Thank You for waiting......
I cannot see output for return response statement
Can anyone suggest how to capture response from child process?

Answer 1

First of all, the busy loop uses up unnecessary CPU time. Just use a setTimeout() instead. Example:
setTimeout(function() {
ret_resp();
// ...
}, 10000);
Secondly, you can't expect return to magically write the returned value to the parent process. Try this instead:
// parent.js
var child = cp.fork('./child_process/block.js', [], { silent: true });
child.stdout.on('data', function(data) {
console.log('stdout: ==== ' + data);
});
child.stderr.on('data', function(data) {
console.log('stdout: ' + data);
});
child.on('message', function(msg) {
console.log('message from child: ' + require('util').inspect(msg));
});
child.on('close', function(code) {
console.log('closing code: ' + code);
});
// child.js
console.log('Waiting for child Process (block.js) to complete......');
setTimeout(function() {
var response = {status:'success'};
function ret_resp() {
process.send(response);
}
ret_resp();
console.log('Thank You for waiting......');
}, 10000);