webworker-threads/examples/ex03_ping_pong.js

Lightweight Web Worker API implementation with native threads

/// !example
/// ## Sending events both ways between the main thread and a worker thread
/// 
/// This third example demonstrates how we can use events to communicate in both directions
/// between main thread and worker thread.
/// 
/// Like before, we create a worker thread and we define the fibonacci function:
var Threads = require('webworker-threads');
var t = Threads.create();

function fibo(n) {
	return n > 1 ? fibo(n - 1) + fibo(n - 2) : 1;
}
/// In the previous example we were running a loop that generates fibonacci numbers in the worker thread.  
/// This is fine if the generator produces the number at a slower rate than the main thread can consume them 
/// but it will hog memory if the main thread is too busy and cannot consume the data events fast enough.  
/// We can improve this by controlling the flow with events in both directions.
/// 
/// The `thread` global variable that **webworker-threads** predefines in every worker thread is also an `EventEmitter`.  
/// So we will use it to send events in the other direction, from the main thread to the worker thread.
/// 
/// Our modified generator does not use a loop any more. Instead, it generates numbers in response to `next` events
/// sent from the main thread. Here is the new generator:
function generateFibos() {
	var i = 1;
	thread.on('next', function() {
		thread.emit('data', i, fibo(i));
		i++;
	});
}
/// From the main thread, we listen for the `data` events emitted by the worker thread.  
/// Every time we get a `data` event from the worker thread, we print the result and we `emit` a 
/// `next` event into the worker thread (stopping at 40): 
t.on('data', function(n, result) {
	console.log('fibo(' + n + ') = ' + result);
	if (n < 40) t.emit('next');
	else console.log('bye!'), t.destroy();
});
/// We now have all we need for our little ping-pong game. We load the two functions into the thread:
t.eval(fibo);
t.eval(generateFibos);
/// We start the generator in the worker thread:
t.eval("generateFibos()");
/// And we start the game by emitting the first `next` event:
t.emit('next');
/// ### Output
/// 
/// ```
/// fibo(1) = 1
/// fibo(2) = 2
/// fibo(3) = 3
/// fibo(4) = 5
/// ...
/// fibo(39) = 102334155
/// fibo(40) = 165580141
/// bye!
/// ```