webworker-threads/examples/ex05_pool.md

Lightweight Web Worker API implementation with native threads

## Using the thread pool

Our previous examples used a single worker thread, and thus only one processor core.
If we want to take full advantage of multi-core processors, we need the ability to delegate
expensive computations to a pool of theads. This example demonstrates the pool thread that comes
bundled with webworker-threads.

First, we create a pool

``` javascript
var Threads = require('webworker-threads');
var pool = Threads.createPool(3);
```


Then we load our fibonacci function in all the pool's threads:

``` javascript
function fibo(n) {
	return n > 1 ? fibo(n - 1) + fibo(n - 2) : 1;
}

pool.all.eval(fibo);
```

Now, we can get fibonacci numbers from our pool

We request them in reverse order, to show that longer computations (`fibo(40)`) run in 
parallel with shorter ones (`fibo(39)`, `fibo(38)`, ...). The results won't come out in strictly decreasing order.

``` javascript
var remain = 11;
for (var i = 40; i >= 30; i--) {
	// extra closure to get proper scoping on 'i'
	(function(i) {
		// dispatch each request to the first available thread
		pool.any.eval('fibo(' + i + ')', function(err, val) {
			console.log('fibo(' + i + ')=' + i);
			// destroy the pool when all results have been produced
			if (--remain == 0) console.log('bye!'), pool.destroy();
		});
	})(i);
}
```

### Typical (*) Output

(*) Execution is non-deterministic. So order may vary.

```
fibo(38)=38
fibo(39)=39
fibo(37)=37
fibo(35)=35
fibo(36)=36
fibo(33)=33
fibo(34)=34
fibo(31)=31
fibo(32)=32
fibo(30)=30
fibo(40)=40
bye!
```