2012/waza/load2

type Request struct {
    fn func() int  // The operation to perform.
    c  chan int    // The channel to return the result.
}

func requester(work chan<- Request) {
    c := make(chan int)
    for {
    	// Kill some time (fake load).
        Sleep(rand.Int63n(nWorker * 2 * Second))
        work <- Request{workFn, c} // send request
        result := <-c              // wait for answer
        furtherProcess(result)  
	}	
}

func (w *Worker) work(done chan *Worker) {
    for {
        req := <-w.requests // get Request from balancer
        req.c <- req.fn()   // call fn and send result
        done <- w           // we've finished this request
    }
}

type Pool []*Worker

type Balancer struct {
	pool Pool
	done chan *Worker
}

func (b *Balancer) balance(work chan Request) {
    for {
        select {
        case req := <-work: // received a Request...
            b.dispatch(req) // ...so send it to a Worker
        case w := <-b.done: // a worker has finished ...
            b.completed(w)  // ...so update its info
        }
    }
}
func (p Pool) Less(i, j int) bool {
    return p[i].pending < p[j].pending
}

type Worker struct {
    requests chan Request // work to do (buffered channel)
    pending  int          // count of pending tasks
    index     int         // index in the heap
}

// Send Request to worker
func (b *Balancer) dispatch(req Request) {
	// Grab the least loaded worker...
    w := heap.Pop(&b.pool).(*Worker)
    // ...send it the task.
    w.requests <- req
    // One more in its work queue.
    w.pending++
    // Put it into its place on the heap.
    heap.Push(&b.pool, w)
}

// Job is complete; update heap
func (b *Balancer) completed(w *Worker) {
	// One fewer in the queue.
	w.pending--
	// Remove it from heap.                  
	heap.Remove(&b.pool, w.index)
    // Put it into its place on the heap.
	heap.Push(&b.pool, w)
}

func (p Pool) Less(i, j int) bool {
   return p[i].pending < p[j].pending
}