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| package main | |
| import ( | |
| "container/heap" | |
| "fmt" | |
| "time" | |
| "math/rand" | |
| ) | |
| func main() { | |
| work := make(chan Request) | |
| bal := new(Balancer) | |
| bal.done = make(chan *Worker) | |
| for i := 0; i < 10; i++ { | |
| worker := new(Worker) | |
| worker.requests = make(chan Request) | |
| worker.index = i | |
| bal.pool = append(bal.pool, worker) | |
| } | |
| go requester(work) | |
| bal.balance(work) | |
| } | |
| func requester(work chan Request) { | |
| for { | |
| response := make(chan string) | |
| // Kill some time (fake load). | |
| time.Sleep(10 * time.Millisecond) | |
| work <- Request{doWork, response} // send request | |
| go func(response chan string) { | |
| fmt.Println(<-response) | |
| }(response) | |
| } | |
| } | |
| 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 | |
| } | |
| } | |
| } | |
| // Send Request to worker | |
| func (b *Balancer) dispatch(req Request) { | |
| w := heap.Pop(&b.pool).(*Worker) | |
| go w.work(b.done) | |
| // ...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 (w *Worker) work(done chan *Worker) { | |
| for { | |
| req := <- w.requests // get Request from balancer | |
| req.response <- req.fn(*w) // call fn and send result | |
| done <- w // we've finished this request | |
| } | |
| } | |
| func doWork(worker Worker) string { | |
| time.Sleep(time.Duration(rand.Intn(1000)) * time.Millisecond) | |
| return fmt.Sprintf("index: %d pending:%d", worker.index, worker.pending) | |
| } | |
| type Request struct { | |
| fn func(worker Worker) string | |
| response chan string | |
| } | |
| type Worker struct { | |
| requests chan Request // work to do (buffered channel) | |
| pending int // count of pending tasks | |
| index int // index in heap | |
| } | |
| type Balancer struct { | |
| pool Pool | |
| done chan *Worker | |
| } | |
| type Pool []*Worker | |
| func (p Pool) Len() int { return len(p) } | |
| func (p Pool) Less(i, j int) bool { return p[i].pending < p[j].pending } | |
| func (p Pool) Swap(i, j int) { p[i], p[j] = p[j], p[i] } | |
| func (p *Pool) Push(x interface{}) { | |
| *p = append(*p, x.(*Worker)) | |
| } | |
| func (p *Pool) Pop() interface{} { | |
| old := *p | |
| n := len(old) | |
| x := old[n-1] | |
| *p = old[0 : n-1] | |
| return x | |
| } |
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Updated with fixes