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balancer.go
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balancer.go
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package rio
import (
"container/heap"
"fmt"
"log"
"time"
)
// The balancer struct, this struct is used inside the GetBalancer method to provide a load balancer to the caller
type Balancer struct {
// Its the pool of Worker, which is itself a priority queue based on min heap.
pool Pool
// This channel is used to receive a request instance form the caller. After getting the request it is dispatched
// to the most lightly loaded worker
jobChannel chan *Request
// This channel is used by the worker. After processing a task, a worker uses this channel to let the balancer know
// that it is done and able to take new requests from its request channel
done chan *Worker
// Its the number of queued requests
queuedItems int
// The close channel. When the Close method is called by any calling goroutine sending a chanel of boolean, the
// balancer waits for all the requests to be processed, then closes all the worker, closes all its owen loops and
// then finally respond by sending boolean true to the passed channel by the caller, confirming that all the inner
// loop are closed and the balancer is shutdown.
closeChannel chan chan bool
}
// Use this method to create an instance of the balancer/load balancer. This method must be created only one, per
// the go runtime as it is very much resource intensive.
func GetBalancer(workerCount, taskPerWorker int) *Balancer {
b := &Balancer{
done: make(chan *Worker),
jobChannel: make(chan *Request),
closeChannel: make(chan chan bool),
}
p := make([]*Worker, workerCount)
for i := 0; i < workerCount; i++ {
w := &Worker{
requests: make(chan *Request, taskPerWorker),
pending: 0,
index: i,
Name: fmt.Sprintf("Worker-%d", i),
done: b.done,
closeChannel: make(chan chan bool),
}
p[i] = w
w.Run()
}
b.pool = p
b.balance()
return b
}
// Use this method from the caller side to queue a new job/request. It will be validated and if found proper, will be
// passed to the worker to be processed. This method returns immediately
func (b *Balancer) PostJob(job *Request) error {
err := job.Validate()
if err == nil {
b.jobChannel <- job
return nil
}
return err
}
// Use this method to close/shutdown a balancer. When this is called, balancer waits for all the requests to be
// processed, then closes all the worker, closes all its owen loops and then finally respond by sending boolean true
// to the passed channel by the caller, confirming that all the inner loop are closed and the balancer is shutdown.
// Once shutdown, sending a request to it will raise a panic
func (b *Balancer) Close(cb chan bool) {
b.closeChannel <- cb
}
// Unexported method. Only used by the balancer to managed the posted requests.
func (b *Balancer) balance() {
go func() {
for {
select {
case req := <-b.jobChannel:
b.dispatch(req)
b.queuedItems++
case w := <-b.done:
b.completed(w)
b.queuedItems--
case cb := <-b.closeChannel:
if b.queuedItems > 0 {
time.AfterFunc(1*time.Second, func() { b.closeChannel <- cb })
} else {
for _, w := range b.pool {
c := make(chan bool)
w.Close(c)
<-c
fmt.Println("")
}
cb <- true
log.Println("Closing balancer")
return
}
}
}
}()
}
// Balancer uses this method to send a validated request to the most lightly loaded worker
func (b *Balancer) dispatch(req *Request) {
w := heap.Pop(&b.pool).(*Worker)
log.Println(fmt.Sprintf("Dispatching request to [%s]", w.Name))
w.DoWork(req)
w.pending++
heap.Push(&b.pool, w)
}
// Worker when completes a task return to the balancer and its pending count is decreased by 1
func (b *Balancer) completed(w *Worker) {
w.pending--
worker := heap.Remove(&b.pool, w.index)
heap.Push(&b.pool, worker)
}