semaphore即信号量，Open-falcon在将queue中的数据发送给graph时，用semaphore管制并发的goroutine数量，防止产生大量的发送goroutine。

func forward2GraphTask(Q *list.SafeListLimited, node string, addr string, concurrent int) {    sema := nsema.NewSemaphore(concurrent)    for {        items := Q.PopBackBy(batch)        sema.Acquire()        go func(addr string, graphItems []*cmodel.GraphItem, count int) {            defer sema.Release()            err = GraphConnPools.Call(addr, "Graph.Send", graphItems, resp)            ....        }        ....    }}

semaphore应用channel实现：

  • 定义一个len的channel；
  • 当申请semaphore时，入队channel一个元素，当超过len时，阻塞住，也就是申请失败；
  • 当开释semaphore是，出队channel一个元素；
type Semaphore struct {   bufSize int   channel chan int8}func NewSemaphore(concurrencyNum int) *Semaphore {   return &Semaphore{channel: make(chan int8, concurrencyNum), bufSize: concurrencyNum}}

申请semaphore:

//channel入队胜利，返回true；否则返回false；func (this *Semaphore) TryAcquire() bool {   select {   case this.channel <- int8(0):      return true   default:      return false   }}//若channel未满，入队返回；否则，阻塞func (this *Semaphore) Acquire() {   this.channel <- int8(0)}

开释semaphore: channel出队一个元素

func (this *Semaphore) Release() {   <-this.channel}

查问可用的semaphore:

func (this *Semaphore) AvailablePermits() int {   return this.bufSize - len(this.channel)}