目录

channel

2021-01-02 收录于 golang 约 511 字预计阅读 2 分钟

目录

chansend, chanrec, closechan 的结果

黄色标记为返回值

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// chanrecv 有两个 bool 返回值 selected received
// 例如:
// select {
// case v, ok =<- c:
//    ...
// }
// selected : 表示 case 可以被 selected 
// received : ok == true
func chanrecv(c *hchan, ep unsafe.Pointer, block bool) (selected, received bool) {}

block : blocking IO, 取决于是否有 default case

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  func full(c *hchan) bool {
      if c.dataqsiz == 0 {
          return c.recvq.first == nil
      }
      return c.qcount == c.dataqsiz
  }

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  func empty(c *hchan) bool {
      if c.dataqsiz == 0 {
          return atomic.Loadp(unsafe.Pointer(&c.sendq.first)) == nil
      }
      return atomic.Loaduint(&c.qcount) == 0
  }

源码

runtime/chan.go

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type hchan struct {
	qcount   uint           // total data in the queue
	dataqsiz uint           // size of the circular queue
	buf      unsafe.Pointer // points to an array of dataqsiz elements
	elemsize uint16
	closed   uint32
	elemtype *_type // element type
	sendx    uint   // send index
	recvx    uint   // receive index
	recvq    waitq  // list of recv waiters
	sendq    waitq  // list of send waiters

	// 锁
	lock mutex
}

type waitq struct {
	first *sudog
	last  *sudog
}

语法糖

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// compiler implements
//
//	select {
//	case c <- v:
//		... foo
//	default:
//		... bar
//	}
//
// as
//
//	if selectnbsend(c, v) {
//		... foo
//	} else {
//		... bar
//	}
//
func selectnbsend(c *hchan, elem unsafe.Pointer) (selected bool) {
	return chansend(c, elem, false, getcallerpc())
}

// compiler implements
//
//	select {
//	case v = <-c:
//		... foo
//	default:
//		... bar
//	}
//
// as
//
//	if selectnbrecv(&v, c) {
//		... foo
//	} else {
//		... bar
//	}
//
func selectnbrecv(elem unsafe.Pointer, c *hchan) (selected bool) {
	selected, _ = chanrecv(c, elem, false)
	return
}

// compiler implements
//
//	select {
//	case v, ok = <-c:
//		... foo
//	default:
//		... bar
//	}
//
// as
//
//	if c != nil && selectnbrecv2(&v, &ok, c) {
//		... foo
//	} else {
//		... bar
//	}
//
func selectnbrecv2(elem unsafe.Pointer, received *bool, c *hchan) (selected bool) {
	// TODO(khr): just return 2 values from this function, now that it is in Go.
	selected, *received = chanrecv(c, elem, false)
	return
}