会做一些释放资源的操作 if sg := c.sendq.dequeue(); sg != nil {
recv(c, sg, ep, func() { unlock(&c.lock) }, 3)
return true, true
}
func recv(c *hchan, sg *sudog, ep unsafe.Pointer, unlockf func(), skip int) {
if c.dataqsiz == 0 {
if raceenabled {
racesync(c, sg)
}
if ep != nil {
// 如果无缓存，直接从发送者拷贝数据
recvDirect(c.elemtype, sg, ep)
}
} else {
// 由于队列已满，接收数据的索引和发送数据的索引一致
qp := chanbuf(c, c.recvx)
if raceenabled {
racenotify(c, c.recvx, nil)
racenotify(c, c.recvx, sg)
}
// 数据从队列拷贝到目标内存地址
if ep != nil {
typedmemmove(c.elemtype, ep, qp)
}
// 数据从发送者拷贝到缓冲区
typedmemmove(c.elemtype, qp, sg.elem)
c.recvx++
if c.recvx == c.dataqsiz {
c.recvx = 0
}
c.sendx = c.recvx // c.sendx = (c.sendx+1) % c.dataqsiz
}
sg.elem = nil
gp := sg.g
unlockf()
gp.param = unsafe.Pointer(sg)
sg.success = true
if sg.releasetime != 0 {
sg.releasetime = cputicks()
}
// 无论发生哪种情况，运行时都会调用 runtime.goready 将当前处理器的 runnext 设置成发送数据的 Goroutine，在调度器下一次调度时将阻塞的发送方唤醒。
goready(gp, skip+1)
}
当缓冲区存在数据时，从 Channel 的缓冲区中接收数据
if c.qcount > 0 {
// 直接从队列取数据
qp := chanbuf(c, c.recvx)
if raceenabled {
racenotify(c, c.recvx, nil)
}
// 放到目标内存
if ep != nil {
typedmemmove(c.elemtype, ep, qp)
}
// 清空队列中对应的元素
typedmemclr(c.elemtype, qp)
// 接收索引+1
c.recvx++
if c.recvx == c.dataqsiz {
c.recvx = 0
}
// 队列元素-1
c.qcount--
unlock(&c.lock)
return true, true
}
当缓冲区中不存在数据时，等待其他 Goroutine 向 Channel 发送数据
if !block {
unlock(&c.lock)
return false, false
}
// no sender available: block on this channel.
gp := getg()
mysg := acquireSudog()
mysg.releasetime = 0
if t0 != 0 {
mysg.releasetime = -1
}
// No stack splits between assigning elem and enqueuing mysg
// on gp.waiting where copystack can find it.
mysg.elem = ep
mysg.waitlink = nil
gp.waiting = mysg
mysg.g = gp
mysg.isSelect = false
mysg.c = c
gp.param = nil
c.recvq.enqueue(mysg)
// 阻塞等待，让出使用权
atomic.Store8(&gp.parkingOnChan, 1)
gopark(chanparkcommit, unsafe.Pointer(&c.lock), waitReasonChanReceive, traceEvGoBlockRecv, 2)
// 唤醒之后清空sudog
if mysg != gp.waiting {
throw("G waiting list is corrupted")
}
gp.waiting = nil
gp.activeStackChans = false
if mysg.releasetime > 0 {
blockevent(mysg.releasetime-t0, 2)
}
success := mysg.success
gp.param = nil
mysg.c = nil
releaseSudog(mysg)
return true, success
关闭channel
-
当 Channel 是一个空指针或者已经被关闭时，Go 语言运行时都会直接崩溃并抛出异常
func closechan(c *hchan) {
if c == nil {
panic(plainError("close of nil channel"))
}
lock(&c.lock)
if c.closed != 0 {
unlock(&c.lock)
panic(plainError("close of closed channel"))
}
-
将 recvq 和 sendq 两个队列中的数据加入到 Goroutine 列表 gList 中，与此同时该函数会清除所有 runtime.sudog 上未被处理的元素
c.closed = 1
var glist gList
// release all readers
for {
sg := c.recvq.dequeue()
if sg == nil {
break
}
if sg.elem != nil {
typedmemclr(c.elemtype, sg.elem)
sg.elem = nil
}
if sg.releasetime != 0 {
sg.releasetime = cputicks()
}
gp := sg.g
gp.param = unsafe.Pointer(sg)
sg.success = false
if raceenabled {
raceacquireg(gp, c.raceaddr())
}
glist.push(gp)
}
// release all writers (they will panic)
for {
sg := c.sendq.dequeue()
if sg == nil {
break
}
sg.elem = nil
if sg.releasetime != 0 {
sg.r