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
    lock mutex
}

// 無(wú)緩沖通道
ch1 := make(chan int)
// 有緩沖通道
ch2 := make(chan int, 10)

func makechan(t *chantype, size int) *hchan {
   elem := t.elem
    
   // mem：緩沖區(qū)大小 
   mem, overflow := math.MulUintptr(elem.size, uintptr(size))
   if overflow || mem > maxAlloc-hchanSize || size < 0 {
      panic(plainError( "makechan: size out of range" ))
   }

   var c *hchan
   switch {
   // 緩沖區(qū)大小為空，只申請(qǐng)hchanSize大小的內(nèi)存
   case mem == 0:
       c = (*hchan)(mallocgc(hchanSize, nil, true))
       c.buf = c.raceaddr()
   // 元素類(lèi)型不包含指針，一次性分配hchanSize+mem大小的內(nèi)存
   case elem.ptrdata == 0:
       c = (*hchan)(mallocgc(hchanSize+mem, nil, true))
       c.buf = add(unsafe.Pointer(c), hchanSize)
   // 否則就是帶緩存，且有指針，分配兩次內(nèi)存
   default:
      // Elements contain pointers.
       c = new(hchan)
       c.buf = mallocgc(mem, elem, true)
   }
    
   // 保存元素類(lèi)型，元素大小，容量
   c.elemsize = uint16(elem.size)
   c.elemtype = elem
   c.dataqsiz = uint(size)
   lockInit(&c.lock, lockRankHchan)
   
   return c
}

ch <- 3

func chansend(c *hchan, ep unsafe.Pointer, block bool, callerpc uintptr) bool {
   // 如果channel是空
   if c == nil {
      // 非阻塞，直接返回
      if !block {
         return  false
      }
      // 否則阻塞當(dāng)前協(xié)程
      gopark(nil, nil, waitReasonChanSendNilChan, traceEvGoStop, 2)
      throw( "unreachable" )
   }

   // 非阻塞，沒(méi)有關(guān)閉，且容量滿了，無(wú)法發(fā)送，直接返回
   if !block && c.closed == 0 && full(c) {
      return  false
   }

   // 加鎖
   lock(&c.lock)

   // 如果已經(jīng)關(guān)閉，無(wú)法發(fā)送，直接panic
   if c.closed != 0 {
      unlock(&c.lock)
      panic(plainError( "send on closed channel" ))
   }

   // 從接收隊(duì)列彈出一個(gè)協(xié)程的包裝結(jié)構(gòu)sudog
   if sg := c.recvq.dequeue(); sg != nil {
      // 如果能彈出，即有等到接收的協(xié)程，說(shuō)明：
      // 該channel要么是無(wú)緩沖，要么緩沖區(qū)為空，不然不可能有協(xié)程在等待
      // 將要發(fā)送的數(shù)據(jù)拷貝到該協(xié)程的接收指針上
      send(c, sg, ep, func() { unlock(&c.lock) }, 3)
      return  true
}

   // 緩沖區(qū)還有空間
   if c.qcount < c.dataqsiz {
      // qp：計(jì)算要發(fā)送到的位置的地址
      qp := chanbuf(c, c.sendx)
      // 將數(shù)據(jù)從ep拷貝到qp
      typedmemmove(c.elemtype, qp, ep)
      // 待發(fā)送位置移動(dòng)
      c.sendx++
      // 由于是數(shù)組模擬隊(duì)列，sendx到頂了需要?dú)w零
      if c.sendx == c.dataqsiz {
         c.sendx = 0
      }
      // 緩沖區(qū)數(shù)量++
      c.qcount++
      unlock(&c.lock)
      return  true
}

   // 往下就是緩沖區(qū)無(wú)數(shù)據(jù)，也沒(méi)有等到接收協(xié)程的情況了
   
   // 如果是非阻塞模式，直接返回
   if !block {
      unlock(&c.lock)
      return  false
    }

   // 將當(dāng)前協(xié)程包裝成sudog，阻塞到channel上
   gp := getg()
   mysg := acquireSudog()
   mysg.releasetime = 0
   if t0 != 0 {
      mysg.releasetime = -1
   }
  
   mysg.elem = ep
   mysg.waitlink = nil
   mysg.g = gp
   mysg.isSelect = false
   mysg.c = c
   gp.waiting = mysg
   gp.param = nil
   
   // 當(dāng)前協(xié)程進(jìn)入發(fā)送等待隊(duì)列
   c.sendq.enqueue(mysg)
   atomic.Store8(&gp.parkingOnChan, 1)
   gopark(chanparkcommit, unsafe.Pointer(&c.lock), waitReasonChanSend, traceEvGoBlockSend, 2)
   
 // 被喚醒后從這里開(kāi)始執(zhí)行
   
   KeepAlive(ep)

   if mysg != gp.waiting {
      throw( "G waiting list is corrupted" )
   }
   gp.waiting = nil
   gp.activeStackChans = false
   closed := !mysg.success
   gp.param = nil
   if mysg.releasetime > 0 {
      blockevent(mysg.releasetime-t0, 2)
   }
   mysg.c = nil
   releaseSudog(mysg)
   // 被喚醒后發(fā)現(xiàn)channel關(guān)閉了，panic
   if closed {
      if c.closed == 0 {
         throw( "chansend: spurious wakeup" )
      }
      panic(plainError( "send on closed channel" ))
   }
   return  true
}

type sudog struct {
   // 協(xié)程
   g *g
   // 前一個(gè)，后一個(gè)指針
   next *sudog
   prev *sudog
   // 等到發(fā)送的數(shù)據(jù)在哪，等待從哪個(gè)位置接收數(shù)據(jù)
   elem unsafe.Pointer
   acquiretime int64
   releasetime int64
   ticket      uint32
   isSelect bool
   success bool

   parent   *sudog // semaRoot binary tree
   waitlink *sudog // g.waiting list or semaRoot
   waittail *sudog // semaRoot
   // 在哪個(gè)channel上等待
   c        *hchan // channel
}

func full(c *hchan) bool {
   // 無(wú)緩沖
   if c.dataqsiz == 0 {
      // 并且沒(méi)有其他協(xié)程在等待
      return c.recvq.first == nil
   }
   // 有緩沖，但容量裝滿了
   return c.qcount == c.dataqsiz
}

/**
c：要操作的channel
sg：彈出的接收者協(xié)程
ep：要發(fā)送的數(shù)據(jù)在的位置
*/
func send(c *hchan, sg *sudog, ep unsafe.Pointer, unlockf func(), skip int) {
   // 如果接收者指針不為空，直接把數(shù)據(jù)從ep拷貝到sg.elem
   if sg.elem != nil {
      sendDirect(c.elemtype, sg, ep)
      sg.elem = nil
   }
   gp := sg.g
   unlockf()
   gp.param = unsafe.Pointer(sg)
   sg.success = true
   if sg.releasetime != 0 {
      sg.releasetime = cputicks()
   }
   // 喚醒該接收者協(xié)程
   goready(gp, skip+1)
}

func chanrecv1(c *hchan, elem unsafe.Pointer) {
        chanrecv(c, elem, true)
}

func chanrecv2(c *hchan, elem unsafe.Pointer) (received bool) {
        _, received = chanrecv(c, elem, true)
        return
}

func chanrecv(c *hchan, ep unsafe.Pointer, block bool) (selected, received bool) {
    // 如果channel為nil，根據(jù)參數(shù)中是否阻塞來(lái)決定是否阻塞
   if c == nil {
      if !block {
         return
   }
      gopark(nil, nil, waitReasonChanReceiveNilChan, traceEvGoStop, 2)
      throw( "unreachable" )
   }

   // 非阻塞，并且channel為空
   if !block && empty(c) {
      // 如果還沒(méi)關(guān)閉，直接返回
   if atomic.Load(&c.closed) == 0 {
      return
   }
      // 否則已經(jīng)關(guān)閉，
      // 如果為空，返回該類(lèi)型的零值
   if empty(c) {
     if ep != nil {
        typedmemclr(c.elemtype, ep)
     }
     return  true, false
       }
   }

   lock(&c.lock)
   
   // 同樣，如果channel已經(jīng)關(guān)閉，且緩沖區(qū)沒(méi)有元素，返回該類(lèi)型零值
   if c.closed != 0 && c.qcount == 0 {
      unlock(&c.lock)
      if ep != nil {
         typedmemclr(c.elemtype, ep)
      }
      return  true, false
}
    
   // 如果有發(fā)送者正在阻塞，說(shuō)明：
   // 1.無(wú)緩沖
   // 2.有緩沖，但緩沖區(qū)滿了。因?yàn)橹挥芯彌_區(qū)滿了，才可能有發(fā)送者在等待
   if sg := c.sendq.dequeue(); sg != nil {
      // 將數(shù)據(jù)從緩沖區(qū)拷貝到ep，再將sg的數(shù)據(jù)拷貝到緩沖區(qū)，該函數(shù)詳細(xì)流程可看下文
      recv(c, sg, ep, func() { unlock(&c.lock) }, 3)
      return  true, true
}
    
   // 如果緩存區(qū)有數(shù)據(jù)， 
   if c.qcount > 0 {
      // qp為緩沖區(qū)中下一次接收的位置
      qp := chanbuf(c, c.recvx)
      // 將數(shù)據(jù)從qp拷貝到ep
      if ep != nil {
         typedmemmove(c.elemtype, ep, qp)
      }
      typedmemclr(c.elemtype, qp)
      c.recvx++
      if c.recvx == c.dataqsiz {
         c.recvx = 0
      }
      c.qcount--
      unlock(&c.lock)
      return  true, true
}

   // 接下來(lái)就是既沒(méi)有發(fā)送者在等待，也緩沖區(qū)也沒(méi)數(shù)據(jù)
   if !block {
      unlock(&c.lock)
      return  false, false
}

   // 將當(dāng)前協(xié)程包裝成sudog，阻塞到channel中
   gp := getg()
   mysg := acquireSudog()
   mysg.releasetime = 0
   if t0 != 0 {
      mysg.releasetime = -1
   }
   // 記錄接收地址
   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)

   atomic.Store8(&gp.parkingOnChan, 1)
   gopark(chanparkcommit, unsafe.Pointer(&c.lock), waitReasonChanReceive,        traceEvGoBlockRecv, 2)

   // 從這里喚醒
   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
}

/**
c：操作的channel
sg：阻塞的發(fā)送協(xié)程
ep：接收者接收數(shù)據(jù)的地址
*/
func recv(c *hchan, sg *sudog, ep unsafe.Pointer, unlockf func(), skip int) {
   // 如果是無(wú)緩沖channel，直接將數(shù)據(jù)從發(fā)送者sg拷貝到ep
   if c.dataqsiz == 0 {
      if ep != nil {
         recvDirect(c.elemtype, sg, ep)
      }
   // 接下來(lái)是有緩沖，且緩沖區(qū)滿的情況   
   } else {
      // qp為channel緩沖區(qū)中，接收者下一次接收的地址
   qp := chanbuf(c, c.recvx)
      // 將數(shù)據(jù)從qp拷貝到ep
   if ep != nil {
         typedmemmove(c.elemtype, ep, qp)
    }
    // 將發(fā)送者的數(shù)據(jù)從sg.elem拷貝到qp
    typedmemmove(c.elemtype, qp, sg.elem)
    c.recvx++
    if c.recvx == c.dataqsiz {
       c.recvx = 0
    }
    // 由于一接收已發(fā)送，緩沖區(qū)還是滿的，因此 c.sendx = c.recvx
    c.sendx = c.recvx 
}
   sg.elem = nil
   gp := sg.g
   unlockf()
   gp.param = unsafe.Pointer(sg)
   sg.success = true
   if sg.releasetime != 0 {
      sg.releasetime = cputicks()
   }
   // 喚醒發(fā)送者
   goready(gp, skip+1)
}

func closechan(c *hchan) {
   // 不能關(guān)閉空channel
   if c == nil {
      panic(plainError( "close of nil channel" ))
   }

   lock(&c.lock)
   // 不能重復(fù)關(guān)閉
   if c.closed != 0 {
      unlock(&c.lock)
      panic(plainError( "close of closed channel" ))
   }

   // 修改關(guān)閉狀態(tài)
   c.closed = 1

   var glist gList

   // 釋放所有的接收者協(xié)程，并為它們賦予零值
 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
      glist.push(gp)
   }

   // 釋放所有的發(fā)送者協(xié)程
 for {
      sg := c.sendq.dequeue()
      if sg == nil {
         break
     }
      sg.elem = nil
      if sg.releasetime != 0 {
         sg.releasetime = cputicks()
      }
      gp := sg.g
      gp.param = unsafe.Pointer(sg)
      sg.success = false
      glist.push(gp)
   }
   unlock(&c.lock)

   // 執(zhí)行喚醒操作
 for !glist.empty() {
      gp := glist.pop()
      gp.schedlink = 0
      goready(gp, 3)
   }
}