type hchan struct {

   qcount   uint           // 當前隊列中剩余元素個數(shù)

   dataqsiz uint           // 環(huán)形隊列長度，即可以存放的元素個數(shù)

   buf      unsafe.Pointer // 環(huán)形隊列指針

   elemsize uint16         // 每個元素的大小

   closed   uint32         // 標記是否關閉

   elemtype *_type         // 元素類型

   sendx    uint           // 隊列下標，指向元素寫入時存放到隊列中的位置

   recvx    uint           // 隊列下標，指向元素從隊列中讀出的位置

   recvq    waitq          // 等待讀消息的groutine隊列

   sendq    waitq          // 等待寫消息的groutine隊列

   lock     mutex          // 互斥鎖

}

type waitq struct {
   first *sudog
   last  *sudog
}

type sudog struct {
   g            *g
   next         *sudog
   prev         *sudog
   elem         unsafe.Pointer // data element (may point to stack)
   
   acquiretime  int64
   releasetime  int64
   ticket       uint32
   isSelect     bool
   
   parent       *sudog // semaRoot binary tree
   waitlink     *sudog // g.waiting list or semaRoot
   waittail     *sudog // semaRoot
   c            *hchan // channel
}

func makechan(t *chantype, size int) *hchan {
   elem := t.elem

   // compiler checks this but be safe.
   if elem.size >= 1<<16 {
      throw("makechan: invalid channel element type")
   }
   if hchanSize%maxAlign != 0 || elem.align > maxAlign {
      throw("makechan: bad alignment")
   }

   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 {
   
   case mem == 0:
   // 如果當前 Channel 中不存在緩沖區(qū)，那么就只會為 runtime.hchan 分配一段內存空間；
      c = (*hchan)(mallocgc(hchanSize, nil, true))
      c.buf = c.raceaddr()
   case elem.ptrdata == 0:
   // 如果當前 Channel 中存儲的類型不是指針類型，會為當前的 Channel 和底層的數(shù)組分配一塊連續(xù)的內存空間；
      c = (*hchan)(mallocgc(hchanSize+mem, nil, true))
      c.buf = add(unsafe.Pointer(c), hchanSize)
   default:
   //單獨為 runtime.hchan 和緩沖區(qū)分配內存；
      c = new(hchan)
      c.buf = mallocgc(mem, elem, true)
   }

   c.elemsize = uint16(elem.size)
   c.elemtype = elem
   c.dataqsiz = uint(size)
   lockInit(&c.lock, lockRankHchan)
   // 在函數(shù)的最后會統(tǒng)一更新elemsize、elemtype 和 dataqsiz 幾個字段;
   if debugChan {
      print("makechan: chan=", c, "; elemsize=", elem.size, "; dataqsiz=", size, "\n")
   }
   return c
}

func chansend(c *hchan, ep unsafe.Pointer, block bool, callerpc uintptr) bool {
   .....
   lock(&c.lock)

   if c.closed != 0 {
      unlock(&c.lock)
      panic(plainError("send on closed channel"))
   }

   // 如果Channel 沒有被關閉并且已經有處于讀等待的 Goroutine，
   // 那么從接收隊列 recvq 中取出最先陷入等待的 Goroutine 并直接向它發(fā)送數(shù)據
   if sg := c.recvq.dequeue(); sg != nil {
      send(c, sg, ep, func() { unlock(&c.lock) }, 3)
      return true
   }
   
   // 如果recvq為空且緩沖區(qū)中還有剩余空間
   if c.qcount < c.dataqsiz {
   // 計算出下一個可以存儲數(shù)據的位置，
      qp := chanbuf(c, c.sendx)
      // raceenabled: 是否啟用數(shù)據競爭檢測，在編譯時指定，默認為false
      if raceenabled {
      // 發(fā)出數(shù)據競爭警告
         raceacquire(qp)
         racerelease(qp)
      }
      // 將發(fā)送的數(shù)據拷貝到緩沖區(qū)中，產生內存拷貝
      typedmemmove(c.elemtype, qp, ep)
      // 增加 sendx 索引
      c.sendx++
      if c.sendx == c.dataqsiz {
         c.sendx = 0
      }
      // 增加計數(shù)器
      c.qcount++
      unlock(&c.lock)
      return true
   }
   
   if !block {
      unlock(&c.lock)
      return false
   }

   // 將channel數(shù)據綁定到當前groutine并使groutine休眠
   // 獲取發(fā)送數(shù)據使用的 Goroutine
   gp := getg()
   // 獲取 runtime.sudog 結構并設置這一次阻塞發(fā)送的相關信息，
   // 例如發(fā)送的 Channel、是否在 select 中和待發(fā)送數(shù)據的內存地址等
   mysg := acquireSudog()
   mysg.releasetime = 0
   if t0 != 0 {
      mysg.releasetime = -1
   }
   // 將剛剛創(chuàng)建并初始化的 mysg 加入發(fā)送等待隊列，并設置到當前 Goroutine的waiting上，
   // 表示 Goroutine 正在等待該sudog準備就緒
   mysg.elem = ep
   mysg.waitlink = nil
   mysg.g = gp
   mysg.isSelect = false
   mysg.c = c
   gp.waiting = mysg
   gp.param = nil
   c.sendq.enqueue(mysg)
   // 休眠groutine
   gopark(chanparkcommit, unsafe.Pointer(&c.lock), waitReasonChanSend, traceEvGoBlockSend, 2)
   // 保證傳入的數(shù)據不被GC
   KeepAlive(ep)

   // someone woke us up.
   if mysg != gp.waiting {
      throw("G waiting list is corrupted")
   }
   gp.waiting = nil
   gp.activeStackChans = false
   if gp.param == nil {
      if c.closed == 0 {
         throw("chansend: spurious wakeup")
      }
      panic(plainError("send on closed channel"))
   }
   gp.param = nil
   if mysg.releasetime > 0 {
      blockevent(mysg.releasetime-t0, 2)
   }
   mysg.c = nil
   releaseSudog(mysg)
   return true
}

func chanrecv(c *hchan, ep unsafe.Pointer, block bool) (selected, received bool) {
 // block：這次接收是否阻塞
   if debugChan {
      print("chanrecv: chan=", c, "\n")
   }

   if c == nil {
      if !block {
         return
      }
      // 從一個空 Channel 接收數(shù)據時會直接讓出處理器的使用權
      gopark(nil, nil, waitReasonChanReceiveNilChan, traceEvGoStop, 2)
      throw("unreachable")
   }

   // Fast path: check for failed non-blocking operation without acquiring the lock.
   if !block && empty(c) {
     // 如果channel為空并且未關閉，直接返回
      if atomic.Load(&c.closed) == 0 {
         return
      }

      if empty(c) {
         // The channel is irreversibly closed and empty.
         if raceenabled {
            raceacquire(c.raceaddr())
         }
         if ep != nil {
         // 手動標記清楚對象
            typedmemclr(c.elemtype, ep)
         }
         return true, false
      }
   }

   var t0 int64
   if blockprofilerate > 0 {
      t0 = cputicks()
   }

   lock(&c.lock)
    //如果channel為空，并且已關閉，說明對象不可達
   if c.closed != 0 && c.qcount == 0 {
      if raceenabled {
         raceacquire(c.raceaddr())
      }
      unlock(&c.lock)
      if ep != nil {
      // 手動標記清除
         typedmemclr(c.elemtype, ep)
      }
      return true, false
   }
    // 如果sendq不為空，直接消費，避免sendq --> queue --> recvx的過程
   if sg := c.sendq.dequeue(); sg != nil {
      recv(c, sg, ep, func() { unlock(&c.lock) }, 3)
      return true, true
   }
    
    // 當 Channel 的緩沖區(qū)中已經包含數(shù)據時，從 Channel 中接收數(shù)據會直接從緩沖區(qū)中 
    // recvx 的索引位置中取出數(shù)據進行處理
   if c.qcount > 0 {
      // Receive directly from queue
      qp := chanbuf(c, c.recvx)
      if raceenabled {
         raceacquire(qp)
         racerelease(qp)
      }
      // 如果接收數(shù)據的內存地址不為空，那么會使用 runtime.typedmemmove將緩沖區(qū)中的數(shù)據拷貝到內存中
      if ep != nil {
         typedmemmove(c.elemtype, ep, qp)
      }
      // 使用 runtime.typedmemclr清除隊列中的數(shù)據并完成收尾工作
      typedmemclr(c.elemtype, qp)
      c.recvx++
      // recvx位置歸零
      if c.recvx == c.dataqsiz {
         c.recvx = 0
      }
      c.qcount-- // 計數(shù)減一
      unlock(&c.lock) 
      return true, true
   }

   if !block {
      unlock(&c.lock)
      return false, false
   }

   // 當 sendq不為空 并且緩沖區(qū)中也不存在任何數(shù)據時，阻塞并休眠當前groutine
   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)
   gopark(chanparkcommit, unsafe.Pointer(&c.lock), waitReasonChanReceive, traceEvGoBlockRecv, 2)

   // someone woke us up
   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)
   }
   closed := gp.param == nil
   gp.param = nil
   mysg.c = nil
   releaseSudog(mysg)
   return true, !closed
}