Channel（一）chan数据结构

chan数据结构

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 环形队列指针 
    elemsize uint16 //队列元素大小 
    closed uint32 //标识关闭状态 
    elemtype *_type // element type 元素类型 
    sendx uint // send index 元素可出队下标
     recvx uint // receive index 元素可入队下标 
    recvq waitq // list of recv waiters 接收消息goroutine队列，链表 
    sendq waitq // list of send waiters 发送消息goroutine队列，链表 
    // lock protects all fields in hchan, as well as several 
    // fields in sudogs blocked on this channel. 
    // // Do not change another G's status while holding this lock 
    // (in particular, do not ready a G), as this can deadlock 
    // with stack shrinking.
     //互斥锁， 
    lock mutex 
}

环形队列

创建有缓冲区channel时，如下：

channel := make(chan int, 6) //6: 指定了channel的环形队列大小

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等待队列

channel读写操作：

• 读：无缓冲区或缓冲区空，读goroutine阻塞，被挂起在channel的recvq队列中，直到被写goroutine唤醒
• 写：无缓冲区或缓冲区满，写goroutine阻塞，被挂起在channel的waitq队列中，直到被读goroutine唤醒

无缓冲区的channel结构如下：G阻塞读取数据

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数据结构

//双向链表
type waitq struct {
   first *sudog
   last  *sudog
}

 //被阻塞的goroutine的封装
type sudog struct {
   // The following fields are protected by the hchan.lock of the
   // channel this sudog is blocking on. shrinkstack depends on
   // this for sudogs involved in channel ops.

   g *g

   next *sudog
   prev *sudog
  elem unsafe.Pointer // data element (may point to stack)

   // The following fields are never accessed concurrently.
   // For channels, waitlink is only accessed by g.
   // For semaphores, all fields (including the ones above)
   // are only accessed when holding a semaRoot lock.

   acquiretime int64
   releasetime int64
   ticket      uint32

   // isSelect indicates g is participating in a select, so
   // g.selectDone must be CAS'd to win the wake-up race.
   isSelect bool

   parent   *sudog // semaRoot binary tree
   waitlink *sudog // g.waiting list or semaRoot
   waittail *sudog // semaRoot
   c        *hchan // channel
}

类型信息

一个channel只能用于一种数据类型

• elemsize：标识元素大小，用于定位
• elemtype：标识元素类型

锁

lock实现锁：

• 消费者互斥读
• 生产者互斥写