Go语言——channel详解

参考:

深入理解Golang Channel

channel和goroutine是go语言最具特色是结构,有必要仔细研究。

源码路径:go1.10\src\runtime\chan.go

struct

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
}

• qcount:当前chann元素个数,len()
• dataqsiz:chann容量,cap()
• buf:元素缓冲区
• elemsize:元素大小
• closed:close标志位
• elemtype:元素类型
• sendx:下一个发送元素所在缓冲区索引
• recvx:下一个接收元素所在缓冲区索引
• recvq:接收G的等待队列
• sendq:发送G的等待队列

从上面可以看出,waitq非常重要

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

waitq是一个queue,具有头尾指针。

sudog封装了等待chann接收/发送的G。

new

chan不能直接new,只能make,所以观察makechan方法。make的时候,会根据size判断是缓冲chan还是非缓冲chan,这个逻辑需要注意。

func makechan(t *chantype, size int) *hchan {
 elem := t.elem
 // Hchan does not contain pointers interesting for GC when elements stored in buf do not contain pointers.
 // buf points into the same allocation, elemtype is persistent.
 // SudoG's are referenced from their owning thread so they can't be collected.
 // TODO(dvyukov,rlh): Rethink when collector can move allocated objects.
 var c *hchan
 switch {
 case size == 0 || elem.size == 0:
 // Queue or element size is zero.
 c = (*hchan)(mallocgc(hchanSize, nil, true))
 // Race detector uses this location for synchronization.
 c.buf = unsafe.Pointer(c)
 case elem.kind&kindNoPointers != 0:
 // Elements do not contain pointers.
 // Allocate hchan and buf in one call.
 c = (*hchan)(mallocgc(hchanSize+uintptr(size)*elem.size, nil, true))
 c.buf = add(unsafe.Pointer(c), hchanSize)
 default:
 // Elements contain pointers.
 c = new(hchan)
 c.buf = mallocgc(uintptr(size)*elem.size, elem, true)
 }
 c.elemsize = uint16(elem.size)
 c.elemtype = elem
 c.dataqsiz = uint(size)
 
 return c
}

这里看到由于要对buf对象分配,所以没有提供new方法,只能make。除了对default情况比较容易理解,另外两只buf的内存分配都不是很理解=。=,先遗留。

send & revc

send

recv

有疑问加站长微信联系(非本文作者)

• 请尽量让自己的回复能够对别人有帮助
• 支持 Markdown 格式, **粗体**、~~删除线~~、`单行代码`
• 支持 @ 本站用户;支持表情(输入 : 提示),见 Emoji cheat sheet
• 图片支持拖拽、截图粘贴等方式上传