golang sudog指的是什么

admin Golang

2024-03-01 0 999

sudog代表在等待队列中的goroutine，比如channel发送接受。由于goroutine和同步对象的关系是多对多，因此需要sudog映射

type sudog struct {
// 指向的goroutine
g *g
// 指向前后sudog的指针
next *sudog
prev *sudog
// 指向数据
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.
// 获取时间
acquiretime int64
// 释放时间
releasetime int64
// 作为队列元素的标识
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
// success indicates whether communication over channel c
// succeeded. It is true if the goroutine was awoken because a
// value was delivered over channel c, and false if awoken
// because c was closed.
success bool
parent *sudog // semaRoot binary tree
waitlink *sudog // g.waiting list or semaRoot
waittail *sudog // semaRoot
c *hchan // channel
}

acquireSudog()

func acquireSudog() *sudog {
// 增加m的锁，防止垃圾回收在此期间被调用
mp := acquirem()
pp := mp.p.ptr()
// 如果本地缓存为空
if len(pp.sudogcache) == 0 {
lock(&sched.sudoglock)
// 从中心缓存迁移至多一半本地缓存容量的缓存项到本地缓存
for len(pp.sudogcache) < cap(pp.sudogcache)/2 && sched.sudogcache != nil {
s := sched.sudogcache
sched.sudogcache = s.next
s.next = nil
pp.sudogcache = append(pp.sudogcache, s)
}
unlock(&sched.sudoglock)
// 若本地缓存仍为空，则新建缓存项
if len(pp.sudogcache) == 0 {
pp.sudogcache = append(pp.sudogcache, new(sudog))
}
}
// 从本地缓存中取出最后一个缓存项返回
n := len(pp.sudogcache)
s := pp.sudogcache[n-1]
pp.sudogcache[n-1] = nil
pp.sudogcache = pp.sudogcache[:n-1]
if s.elem != nil {
throw(\”acquireSudog: found s.elem != nil in cache\”)
}
// 减少m的锁，允许垃圾回收调用
releasem(mp)
return s
}

releaseSudog()

func releaseSudog(s *sudog) {
// 判断sudog各项数据、状态是否正确
if s.elem != nil {
throw(\”runtime: sudog with non-nil elem\”)
}
if s.isSelect {
throw(\”runtime: sudog with non-false isSelect\”)
}
if s.next != nil {
throw(\”runtime: sudog with non-nil next\”)
}
if s.prev != nil {
throw(\”runtime: sudog with non-nil prev\”)
}
if s.waitlink != nil {
throw(\”runtime: sudog with non-nil waitlink\”)
}
if s.c != nil {
throw(\”runtime: sudog with non-nil c\”)
}
gp := getg()
if gp.param != nil {
throw(\”runtime: releaseSudog with non-nil gp.param\”)
}
mp := acquirem() // avoid rescheduling to another P
pp := mp.p.ptr()
// 如果本地缓存满了，就迁移至多一半容量缓存项到中心缓存
if len(pp.sudogcache) == cap(pp.sudogcache) {
// Transfer half of local cache to the central cache.
var first, last *sudog
for len(pp.sudogcache) > cap(pp.sudogcache)/2 {
n := len(pp.sudogcache)
p := pp.sudogcache[n-1]
pp.sudogcache[n-1] = nil
pp.sudogcache = pp.sudogcache[:n-1]
if first == nil {
first = p
} else {
last.next = p
}
last = p
}
lock(&sched.sudoglock)
// 将迁移出来的本地缓存链表直接挂到中心缓存中
last.next = sched.sudogcache
sched.sudogcache = first
unlock(&sched.sudoglock)
}
// 将释放的sudog添加到本地缓存
pp.sudogcache = append(pp.sudogcache, s)
releasem(mp)
}