Golang互斥锁内部实现的实例详解

本篇文章主要介绍了详解Golang互斥锁内部实现，小编觉得挺不错的，现在分享给大家，也给大家做个参考。一起跟随小编过来看看吧

type Mutex struct {
 state int32   //互斥锁上锁状态枚举值如下所示
 sema uint32  //信号量，向处于Gwaitting的G发送信号
}

const (
 mutexLocked = 1 << iota // 1 互斥锁是锁定的
 mutexWoken       // 2 唤醒锁
 mutexWaiterShift = iota // 2 统计阻塞在这个互斥锁上的goroutine数目需要移位的数值
) 

//go:linkname sync_runtime_canSpin sync.runtime_canSpin
func sync_runtime_canSpin(i int) bool {
 if i >= active_spin || ncpu <= 1 || gomaxprocs <= int32(sched.npidle+sched.nmspinning)+1 {
 return false
 }
 if p := getg().m.p.ptr(); !runqempty(p) {
 return false
 }
 return true
} 

//go:linkname sync_runtime_doSpin sync.runtime_doSpin
func sync_runtime_doSpin() {
 procyield(active_spin_cnt)
} 

//go:linkname sync_runtime_SemacquireMutex sync.runtime_SemacquireMutex
func sync_runtime_SemacquireMutex(addr *uint32) {
 semacquire(addr, semaBlockProfile|semaMutexProfile)
} 

//go:linkname sync_runtime_Semrelease sync.runtime_Semrelease
func sync_runtime_Semrelease(addr *uint32) {
 semrelease(addr)
}
Mutex的Lock函数定义如下

func (m *Mutex) Lock() {
    //先使用CAS尝试获取锁
 if atomic.CompareAndSwapInt32(&m.state, 0, mutexLocked) {
        //这里是-race不需要管它
 if race.Enabled {
  race.Acquire(unsafe.Pointer(m))
 }
        //成功获取返回
 return
 }

 awoke := false //循环标记
 iter := 0    //循环计数器
 for {
 old := m.state //获取当前锁状态
 new := old | mutexLocked //将当前状态最后一位指定1
 if old&mutexLocked != 0 { //如果所以被占用
  if runtime_canSpin(iter) { //检查是否可以进入自旋锁
  if !awoke && old&mutexWoken == 0 && old>>mutexWaiterShift != 0 &&
   atomic.CompareAndSwapInt32(&m.state, old, old|mutexWoken) { 
                    //awoke标记为true
   awoke = true
  }
                //进入自旋状态
  runtime_doSpin()
  iter++
  continue
  }
            //没有获取到锁，当前G进入Gwaitting状态
  new = old + 1<<mutexWaiterShift
 }
 if awoke {
  if new&mutexWoken == 0 {
  throw("sync: inconsistent mutex state")
  }
            //清除标记
  new &^= mutexWoken
 }
        //更新状态
 if atomic.CompareAndSwapInt32(&m.state, old, new) {
  if old&mutexLocked == 0 {
  break
  }
             
            // 锁请求失败,进入休眠状态,等待信号唤醒后重新开始循环
  runtime_SemacquireMutex(&m.sema)
  awoke = true
  iter = 0
 }
 }

 if race.Enabled {
 race.Acquire(unsafe.Pointer(m))
 }
}
Mutex的Unlock函数定义如下

func (m *Mutex) Unlock() {
 if race.Enabled {
 _ = m.state
 race.Release(unsafe.Pointer(m))
 }

 // 移除标记
 new := atomic.AddInt32(&m.state, -mutexLocked)
 if (new+mutexLocked)&mutexLocked == 0 {
 throw("sync: unlock of unlocked mutex")
 }

 old := new
 for {
 //当休眠队列内的等待计数为0或者自旋状态计数器为0，退出
 if old>>mutexWaiterShift == 0 || old&(mutexLocked|mutexWoken) != 0 {
  return
 }
 // 减少等待次数，添加清除标记
 new = (old - 1<<mutexWaiterShift) | mutexWoken
 if atomic.CompareAndSwapInt32(&m.state, old, new) {
            // 释放锁,发送释放信号
  runtime_Semrelease(&m.sema)
  return
 }
 old = m.state
 }
} 

互斥锁无冲突是最简单的情况了，有冲突时，首先进行自旋，，因为大多数的Mutex保护的代码段都很短，经过短暂的自旋就可以获得；如果自旋等待无果，就只好通过信号量来让当前Goroutine进入Gwaitting状态。

以上就是Golang互斥锁内部实现的实例详解的详细内容，更多请关注Gxl网其它相关文章！

查看更多关于Golang互斥锁内部实现的实例详解的详细内容...