/
mutex.go
64 lines (54 loc) · 1.74 KB
/
mutex.go
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package mutex
import (
"sync"
"sync/atomic"
"unsafe"
)
// 复制Mutex定义的常量
const (
mutexLocked = 1 << iota // 加锁标识位置
mutexWoken // 唤醒标识位置
mutexStarving // 锁饥饿标识位置
mutexWaiterShift = iota // 标识waiter的起始bit位置
)
// Mutex 支持 TryLock
type Mutex struct {
sync.Mutex
}
func (m *Mutex) TryLock() bool {
// 如果能成功抢到锁
if atomic.CompareAndSwapInt32((*int32)(unsafe.Pointer(&m.Mutex)), 0, mutexLocked) {
return true
}
// 如果处于唤醒、加锁或者饥饿状态,这次请求就不参与竞争了,返回false
old := atomic.LoadInt32((*int32)(unsafe.Pointer(&m.Mutex)))
if old&(mutexLocked|mutexStarving|mutexWoken) != 0 {
return false
}
// 尝试在竞争的状态下请求锁
_new := old | mutexLocked
return atomic.CompareAndSwapInt32((*int32)(unsafe.Pointer(&m.Mutex)), old, _new)
}
// Count 指标信息 获取等待锁的数量
func (m *Mutex) Count() int {
// 获取state字段的值
v := atomic.LoadInt32((*int32)(unsafe.Pointer(&m.Mutex)))
v = v >> mutexWaiterShift // 得到等待者的数值
v = v + (v & mutexLocked) // 再加上锁持有者的数量,0或者1
return int(v)
}
// IsLocked 锁是否被持有
func (m *Mutex) IsLocked() bool {
state := atomic.LoadInt32((*int32)(unsafe.Pointer(&m.Mutex)))
return state&mutexLocked == mutexLocked
}
// IsWoken 是否有等待者被唤醒
func (m *Mutex) IsWoken() bool {
state := atomic.LoadInt32((*int32)(unsafe.Pointer(&m.Mutex)))
return state&mutexWoken == mutexWoken
}
// IsStarving 锁是否处于饥饿状态
func (m *Mutex) IsStarving() bool {
state := atomic.LoadInt32((*int32)(unsafe.Pointer(&m.Mutex)))
return state&mutexStarving == mutexStarving
}