关于 RWLock 的扩展，我这边给出一段代码（评论不好贴代码，贴个 share link） https://go.dev/play/p/X4YNwqZR4ta ```go package sync import ( "sync" "sync/atomic" "unsafe" ) type RWMutex struct { rw sync.RWMutex } const ( mutexLocked = 1 << iota mutexWake mutexStarving mutexWaiterShift = iota ) const ( rwmutexMaxReaders = 1 << 30 ) func (e *RWMutex) TryLock() bool { if e.GetReader() < 0 { return false } e.rw.Lock() return true } // readerCount > 0 => Reader Hold without Writer, <0 => Reader Hold and Writer waiting, ==0 => no reader // state.mutexLocked == 1 => Writer Hold (in the meanwhile, readerWaiter==0, all reader(readerCount) are waiting) func (e *RWMutex) IsLocked() bool { return e.IsWriterLocked() || e.IsReaderLocked() } func (e *RWMutex) IsWriterLocked() bool { state := atomic.LoadInt32((*int32)(unsafe.Pointer(&e.rw))) return state&mutexLocked == mutexLocked } func (e *RWMutex) IsReaderLocked() bool { return atomic.LoadInt32(e.readerCountPtr()) != 0 } func (e *RWMutex) HasWriter() bool { return atomic.LoadInt32(e.readerCountPtr()) < 0 } func (e *RWMutex) GetWriter() int32 { state := atomic.LoadInt32((*int32)(unsafe.Pointer(&e.rw))) return int32((state >> mutexWaiterShift) + (state & mutexLocked)) } func (e *RWMutex) HasReader() bool { return atomic.LoadInt32(e.readerCountPtr()) != 0 } func (e *RWMutex) GetReader() int32 { r := atomic.LoadInt32(e.readerCountPtr()) if r < 0 { r += rwmutexMaxReaders } return r } func (e *RWMutex) readerCountPtr() *int32 { return (*int32)(unsafe.Pointer(uintptr(unsafe.Pointer(&e.rw)) + unsafe.Sizeof(sync.Mutex{}) + unsafe.Sizeof(uint32(0))*2)) } func (e *RWMutex) readerWaitPtr() *int32 { return (*int32)(unsafe.Pointer(uintptr(unsafe.Pointer(&e.rw)) + unsafe.Sizeof(sync.Mutex{}) + unsafe.Sizeof(uint32(0))*2 + unsafe.Sizeof((int32(0))))) } ```

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))) fmt.Println("===old===:", old) if old&(mutexLocked|mutexStarving|mutexWoken) != 0 { return false } // 尝试在竞争的状态下请求锁 new := old | mutexLocked fmt.Println("===new===:", new) //请问在什么情况下会执行到这里 return atomic.CompareAndSwapInt32((*int32)(unsafe.Pointer(&m.Mutex)), old, new) } func main() { var mu Mutex go func() { // 启动一个goroutine持有一段时间的锁 mu.Lock() time.Sleep(time.Duration(rand.Intn(2)) * time.Second) mu.Unlock() }() time.Sleep(time.Second) n := int(10) var wg sync.WaitGroup wg.Add(n) for i := 0; i < n; i++ { go func() { ok := mu.TryLock() // 尝试获取到锁 defer wg.Done() if ok { // 获取成功 fmt.Println("got the lock") // do something mu.Unlock() return } }() } // 没有获取到 wg.Wait() } 老师，你好。在main中尝试编写一段逻辑测试TryLock方法，请问在什么情况下会执行fmt.Println("===new===:", new) 请老师答疑解惑，谢谢。