Golang race.Acquire函数代码示例

// Lock 用于锁定 m。
// 若该锁正在使用，调用的Go程就会阻塞，直到该互斥体可用。
func (m *Mutex) Lock() {
	// Fast path: grab unlocked mutex.
	// 快速通道：抢占锁定的互斥体。
	if atomic.CompareAndSwapInt32(&m.state, 0, mutexLocked) {
		if race.Enabled {
			race.Acquire(unsafe.Pointer(m))
		}
		return
	}

	awoke := false
	iter := 0
	for {
		old := m.state
		new := old | mutexLocked
		if old&mutexLocked != 0 {
			if runtime_canSpin(iter) {
				// Active spinning makes sense.
				// Try to set mutexWoken flag to inform Unlock
				// to not wake other blocked goroutines.
				if !awoke && old&mutexWoken == 0 && old>>mutexWaiterShift != 0 &&
					atomic.CompareAndSwapInt32(&m.state, old, old|mutexWoken) {
					awoke = true
				}
				runtime_doSpin()
				iter++
				continue
			}
			new = old + 1<<mutexWaiterShift
		}
		if awoke {
			// The goroutine has been woken from sleep,
			// so we need to reset the flag in either case.
			// 此Go程已从睡眠状态被唤醒，因此无论在哪种状态下，
			// 我们都需要充值此标记。
			if new&mutexWoken == 0 {
				panic("sync: inconsistent mutex state")
			}
			new &^= mutexWoken
		}
		if atomic.CompareAndSwapInt32(&m.state, old, new) {
			if old&mutexLocked == 0 {
				break
			}
			runtime_Semacquire(&m.sema)
			awoke = true
			iter = 0
		}
	}

	if race.Enabled {
		race.Acquire(unsafe.Pointer(m))
	}
}

// Get selects an arbitrary item from the Pool, removes it from the
// Pool, and returns it to the caller.
// Get may choose to ignore the pool and treat it as empty.
// Callers should not assume any relation between values passed to Put and
// the values returned by Get.
//
// If Get would otherwise return nil and p.New is non-nil, Get returns
// the result of calling p.New.
func (p *Pool) Get() interface{} {
	if race.Enabled {
		race.Disable()
	}
	l := p.pin()
	x := l.private
	l.private = nil
	runtime_procUnpin()
	if x == nil {
		l.Lock()
		last := len(l.shared) - 1
		if last >= 0 {
			x = l.shared[last]
			l.shared = l.shared[:last]
		}
		l.Unlock()
		if x == nil {
			x = p.getSlow()
		}
	}
	if race.Enabled {
		race.Enable()
		if x != nil {
			race.Acquire(poolRaceAddr(x))
		}
	}
	if x == nil && p.New != nil {
		x = p.New()
	}
	return x
}

// Lock locks rw for writing.
// If the lock is already locked for reading or writing,
// Lock blocks until the lock is available.
// To ensure that the lock eventually becomes available,
// a blocked Lock call excludes new readers from acquiring
// the lock.
func (rw *RWMutex) Lock() {
	if race.Enabled {
		_ = rw.w.state
		race.Disable()
	}
	// First, resolve competition with other writers.
	rw.w.Lock()
	// Announce to readers there is a pending writer.
	r := atomic.AddInt32(&rw.readerCount, -rwmutexMaxReaders) + rwmutexMaxReaders
	// Wait for active readers.
	if r != 0 && atomic.AddInt32(&rw.readerWait, r) != 0 {
		runtime_Semacquire(&rw.writerSem)
	}
	if race.Enabled {
		race.Enable()
		race.Acquire(unsafe.Pointer(&rw.readerSem))
		race.Acquire(unsafe.Pointer(&rw.writerSem))
	}
}

// Wait 阻塞 WaitGroup 直到其 counter 为零。
func (wg *WaitGroup) Wait() {
	statep := wg.state()
	if race.Enabled {
		_ = *statep // trigger nil deref early
		race.Disable()
	}
	for {
		state := atomic.LoadUint64(statep)
		v := int32(state >> 32)
		w := uint32(state)
		if v == 0 {
			// Counter is 0, no need to wait.
			// 计数器为 0，无需等待。
			if race.Enabled {
				race.Enable()
				race.Acquire(unsafe.Pointer(wg))
			}
			return
		}
		// Increment waiters count.
		// 递增等待者计数。
		if atomic.CompareAndSwapUint64(statep, state, state+1) {
			if race.Enabled && w == 0 {
				// Wait must be synchronized with the first Add.
				// Need to model this is as a write to race with the read in Add.
				// As a consequence, can do the write only for the first waiter,
				// otherwise concurrent Waits will race with each other.
				race.Write(unsafe.Pointer(&wg.sema))
			}
			runtime_Semacquire(&wg.sema)
			if *statep != 0 {
				panic("sync: WaitGroup is reused before previous Wait has returned")
			}
			if race.Enabled {
				race.Enable()
				race.Acquire(unsafe.Pointer(wg))
			}
			return
		}
	}
}

// RLock locks rw for reading.
func (rw *RWMutex) RLock() {
	if race.Enabled {
		_ = rw.w.state
		race.Disable()
	}
	if atomic.AddInt32(&rw.readerCount, 1) < 0 {
		// A writer is pending, wait for it.
		runtime_Semacquire(&rw.readerSem)
	}
	if race.Enabled {
		race.Enable()
		race.Acquire(unsafe.Pointer(&rw.readerSem))
	}
}

func Read(fd int, p []byte) (n int, err error) {
	n, err = read(fd, p)
	if race.Enabled {
		if n > 0 {
			race.WriteRange(unsafe.Pointer(&p[0]), n)
		}
		if err == nil {
			race.Acquire(unsafe.Pointer(&ioSync))
		}
	}
	if msanenabled && n > 0 {
		msanWrite(unsafe.Pointer(&p[0]), n)
	}
	return
}

func (fd *netFD) Read(buf []byte) (int, error) {
	if err := fd.readLock(); err != nil {
		return 0, err
	}
	defer fd.readUnlock()
	o := &fd.rop
	o.InitBuf(buf)
	n, err := rsrv.ExecIO(o, "WSARecv", func(o *operation) error {
		return syscall.WSARecv(o.fd.sysfd, &o.buf, 1, &o.qty, &o.flags, &o.o, nil)
	})
	if race.Enabled {
		race.Acquire(unsafe.Pointer(&ioSync))
	}
	err = fd.eofError(n, err)
	if _, ok := err.(syscall.Errno); ok {
		err = os.NewSyscallError("wsarecv", err)
	}
	return n, err
}

func Read(fd Handle, p []byte) (n int, err error) {
	var done uint32
	e := ReadFile(fd, p, &done, nil)
	if e != nil {
		if e == ERROR_BROKEN_PIPE {
			// NOTE(brainman): work around ERROR_BROKEN_PIPE is returned on reading EOF from stdin
			return 0, nil
		}
		return 0, e
	}
	if race.Enabled {
		if done > 0 {
			race.WriteRange(unsafe.Pointer(&p[0]), int(done))
		}
		race.Acquire(unsafe.Pointer(&ioSync))
	}
	if msanenabled && done > 0 {
		msanWrite(unsafe.Pointer(&p[0]), int(done))
	}
	return int(done), nil
}