源码 锁 自旋 Spin go程调度顺序 死锁 读写锁 go程 均分时间片
github.com\google\gopacket@v1.1.19\pcap\pcap_windows.go
switch goroutines
// waitForPacket waits for a packet or for the timeout to expire.
func (p *Handle) waitForPacket() {
// can't use select() so instead just switch goroutines
runtime.Gosched()
}
func labLock() {
log.Println("in-0")
var Num int
var NumMax int = 4
var concurrenceRWLockNum sync.RWMutex
concurrenceRWLockNum.RLock()
if Num == NumMax {
concurrenceRWLockNum.RUnlock()
return
} else {
concurrenceRWLockNum.Lock()
if Num < NumMax {
Num++
defer func() {
concurrenceRWLockNum.Lock()
Num--
concurrenceRWLockNum.Unlock()
}()
}
concurrenceRWLockNum.Unlock()
concurrenceRWLockNum.RUnlock()
}
log.Println("in-1")
}
fatal error: all goroutines are asleep - deadlock!
goroutine 1 [semacquire]:
sync.runtime_SemacquireMutex(0x56c807?, 0x18?, 0x61dda0?)
C:/Program Files/Go/src/runtime/sema.go:77 +0x25
sync.(*RWMutex).Lock(0x0?)
C:/Program Files/Go/src/sync/rwmutex.go:152 +0x71
main.labLock()
/main.go:29 +0x98
} else {
main.main()
修正，调整顺序
concurrenceRWLockNum.RUnlock()
concurrenceRWLockNum.Lock()
Go\src\sync\runtime.go
// runtime_doSpin does active spinning.
func runtime_doSpin()
Go\src\sync\mutex.go
// Lock locks m.
// If the lock is already in use, the calling goroutine
// blocks until the mutex is available.
func (m *Mutex) Lock() {
// Fast path: grab unlocked mutex.
if atomic.CompareAndSwapInt32(&m.state, 0, mutexLocked) {
if race.Enabled {
race.Acquire(unsafe.Pointer(m))
}
return
}
// Slow path (outlined so that the fast path can be inlined)
m.lockSlow()
}
// TryLock tries to lock m and reports whether it succeeded.
//
// Note that while correct uses of TryLock do exist, they are rare,
// and use of TryLock is often a sign of a deeper problem
// in a particular use of mutexes.
func (m *Mutex) TryLock() bool {
old := m.state
if old&(mutexLocked|mutexStarving) != 0 {
return false
}
// There may be a goroutine waiting for the mutex, but we are
// running now and can try to grab the mutex before that
// goroutine wakes up.
if !atomic.CompareAndSwapInt32(&m.state, old, old|mutexLocked) {
return false
}
if race.Enabled {
race.Acquire(unsafe.Pointer(m))
}
return true
}
func (m *Mutex) lockSlow() {
var waitStartTime int64
starving := false
awoke := false
iter := 0
old := m.state
for {
// Don't spin in starvation mode, ownership is handed off to waiters
// so we won't be able to acquire the mutex anyway.
if old&(mutexLocked|mutexStarving) == mutexLocked && 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++
old = m.state
continue
}
new := old
// Don't try to acquire starving mutex, new arriving goroutines must queue.
if old&mutexStarving == 0 {
new |= mutexLocked
}
if old&(mutexLocked|mutexStarving) != 0 {
new += 1 << mutexWaiterShift
}
// The current goroutine switches mutex to starvation mode.
// But if the mutex is currently unlocked, don't do the switch.
// Unlock expects that starving mutex has waiters, which will not
// be true in this case.
if starving && old&mutexLocked != 0 {
new |= mutexStarving
}
if awoke {
// The goroutine has been woken from sleep,
// so we need to reset the flag in either case.
if new&mutexWoken == 0 {
throw("sync: inconsistent mutex state")
}
new &^= mutexWoken
}
if atomic.CompareAndSwapInt32(&m.state, old, new) {
if old&(mutexLocked|mutexStarving) == 0 {
break // locked the mutex with CAS
}
// If we were already waiting before, queue at the front of the queue.
queueLifo := waitStartTime != 0
if waitStartTime == 0 {
waitStartTime = runtime_nanotime()
}
runtime_SemacquireMutex(&m.sema, queueLifo, 1)
starving = starving || runtime_nanotime()-waitStartTime > starvationThresholdNs
old = m.state
if old&mutexStarving != 0 {
// If this goroutine was woken and mutex is in starvation mode,
// ownership was handed off to us but mutex is in somewhat
// inconsistent state: mutexLocked is not set and we are still
// accounted as waiter. Fix that.
if old&(mutexLocked|mutexWoken) != 0 || old>>mutexWaiterShift == 0 {
throw("sync: inconsistent mutex state")
}
delta := int32(mutexLocked - 1<<mutexWaiterShift)
if !starving || old>>mutexWaiterShift == 1 {
// Exit starvation mode.
// Critical to do it here and consider wait time.
// Starvation mode is so inefficient, that two goroutines
// can go lock-step infinitely once they switch mutex
// to starvation mode.
delta -= mutexStarving
}
atomic.AddInt32(&m.state, delta)
break
}
awoke = true
iter = 0
} else {
old = m.state
}
}
if race.Enabled {
race.Acquire(unsafe.Pointer(m))
}
}
func labLock() {
log.Println("in-0")
var wg sync.WaitGroup
N := 16
wg.Add(N + N)
var lk sync.RWMutex
for i := 0; i < N; i++ {
go func(i int) {
defer wg.Done()
lk.Lock()
log.Println("1=", i)
time.Sleep(2 * time.Second)
lk.Unlock()
}(i)
}
for i := 0; i < N; i++ {
go func(i int) {
defer wg.Done()
lk.Lock()
log.Println("2=", i)
time.Sleep(2 * time.Second)
lk.Unlock()
}(i)
}
wg.Wait()
log.Println("in-1")
}
2022/09/02 09:23:29 in-0 2022/09/02 09:23:29 1= 8 2022/09/02 09:23:31 2= 2 2022/09/02 09:23:33 1= 9 2022/09/02 09:23:35 1= 10 2022/09/02 09:23:37 1= 11 2022/09/02 09:23:39 1= 12 2022/09/02 09:23:41 1= 13 2022/09/02 09:23:43 1= 14 2022/09/02 09:23:45 1= 15 2022/09/02 09:23:47 2= 0 2022/09/02 09:23:49 2= 1 2022/09/02 09:23:51 2= 15 2022/09/02 09:23:53 2= 6 2022/09/02 09:23:55 2= 7 2022/09/02 09:23:57 2= 8 2022/09/02 09:23:59 2= 9 2022/09/02 09:24:01 2= 10 2022/09/02 09:24:03 2= 11 2022/09/02 09:24:05 2= 12 2022/09/02 09:24:07 2= 13 2022/09/02 09:24:09 2= 14 2022/09/02 09:24:11 1= 5 2022/09/02 09:24:13 2= 5 2022/09/02 09:24:15 2= 3 2022/09/02 09:24:17 1= 4 2022/09/02 09:24:19 2= 4 2022/09/02 09:24:21 1= 6 2022/09/02 09:24:23 1= 1 2022/09/02 09:24:25 1= 7 2022/09/02 09:24:27 1= 0 2022/09/02 09:24:29 1= 2 2022/09/02 09:24:31 1= 3 2022/09/02 09:24:33 in-1
