func HammerSemaphore(s *uint32, loops int, cdone chan bool) {
for i := 0; i < loops; i++ {
runtime.Semacquire(s)
runtime.Semrelease(s)
}
cdone <- true
}
// Lock locks m.
// If the lock is already in use, the calling goroutine
// blocks until the mutex is available.
func (m *Mutex) Lock() {
if xadd(&m.key, 1) == 1 {
// changed from 0 to 1; we hold lock
return
}
runtime.Semacquire(&m.sema)
}
// Lock locks m.
// If the lock is already in use, the calling goroutine
// blocks until the mutex is available.
func (m *Mutex) Lock() {
if atomic.AddInt32(&m.key, 1) == 1 {
// changed from 0 to 1; we hold lock
return
}
runtime.Semacquire(&m.sema)
}
// 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) {
return
}
awoke := false
for {
old := m.state
new := old | mutexLocked
if old&mutexLocked != 0 {
new = old + 1<<mutexWaiterShift
}
if awoke {
// The goroutine has been woken from sleep,
// so we need to reset the flag in either case.
new &^= mutexWoken
}
if atomic.CompareAndSwapInt32(&m.state, old, new) {
if old&mutexLocked == 0 {
break
}
runtime.Semacquire(&m.sema)
awoke = true
}
}
}
func BenchmarkSemaUncontended(b *testing.B) {
type PaddedSem struct {
sem uint32
pad [32]uint32
}
const CallsPerSched = 1000
procs := runtime.GOMAXPROCS(-1)
N := int32(b.N / CallsPerSched)
c := make(chan bool, procs)
for p := 0; p < procs; p++ {
go func() {
sem := new(PaddedSem)
for atomic.AddInt32(&N, -1) >= 0 {
runtime.Gosched()
for g := 0; g < CallsPerSched; g++ {
runtime.Semrelease(&sem.sem)
runtime.Semacquire(&sem.sem)
}
}
c <- true
}()
}
for p := 0; p < procs; p++ {
<-c
}
}
func benchmarkSema(b *testing.B, block, work bool) {
const CallsPerSched = 1000
const LocalWork = 100
procs := runtime.GOMAXPROCS(-1)
N := int32(b.N / CallsPerSched)
c := make(chan bool, procs)
c2 := make(chan bool, procs/2)
sem := uint32(0)
if block {
for p := 0; p < procs/2; p++ {
go func() {
runtime.Semacquire(&sem)
c2 <- true
}()
}
}
for p := 0; p < procs; p++ {
go func() {
foo := 0
for atomic.AddInt32(&N, -1) >= 0 {
runtime.Gosched()
for g := 0; g < CallsPerSched; g++ {
runtime.Semrelease(&sem)
if work {
for i := 0; i < LocalWork; i++ {
foo *= 2
foo /= 2
}
}
runtime.Semacquire(&sem)
}
}
c <- foo == 42
runtime.Semrelease(&sem)
}()
}
if block {
for p := 0; p < procs/2; p++ {
<-c2
}
}
for p := 0; p < procs; p++ {
<-c
}
}
// 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() {
// 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)
}
}
// Wait atomically unlocks c.L and suspends execution
// of the calling goroutine. After later resuming execution,
// Wait locks c.L before returning.
//
// Because L is not locked when Wait first resumes, the caller
// typically cannot assume that the condition is true when
// Wait returns. Instead, the caller should Wait in a loop:
//
// c.L.Lock()
// for !condition() {
// c.Wait()
// }
// ... make use of condition ...
// c.L.Unlock()
//
func (c *Cond) Wait() {
c.m.Lock()
if c.sema == nil {
c.sema = new(uint32)
}
s := c.sema
c.waiters++
c.m.Unlock()
c.L.Unlock()
runtime.Semacquire(s)
c.L.Lock()
}
// Wait blocks until the WaitGroup counter is zero.
func (wg *WaitGroup) Wait() {
wg.m.Lock()
if wg.counter == 0 {
wg.m.Unlock()
return
}
wg.waiters++
if wg.sema == nil {
wg.sema = new(uint32)
}
s := wg.sema
wg.m.Unlock()
runtime.Semacquire(s)
}
// Wait blocks until the WaitGroup counter is zero.
func (wg *WaitGroup) Wait() {
if atomic.LoadInt32(&wg.counter) == 0 {
return
}
wg.m.Lock()
atomic.AddInt32(&wg.waiters, 1)
// This code is racing with the unlocked path in Add above.
// The code above modifies counter and then reads waiters.
// We must modify waiters and then read counter (the opposite order)
// to avoid missing an Add.
if atomic.LoadInt32(&wg.counter) == 0 {
atomic.AddInt32(&wg.waiters, -1)
wg.m.Unlock()
return
}
if wg.sema == nil {
wg.sema = new(uint32)
}
s := wg.sema
wg.m.Unlock()
runtime.Semacquire(s)
}
func (this *Semaphore) P() { runtime.Semacquire((*uint32)(this)) }
func (p *Parker) Park() {
runtime.Semacquire(&p.sema)
}
// RLock locks rw for reading.
func (rw *RWMutex) RLock() {
if atomic.AddInt32(&rw.readerCount, 1) < 0 {
// A writer is pending, wait for it.
runtime.Semacquire(&rw.readerSem)
}
}