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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// GOMAXPROCS=10 go test
package sync_test
import (
"runtime"
. "sync"
"testing"
)
func HammerSemaphore(s *uint32, loops int, cdone chan bool) {
for i := 0; i < loops; i++ {
Runtime_Semacquire(s)
Runtime_Semrelease(s)
}
cdone <- true
}
func TestSemaphore(t *testing.T) {
s := new(uint32)
*s = 1
c := make(chan bool)
for i := 0; i < 10; i++ {
go HammerSemaphore(s, 1000, c)
}
for i := 0; i < 10; i++ {
<-c
}
}
func BenchmarkUncontendedSemaphore(b *testing.B) {
s := new(uint32)
*s = 1
HammerSemaphore(s, b.N, make(chan bool, 2))
}
func BenchmarkContendedSemaphore(b *testing.B) {
b.StopTimer()
s := new(uint32)
*s = 1
c := make(chan bool)
defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(2))
b.StartTimer()
go HammerSemaphore(s, b.N/2, c)
go HammerSemaphore(s, b.N/2, c)
<-c
<-c
}
func HammerMutex(m *Mutex, loops int, cdone chan bool) {
for i := 0; i < loops; i++ {
m.Lock()
m.Unlock()
}
cdone <- true
}
func TestMutex(t *testing.T) {
m := new(Mutex)
c := make(chan bool)
for i := 0; i < 10; i++ {
go HammerMutex(m, 1000, c)
}
for i := 0; i < 10; i++ {
<-c
}
}
func TestMutexPanic(t *testing.T) {
defer func() {
if recover() == nil {
t.Fatalf("unlock of unlocked mutex did not panic")
}
}()
var mu Mutex
mu.Lock()
mu.Unlock()
mu.Unlock()
}
func BenchmarkMutexUncontended(b *testing.B) {
type PaddedMutex struct {
Mutex
pad [128]uint8
}
b.RunParallel(func(pb *testing.PB) {
var mu PaddedMutex
for pb.Next() {
mu.Lock()
mu.Unlock()
}
})
}
func benchmarkMutex(b *testing.B, slack, work bool) {
var mu Mutex
if slack {
b.SetParallelism(10)
}
b.RunParallel(func(pb *testing.PB) {
foo := 0
for pb.Next() {
mu.Lock()
mu.Unlock()
if work {
for i := 0; i < 100; i++ {
foo *= 2
foo /= 2
}
}
}
_ = foo
})
}
func BenchmarkMutex(b *testing.B) {
benchmarkMutex(b, false, false)
}
func BenchmarkMutexSlack(b *testing.B) {
benchmarkMutex(b, true, false)
}
func BenchmarkMutexWork(b *testing.B) {
benchmarkMutex(b, false, true)
}
func BenchmarkMutexWorkSlack(b *testing.B) {
benchmarkMutex(b, true, true)
}
func BenchmarkMutexNoSpin(b *testing.B) {
// This benchmark models a situation where spinning in the mutex should be
// non-profitable and allows to confirm that spinning does not do harm.
// To achieve this we create excess of goroutines most of which do local work.
// These goroutines yield during local work, so that switching from
// a blocked goroutine to other goroutines is profitable.
// As a matter of fact, this benchmark still triggers some spinning in the mutex.
var m Mutex
var acc0, acc1 uint64
b.SetParallelism(4)
b.RunParallel(func(pb *testing.PB) {
c := make(chan bool)
var data [4 << 10]uint64
for i := 0; pb.Next(); i++ {
if i%4 == 0 {
m.Lock()
acc0 -= 100
acc1 += 100
m.Unlock()
} else {
for i := 0; i < len(data); i += 4 {
data[i]++
}
// Elaborate way to say runtime.Gosched
// that does not put the goroutine onto global runq.
go func() {
c <- true
}()
<-c
}
}
})
}
func BenchmarkMutexSpin(b *testing.B) {
// This benchmark models a situation where spinning in the mutex should be
// profitable. To achieve this we create a goroutine per-proc.
// These goroutines access considerable amount of local data so that
// unnecessary rescheduling is penalized by cache misses.
var m Mutex
var acc0, acc1 uint64
b.RunParallel(func(pb *testing.PB) {
var data [16 << 10]uint64
for i := 0; pb.Next(); i++ {
m.Lock()
acc0 -= 100
acc1 += 100
m.Unlock()
for i := 0; i < len(data); i += 4 {
data[i]++
}
}
})
}
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