1 files changed, 335 insertions, 0 deletions
diff --git a/src/sync/mutex_test.go b/src/sync/mutex_test.go
new file mode 100644
index 0000000..cca0986
--- /dev/null
+++ b/src/sync/mutex_test.go
@@ -0,0 +1,335 @@
+// 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 (
+	"fmt"
+	"internal/testenv"
+	"os"
+	"os/exec"
+	"runtime"
+	"strings"
+	. "sync"
+	"testing"
+	"time"
+)
+
+func HammerSemaphore(s *uint32, loops int, cdone chan bool) {
+	for i := 0; i < loops; i++ {
+		Runtime_Semacquire(s)
+		Runtime_Semrelease(s, false, 0)
+	}
+	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++ {
+		if i%3 == 0 {
+			if m.TryLock() {
+				m.Unlock()
+			}
+			continue
+		}
+		m.Lock()
+		m.Unlock()
+	}
+	cdone <- true
+}
+
+func TestMutex(t *testing.T) {
+	if n := runtime.SetMutexProfileFraction(1); n != 0 {
+		t.Logf("got mutexrate %d expected 0", n)
+	}
+	defer runtime.SetMutexProfileFraction(0)
+
+	m := new(Mutex)
+
+	m.Lock()
+	if m.TryLock() {
+		t.Fatalf("TryLock succeeded with mutex locked")
+	}
+	m.Unlock()
+	if !m.TryLock() {
+		t.Fatalf("TryLock failed with mutex unlocked")
+	}
+	m.Unlock()
+
+	c := make(chan bool)
+	for i := 0; i < 10; i++ {
+		go HammerMutex(m, 1000, c)
+	}
+	for i := 0; i < 10; i++ {
+		<-c
+	}
+}
+
+var misuseTests = []struct {
+	name string
+	f    func()
+}{
+	{
+		"Mutex.Unlock",
+		func() {
+			var mu Mutex
+			mu.Unlock()
+		},
+	},
+	{
+		"Mutex.Unlock2",
+		func() {
+			var mu Mutex
+			mu.Lock()
+			mu.Unlock()
+			mu.Unlock()
+		},
+	},
+	{
+		"RWMutex.Unlock",
+		func() {
+			var mu RWMutex
+			mu.Unlock()
+		},
+	},
+	{
+		"RWMutex.Unlock2",
+		func() {
+			var mu RWMutex
+			mu.RLock()
+			mu.Unlock()
+		},
+	},
+	{
+		"RWMutex.Unlock3",
+		func() {
+			var mu RWMutex
+			mu.Lock()
+			mu.Unlock()
+			mu.Unlock()
+		},
+	},
+	{
+		"RWMutex.RUnlock",
+		func() {
+			var mu RWMutex
+			mu.RUnlock()
+		},
+	},
+	{
+		"RWMutex.RUnlock2",
+		func() {
+			var mu RWMutex
+			mu.Lock()
+			mu.RUnlock()
+		},
+	},
+	{
+		"RWMutex.RUnlock3",
+		func() {
+			var mu RWMutex
+			mu.RLock()
+			mu.RUnlock()
+			mu.RUnlock()
+		},
+	},
+}
+
+func init() {
+	if len(os.Args) == 3 && os.Args[1] == "TESTMISUSE" {
+		for _, test := range misuseTests {
+			if test.name == os.Args[2] {
+				func() {
+					defer func() { recover() }()
+					test.f()
+				}()
+				fmt.Printf("test completed\n")
+				os.Exit(0)
+			}
+		}
+		fmt.Printf("unknown test\n")
+		os.Exit(0)
+	}
+}
+
+func TestMutexMisuse(t *testing.T) {
+	testenv.MustHaveExec(t)
+	for _, test := range misuseTests {
+		out, err := exec.Command(os.Args[0], "TESTMISUSE", test.name).CombinedOutput()
+		if err == nil || !strings.Contains(string(out), "unlocked") {
+			t.Errorf("%s: did not find failure with message about unlocked lock: %s\n%s\n", test.name, err, out)
+		}
+	}
+}
+
+func TestMutexFairness(t *testing.T) {
+	var mu Mutex
+	stop := make(chan bool)
+	defer close(stop)
+	go func() {
+		for {
+			mu.Lock()
+			time.Sleep(100 * time.Microsecond)
+			mu.Unlock()
+			select {
+			case <-stop:
+				return
+			default:
+			}
+		}
+	}()
+	done := make(chan bool, 1)
+	go func() {
+		for i := 0; i < 10; i++ {
+			time.Sleep(100 * time.Microsecond)
+			mu.Lock()
+			mu.Unlock()
+		}
+		done <- true
+	}()
+	select {
+	case <-done:
+	case <-time.After(10 * time.Second):
+		t.Fatalf("can't acquire Mutex in 10 seconds")
+	}
+}
+
+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]++
+			}
+		}
+	})
+}