add semaphore

This commit is contained in:
siddontang 2015-03-31 21:40:50 +08:00
parent dfa1fad4a1
commit 530a231625
2 changed files with 106 additions and 0 deletions

65
sync2/semaphore.go Normal file
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@ -0,0 +1,65 @@
package sync2
import (
"sync"
"sync/atomic"
"time"
)
func NewSemaphore(initialCount int) *Semaphore {
res := &Semaphore{
counter: int64(initialCount),
}
res.cond.L = &res.lock
return res
}
type Semaphore struct {
lock sync.Mutex
cond sync.Cond
counter int64
}
func (s *Semaphore) Release() {
s.lock.Lock()
s.counter += 1
if s.counter >= 0 {
s.cond.Signal()
}
s.lock.Unlock()
}
func (s *Semaphore) Acquire() {
s.lock.Lock()
for s.counter < 1 {
s.cond.Wait()
}
s.counter -= 1
s.lock.Unlock()
}
func (s *Semaphore) AcquireTimeout(timeout time.Duration) bool {
done := make(chan bool, 1)
// Gate used to communicate between the threads and decide what the result
// is. If the main thread decides, we have timed out, otherwise we succeed.
decided := new(int32)
go func() {
s.Acquire()
if atomic.SwapInt32(decided, 1) == 0 {
done <- true
} else {
// If we already decided the result, and this thread did not win
s.Release()
}
}()
select {
case <-done:
return true
case <-time.NewTimer(timeout).C:
if atomic.SwapInt32(decided, 1) == 1 {
// The other thread already decided the result
return true
}
return false
}
}

41
sync2/semaphore_test.go Normal file
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// Copyright 2012, Google Inc. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package sync2
import (
"testing"
"time"
)
func TestSemaNoTimeout(t *testing.T) {
s := NewSemaphore(1)
s.Acquire()
released := false
go func() {
time.Sleep(10 * time.Millisecond)
released = true
s.Release()
}()
s.Acquire()
if !released {
t.Errorf("want true, got false")
}
}
func TestSemaTimeout(t *testing.T) {
s := NewSemaphore(1)
s.Acquire()
go func() {
time.Sleep(10 * time.Millisecond)
s.Release()
}()
if ok := s.AcquireTimeout(5 * time.Millisecond); ok {
t.Errorf("want false, got true")
}
time.Sleep(10 * time.Millisecond)
if ok := s.AcquireTimeout(5 * time.Millisecond); !ok {
t.Errorf("want true, got false")
}
}