Semaphore pattern

09-semaphore-pattern/semaphore.go

@@ -0,0 +1,52 @@
+package semaphore
+
+import (
+	"errors"
+	"time"
+)
+
+/*
+	核心思想：
+		1.type interface 包含Acquire和release行为
+		2.定义结构体， 包含chan 和过期时间属性
+		3. 在Acquire中实现channel读入
+		4. 在release中channel 读出， 阻塞超时返回错误
+*/
+var (
+	ErrNoTickets = errors.New("semaphore: could not acquire semaphore")
+	ErrIllegalRelease = errors.New("semaphore: can't release semaphore without acquiring it first")
+)
+type Interface interface {
+	Acquire() error
+	Release() error
+}
+//定义结构体， 信号量使用chan struct{}
+type Semaphore struct {
+	sem chan struct{}
+	timeout time.Duration
+}
+
+func (s *Semaphore) Acquire() error {
+	select {
+	case s.sem <- struct{}{}:
+		return nil
+	case <- time.After(s.timeout):
+		return ErrNoTickets
+	}
+}
+
+func (s *Semaphore) Release() error {
+	select {
+	case <- s.sem:
+		return nil
+	case <- time.After(s.timeout):
+		return ErrIllegalRelease
+	}
+}
+
+func New(tickets int, timeout time.Duration) Interface {
+	return &Semaphore{
+		sem:     make(chan struct{}, tickets),
+		timeout: timeout,
+	}
+}

09-semaphore-pattern/semaphore_test.go

@@ -0,0 +1,34 @@
+package semaphore
+
+import (
+	"fmt"
+	"testing"
+	"time"
+)
+
+func TestNoRelease(t *testing.T) {
+	ticket, timeout := 1, 2*time.Second
+	sem := New(ticket, timeout)
+
+	if err := sem.Acquire(); err != nil {
+		fmt.Println(err)
+	}
+
+	if err := sem.Release(); err != nil {
+		fmt.Println(err)
+	}
+	if err := sem.Release(); err != nil {
+		fmt.Println(err)
+	}
+}
+
+func TestNoTicket(t *testing.T) {
+	ticket, timeout := 0, 1 * time.Second
+	sem := New(ticket, timeout)
+
+	if err := sem.Acquire(); err != nil {
+		if err == ErrNoTickets {
+			fmt.Println(err)
+		}
+	}
+}

main.go

@@ -16,6 +16,17 @@ func main() {
 	}
 	fmt.Println("jie")
 
-	var m struct{}
-	m = P{}
+	//type sem chan struct{}
+	s := make(chan struct{}, 1)
+	select {
+	case s <- struct{}{}:
+		fmt.Println("struct")
+	}
+
+	type sem chan struct{}
+	m := make(sem, 1)
+	select {
+	case m <- struct{}{}:
+		fmt.Println("struct1")
+	}
 }