Update semaphore pattern

semaphore/semaphore.go

@@ -0,0 +1,50 @@
+package semaphore
+
+import (
+	"errors"
+	"time"
+)
+
+var (
+	ErrNoTickets      = errors.New("semaphore: could not aquire semaphore")
+	ErrIllegalRelease = errors.New("semaphore: can't release the semaphore without acquiring it first")
+)
+
+// Interface, typically a type, that satisfies semaphore.Interface
+// can be acquired and released.
+type Interface interface {
+	Acquire() error
+	Release() error
+}
+
+type implementation struct {
+	sem     chan struct{}
+	timeout time.Duration
+}
+
+func (s *implementation) Acquire() error {
+	select {
+	case s.sem <- struct{}{}:
+		return nil
+	case <-time.After(s.timeout):
+		return ErrNoTickets
+	}
+}
+
+func (s *implementation) Release() error {
+	select {
+	case _ = <-s.sem:
+		return nil
+	case <-time.After(s.timeout):
+		return ErrIllegalRelease
+	}
+
+	return nil
+}
+
+func New(tickets int, timeout time.Duration) Interface {
+	return &implementation{
+		sem:     make(chan struct{}, tickets),
+		timeout: timeout,
+	}
+}

semaphore/semaphore_test.go

@@ -0,0 +1,30 @@
+package semaphore_test
+
+import (
+	"testing"
+	"time"
+
+	"github.com/tmrts/go-patterns/semaphore"
+)
+
+func TestCreatesSemaphore(t *testing.T) {
+	tickets, timeout := 1, 3*time.Second
+	s := semaphore.New(tickets, timeout)
+
+	if err := s.Acquire(); err != nil {
+		t.Errorf("semaphore.Acquire() got errors %s", err)
+	}
+
+	if err := s.Release(); err != nil {
+		t.Errorf("semaphore.Release() got errors %s", err)
+	}
+}
+
+func TestCreatesNonBlockingSemaphore(t *testing.T) {
+	tickets, timeout := 0, 0
+	s := semaphore.New(tickets, timeout)
+
+	if err := s.Acquire(); err != semaphore.ErrIllegalRelease {
+		t.Errorf("non-blocking semaphore.Acquire() expected error %s got %s", semaphore.ErrIllegalRelease, err)
+	}
+}