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,
+	}
+}