From 87db8356b3cfea728585dcc9b0b8394b0e228266 Mon Sep 17 00:00:00 2001
From: Tamer Tas <contact@tmrts.com>
Date: Mon, 4 Jan 2016 06:15:29 +0200
Subject: [PATCH] Update semaphore pattern

---
 semaphore.go => semaphore/semaphore.go | 28 +++++++++++++-----------
 semaphore/semaphore_test.go            | 30 ++++++++++++++++++++++++++
 2 files changed, 46 insertions(+), 12 deletions(-)
 rename semaphore.go => semaphore/semaphore.go (60%)
 create mode 100644 semaphore/semaphore_test.go

diff --git a/semaphore.go b/semaphore/semaphore.go
similarity index 60%
rename from semaphore.go
rename to semaphore/semaphore.go
index 766e76f..585cd11 100644
--- a/semaphore.go
+++ b/semaphore/semaphore.go
@@ -10,24 +10,19 @@ var (
 	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 semaphore struct {
+type implementation struct {
 	sem     chan struct{}
 	timeout time.Duration
 }
 
-func New(tickets int, timeout time.Duration) Semaphore {
-	return &semaphore{
-		sem:     make(chan struct{}, tickets),
-		timeout: timeout,
-	}
-}
-
-func (s *semaphore) Acquire() error {
+func (s *implementation) Acquire() error {
 	select {
 	case s.sem <- struct{}{}:
 		return nil
@@ -36,11 +31,20 @@ func (s *semaphore) Acquire() error {
 	}
 }
 
-func (s *semaphore) Release() error {
-	_, ok := <-s.sem
-	if !ok {
+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,
+	}
+}
diff --git a/semaphore/semaphore_test.go b/semaphore/semaphore_test.go
new file mode 100644
index 0000000..0ca2226
--- /dev/null
+++ b/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)
+	}
+}