diff --git a/go.sum b/go.sum
index 95f3e70..84eb062 100644
--- a/go.sum
+++ b/go.sum
@@ -8,6 +8,7 @@ github.com/kylelemons/godebug v0.0.0-20170820004349-d65d576e9348 h1:MtvEpTB6LX3v
 github.com/kylelemons/godebug v0.0.0-20170820004349-d65d576e9348/go.mod h1:B69LEHPfb2qLo0BaaOLcbitczOKLWTsrBG9LczfCD4k=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0 h1:4G4v2dO3VZwixGIRoQ5Lfboy6nUhCyYzaqnIAPPhYs4=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.5.1 h1:nOGnQDM7FYENwehXlg/kFVnos3rEvtKTjRvOWSzb6H4=
 github.com/stretchr/testify v1.5.1/go.mod h1:5W2xD1RspED5o8YsWQXVCued0rvSQ+mT+I5cxcmMvtA=
diff --git a/internal/lockserver/lockserver.go b/internal/lockserver/lockserver.go
index 0ecc49c..a8599b0 100644
--- a/internal/lockserver/lockserver.go
+++ b/internal/lockserver/lockserver.go
@@ -38,7 +38,7 @@ func (s *Service) HealthCheck(ip string, counter *int) error {
 }
 
 // CheckAcquire returns nil if the file is acquired
-func (s *Service) CheckAcquire(fileID string) error {
+func (s *Service) CheckAcquire(fileID string, counter *float32) error {
 	lockMap.Mutex.Lock()
 	if lockMap.LockMap[fileID] {
 		lockMap.Mutex.Unlock()
@@ -62,7 +62,7 @@ func (s *Service) Acquire(fileID string, counter *float32) error {
 }
 
 // CheckRelease returns nil if the file is released
-func (s *Service) CheckRelease(fileID string) error {
+func (s *Service) CheckRelease(fileID string, counter *float32) error {
 	lockMap.Mutex.Lock()
 	if lockMap.LockMap[fileID] {
 		lockMap.Mutex.Unlock()
@@ -74,6 +74,7 @@ func (s *Service) CheckRelease(fileID string) error {
 
 // Release lets a client to release a lock on an object.
 func (s *Service) Release(fileID string, counter *float32) error {
+	fmt.Println("WE")
 	lockMap.Mutex.Lock()
 	if lockMap.LockMap[fileID] {
 		delete(lockMap.LockMap, fileID)
diff --git a/internal/lockserver/lockserver_test.go b/internal/lockserver/lockserver_test.go
index 0521149..63c63a1 100644
--- a/internal/lockserver/lockserver_test.go
+++ b/internal/lockserver/lockserver_test.go
@@ -65,12 +65,145 @@ func TestSingleLockAndRelease1(t *testing.T) {
 	if err != nil {
 		assert.Fail(fmt.Sprintf("Failed to acquire lock: %v", err))
 	}
+	result := client.Call("Service.CheckAcquire", "1", &y)
+	if result != nil {
+		assert.Fail(fmt.Sprintf("Lock was not acquired"))
+	}
 
 	err = client.Call("Service.Release", "1", &y)
 
 	if err != nil {
 		assert.Fail(fmt.Sprintf("Failed to release lock: %v", err))
 	}
+
+	result = client.Call("Service.CheckRelease", "1", &y)
+	if result != nil {
+		assert.Fail(fmt.Sprintf("Lock was not released"))
+	}
+
+	err = client.Call("Service.Acquire", "1", &y)
+
+	if err != nil {
+		assert.Fail(fmt.Sprintf("Failed to acquire lock: %v", err))
+	}
+
+	result = client.Call("Service.CheckAcquire", "1", &y)
+	if result != nil {
+		assert.Fail(fmt.Sprintf("Lock was not acquired"))
+	}
+
+	err = client.Call("Service.Release", "1", &y)
+	if err != nil {
+		assert.Fail(fmt.Sprintf("Failed to release lock: %v", err))
+	}
+
+	result = client.Call("Service.CheckRelease", "1", &y)
+	if result != nil {
+		assert.Fail(fmt.Sprintf("Lock was not released"))
+	}
+
+	shutdownSignal <- os.Kill
+	timer1 = time.NewTimer(5 * time.Millisecond)
+	<-timer1.C
+}
+
+func TestMultipleLockAndRelease(t *testing.T) {
+	t.Logf("acquire a acquire b release b release a\n")
+	shutdownSignal := make(chan os.Signal, 1)
+	go StartServer(shutdownSignal)
+
+	timer1 := time.NewTimer(5 * time.Millisecond)
+	<-timer1.C
+
+	assert := assert.New(t)
+	client, err := rpc.DialHTTP("tcp", "localhost:55550")
+
+	var y float32
+	y = 3.4
+	if err != nil {
+		log.Fatal("Connection error: ", err)
+	}
+	err = client.Call("Service.Acquire", "1", &y)
+
+	if err != nil {
+		assert.Fail(fmt.Sprintf("Failed to acquire lock: %v", err))
+	}
+
+	result := client.Call("Service.CheckAcquire", "1", &y)
+	if result != nil {
+		assert.Fail(fmt.Sprintf("Lock was not acquired"))
+	}
+
+	err = client.Call("Service.Acquire", "2", &y)
+	if err != nil {
+		assert.Fail(fmt.Sprintf("Failed to release lock: %v", err))
+	}
+
+	result = client.Call("Service.CheckAcquire", "2", &y)
+	if result != nil {
+		assert.Fail(fmt.Sprintf("Lock was not acquired"))
+	}
+
+	err = client.Call("Service.Release", "2", &y)
+	if err != nil {
+		assert.Fail(fmt.Sprintf("Failed to release lock: %v", err))
+	}
+	result = client.Call("Service.CheckRelease", "2", &y)
+	if result != nil {
+		assert.Fail(fmt.Sprintf("Lock was not released"))
+	}
+
+	err = client.Call("Service.Release", "1", &y)
+	if err != nil {
+		assert.Fail(fmt.Sprintf("Failed to release lock: %v", err))
+	}
+	result = client.Call("Service.CheckRelease", "1", &y)
+	if result != nil {
+		assert.Fail(fmt.Sprintf("Lock was not released"))
+	}
+
+	shutdownSignal <- os.Kill
+	timer1 = time.NewTimer(5 * time.Millisecond)
+	<-timer1.C
+}
+
+func TestConcurrentRoutinesAcquiringSameLock(t *testing.T) {
+	shutdownSignal := make(chan os.Signal, 1)
+	go StartServer(shutdownSignal)
+
+	timer1 := time.NewTimer(5 * time.Millisecond)
+	<-timer1.C
+
+	client, err := rpc.DialHTTP("tcp", "localhost:55550")
+	var y float32
+	y = 3.4
+
+	for i := 0; i < 5; i++ {
+		go func(t *testing.T, tid int) {
+			assert := assert.New(t)
+			t.Logf("client %d acquire a release a", tid)
+			err = client.Call("Service.Release", "1", &y)
+			if err != nil {
+				assert.Fail(fmt.Sprintf("Failed to release lock: %v", err))
+			}
+			t.Logf("client %d acquire done", tid)
+			result := client.Call("Service.CheckAcquire", "1", &y)
+			if result != nil {
+				assert.Fail(fmt.Sprintf("Lock was not acquired"))
+			}
+			time.Sleep(1)
+			t.Logf("client %d release", tid)
+			err = client.Call("Service.Release", "1", &y)
+			if err != nil {
+				assert.Fail(fmt.Sprintf("Failed to release lock: %v", err))
+			}
+			result = client.Call("Service.CheckRelease", "1", &y)
+			if result != nil {
+				assert.Fail(fmt.Sprintf("Lock was not released"))
+			}
+			t.Logf("client %d release done", tid)
+		}(t, i)
+	}
 	shutdownSignal <- os.Kill
 	timer1 = time.NewTimer(5 * time.Millisecond)
 	<-timer1.C