Fix case when released more then acquired.

semaphore.go

@@ -137,19 +137,25 @@ func (s *semaphore) TryAcquire(n int) bool {
 	}
 
 	for {
+		// get current semaphore count and limit
 		state := atomic.LoadUint64(&s.state)
 		count := state & 0xFFFFFFFF
 		limit := state >> 32
+
+		// new count
 		newCount := count + uint64(n)
+
 		if newCount <= limit {
 			if atomic.CompareAndSwapUint64(&s.state, state, limit<<32+newCount) {
+				// acquired
 				return true
 			}
 
 			// CAS failed, try again
 			continue
 		}
 
+		// semaphore is full
 		return false
 	}
 }
@@ -159,13 +165,18 @@ func (s *semaphore) Release(n int) int {
 		panic("n must be positive number")
 	}
 	for {
+		// get current semaphore count and limit
 		state := atomic.LoadUint64(&s.state)
 		count := state & 0xFFFFFFFF
 		limit := state >> 32
-		if count == 0 {
+
+		if count < uint64(n) {
 			panic("semaphore release without acquire")
 		}
+
+		// new count
 		newCount := count - uint64(n)
+
 		if atomic.CompareAndSwapUint64(&s.state, state, state&0xFFFFFFFF00000000+newCount) {
 
 			// notifying possible waiters only if there weren't free slots before
@@ -179,6 +190,7 @@ func (s *semaphore) Release(n int) int {
 				// send broadcast signal
 				close(oldBroadcastCh)
 			}
+
 			return int(count)
 		}
 	}

semaphore_test.go

@@ -198,6 +198,18 @@ func TestSemaphore_Release_without_Acquire_panic_expected(t *testing.T) {
 	sem.Release(1)
 }
 
+func TestSemaphore_Release_more_than_Acquired_panic_expected(t *testing.T) {
+	sem := New(1)
+
+	defer func() {
+		if recover() == nil {
+			t.Error("Panic expected")
+		}
+	}()
+	sem.Acquire(context.Background(), 1)
+	sem.Release(2)
+}
+
 func TestSemaphore_Acquire_2_times_Release_2_times(t *testing.T) {
 	sem := New(2)
 	checkLimitAndCount(t, sem, 2, 0)