homework 13: fix additionally implemented TryLock and TryRLock

homeworks/13_sync_primitives/homework.go

@@ -22,7 +22,12 @@ func (m *RWMutex) Lock() {
 	m.mutex.Lock()
 	defer m.mutex.Unlock()
 
-	m.underLock()
+	m.writersWaiting++
+	for m.writerActive || m.readerCount != 0 {
+		m.writerCond.Wait()
+	}
+	m.writerActive = true
+	m.writersWaiting--
 }
 
 func (m *RWMutex) Unlock() {
@@ -36,7 +41,10 @@ func (m *RWMutex) RLock() {
 	m.mutex.Lock()
 	defer m.mutex.Unlock()
 
-	m.underRLock()
+	for m.writerActive || m.writersWaiting > 0 {
+		m.writerCond.Wait()
+	}
+	m.readerCount++
 }
 
 func (m *RWMutex) RUnlock() {
@@ -49,41 +57,25 @@ func (m *RWMutex) RUnlock() {
 }
 
 func (m *RWMutex) TryLock() bool {
-	ok := m.mutex.TryLock()
-	if !ok {
-		return false
-	}
+	m.mutex.Lock()
 	defer m.mutex.Unlock()
 
-	m.underLock()
+	if m.writerActive || m.readerCount > 0 {
+		return false
+	}
 
+	m.writerActive = true
 	return true
 }
 
 func (m *RWMutex) TryRLock() bool {
-	ok := m.mutex.TryLock()
-	if !ok {
-		return false
-	}
+	m.mutex.Lock()
 	defer m.mutex.Unlock()
 
-	m.underRLock()
-
-	return true
-}
-
-func (m *RWMutex) underLock() {
-	m.writersWaiting++
-	for m.writerActive || m.readerCount != 0 {
-		m.writerCond.Wait()
+	if m.writerActive || m.writersWaiting > 0 {
+		return false
 	}
-	m.writerActive = true
-	m.writersWaiting--
-}
 
-func (m *RWMutex) underRLock() {
-	for m.writerActive || m.writersWaiting > 0 {
-		m.writerCond.Wait()
-	}
 	m.readerCount++
+	return true
 }

homeworks/13_sync_primitives/homework_test.go

@@ -100,3 +100,39 @@ func TestRWMutexWithWriterPriority(t *testing.T) {
 	assert.True(t, mutualExlusionWithWriter.Load())
 	assert.Equal(t, int32(1), readersCount.Load())
 }
+
+func TestTryLockFailsWhenWriterActive(t *testing.T) {
+	mutex := NewRWMutex()
+	mutex.Lock() // writer
+
+	ok := mutex.TryLock()
+	assert.False(t, ok)
+}
+
+func TestTryLockFailsWhenReadersActive(t *testing.T) {
+	mutex := NewRWMutex()
+	mutex.RLock() // reader
+
+	ok := mutex.TryLock()
+	assert.False(t, ok)
+}
+
+func TestTryLockSucceedsWhenFree(t *testing.T) {
+	mutex := NewRWMutex()
+
+	ok := mutex.TryLock()
+	assert.True(t, ok)
+
+	var entered atomic.Bool
+	entered.Store(false)
+
+	go func() {
+		mutex.Lock()
+		entered.Store(true)
+	}()
+
+	time.Sleep(100 * time.Millisecond)
+	assert.False(t, entered.Load())
+
+	mutex.Unlock()
+}