Bugfix: conditional variable broadcast channel size (#3906)

* Conditional variable broadcast function should create channel with size 1, not 0

Author: wxing1292

common/locks/condition_variable_impl.go

@@ -46,7 +46,7 @@ func NewConditionVariable(
 		lock: lock,
 
 		chanLock: sync.Mutex{},
-		channel:  make(chan struct{}, 1),
+		channel:  newCVChannel(),
 	}
 }
 
@@ -64,7 +64,7 @@ func (c *ConditionVariableImpl) Signal() {
 
 // Broadcast wakes all goroutines waiting on this condition variable.
 func (c *ConditionVariableImpl) Broadcast() {
-	newChannel := make(chan struct{})
+	newChannel := newCVChannel()
 
 	c.chanLock.Lock()
 	defer c.chanLock.Unlock()
@@ -104,3 +104,7 @@ func (c *ConditionVariableImpl) Wait(
 		// interrupted
 	}
 }
+
+func newCVChannel() chan struct{} {
+	return make(chan struct{}, 1)
+}

common/locks/condition_variable_test.go

@@ -40,7 +40,7 @@ type (
 		suite.Suite
 
 		lock sync.Locker
-		cv   ConditionVariable
+		cv   *ConditionVariableImpl
 	}
 )
 
@@ -67,6 +67,34 @@ func (s *conditionVariableSuite) TearDownTest() {
 
 }
 
+func (s *conditionVariableSuite) TestChannelSize_New() {
+	s.testChannelSize(s.cv.channel)
+}
+
+func (s *conditionVariableSuite) TestChannelSize_Broadcast() {
+	s.cv.Broadcast()
+	s.testChannelSize(s.cv.channel)
+}
+
+func (s *conditionVariableSuite) testChannelSize(
+	channel chan struct{},
+) {
+	// assert channel size == 1
+	select {
+	case channel <- struct{}{}:
+		// noop
+	default:
+		s.Fail("conditional variable size should be 1")
+	}
+
+	select {
+	case channel <- struct{}{}:
+		s.Fail("conditional variable size should be 1")
+	default:
+		// noop
+	}
+}
+
 func (s *conditionVariableSuite) TestSignal() {
 	signalWaitGroup := sync.WaitGroup{}
 	signalWaitGroup.Add(1)