ringbuffer: eliminate idle load by using condition variables instead of sleeps

pkg/ringbuffer/event.go

@@ -0,0 +1,38 @@
+package ringbuffer
+
+import (
+	"sync"
+)
+
+type event struct {
+	mutex sync.Mutex
+	cond  *sync.Cond
+	value bool
+}
+
+func newEvent() *event {
+	cv := &event{}
+	cv.cond = sync.NewCond(&cv.mutex)
+	return cv
+}
+
+func (cv *event) signal() {
+	func() {
+		cv.mutex.Lock()
+		defer cv.mutex.Unlock()
+		cv.value = true
+	}()
+
+	cv.cond.Broadcast()
+}
+
+func (cv *event) wait() {
+	cv.mutex.Lock()
+	defer cv.mutex.Unlock()
+
+	if !cv.value {
+		cv.cond.Wait()
+	}
+
+	cv.value = false
+}

pkg/ringbuffer/ringbuffer.go

@@ -2,7 +2,6 @@ package ringbuffer
 
 import (
 	"sync/atomic"
-	"time"
 	"unsafe"
 )
 
@@ -13,6 +12,7 @@ type RingBuffer struct {
 	writeIndex uint64
 	closed     int64
 	buffer     []unsafe.Pointer
+	event      *event
 }
 
 // New allocates a RingBuffer.
@@ -22,12 +22,14 @@ func New(size uint64) *RingBuffer {
 		readIndex:  1,
 		writeIndex: 0,
 		buffer:     make([]unsafe.Pointer, size),
+		event:      newEvent(),
 	}
 }
 
 // Close makes Pull() return false.
 func (r *RingBuffer) Close() {
 	atomic.StoreInt64(&r.closed, 1)
+	r.event.signal()
 }
 
 // Reset restores Pull().
@@ -45,6 +47,7 @@ func (r *RingBuffer) Push(data interface{}) {
 	writeIndex := atomic.AddUint64(&r.writeIndex, 1)
 	i := writeIndex % r.bufferSize
 	atomic.SwapPointer(&r.buffer[i], unsafe.Pointer(&data))
+	r.event.signal()
 }
 
 // Pull pulls some data from the beginning of the buffer.
@@ -57,7 +60,7 @@ func (r *RingBuffer) Pull() (interface{}, bool) {
 		i := r.readIndex % r.bufferSize
 		res := (*interface{})(atomic.SwapPointer(&r.buffer[i], nil))
 		if res == nil {
-			time.Sleep(10 * time.Millisecond)
+			r.event.wait()
 			continue
 		}
 

pkg/ringbuffer/ringbuffer_test.go

@@ -42,6 +42,22 @@ func TestPullBeforePush(t *testing.T) {
 	<-done
 }
 
+func TestClose(t *testing.T) {
+	r := New(1024)
+
+	done := make(chan struct{})
+	go func() {
+		defer close(done)
+		_, ok := r.Pull()
+		require.Equal(t, false, ok)
+	}()
+
+	time.Sleep(100 * time.Millisecond)
+
+	r.Close()
+	<-done
+}
+
 func BenchmarkPushPullContinuous(b *testing.B) {
 	r := New(1024 * 8)
 	defer r.Close()

testimages/rtsp-simple-server/Dockerfile

@@ -3,9 +3,8 @@ FROM amd64/golang:1.15-alpine3.12 AS server
 
 RUN apk --no-cache add git
 
-RUN git clone https://github.com/aler9/rtsp-simple-server
-
-RUN cd rtsp-simple-server \
+RUN git clone -b v0.14.2 https://github.com/aler9/rtsp-simple-server \
+    && cd rtsp-simple-server \
     && CGO_ENABLED=0 \
     go build -o /rtsp-simple-server .