Implement a lock based ring buffer for internal/buffer. (#3377)

internal/buffer/buffer.go

@@ -14,9 +14,12 @@ var (
 
 // Buffer is an object for storing metrics in a circular buffer.
 type Buffer struct {
-	buf chan telegraf.Metric
-
-	mu sync.Mutex
+	sync.Mutex
+	buf   []telegraf.Metric
+	first int
+	last  int
+	size  int
+	empty bool
 }
 
 // NewBuffer returns a Buffer
@@ -24,47 +27,98 @@ type Buffer struct {
 //   called when the buffer is full, then the oldest metric(s) will be dropped.
 func NewBuffer(size int) *Buffer {
 	return &Buffer{
-		buf: make(chan telegraf.Metric, size),
+		buf:   make([]telegraf.Metric, size),
+		first: 0,
+		last:  0,
+		size:  size,
+		empty: true,
 	}
 }
 
 // IsEmpty returns true if Buffer is empty.
 func (b *Buffer) IsEmpty() bool {
-	return len(b.buf) == 0
+	return b.empty
 }
 
 // Len returns the current length of the buffer.
 func (b *Buffer) Len() int {
-	return len(b.buf)
+	if b.empty {
+		return 0
+	} else if b.first <= b.last {
+		return b.last - b.first + 1
+	}
+	// Spans the end of array.
+	// size - gap in the middle
+	return b.size - (b.first - b.last - 1) // size - gap
+}
+
+func (b *Buffer) push(m telegraf.Metric) {
+	// Empty
+	if b.empty {
+		b.last = b.first // Reset
+		b.buf[b.last] = m
+		b.empty = false
+		return
+	}
+
+	b.last++
+	b.last %= b.size
+
+	// Full
+	if b.first == b.last {
+		MetricsDropped.Incr(1)
+		b.first = (b.first + 1) % b.size
+	}
+	b.buf[b.last] = m
 }
 
 // Add adds metrics to the buffer.
 func (b *Buffer) Add(metrics ...telegraf.Metric) {
-	b.mu.Lock()
-	for i, _ := range metrics {
+	b.Lock()
+	defer b.Unlock()
+	for i := range metrics {
 		MetricsWritten.Incr(1)
-		select {
-		case b.buf <- metrics[i]:
-		default:
-			MetricsDropped.Incr(1)
-			<-b.buf
-			b.buf <- metrics[i]
-		}
+		b.push(metrics[i])
 	}
-	b.mu.Unlock()
 }
 
 // Batch returns a batch of metrics of size batchSize.
 // the batch will be of maximum length batchSize. It can be less than batchSize,
 // if the length of Buffer is less than batchSize.
 func (b *Buffer) Batch(batchSize int) []telegraf.Metric {
-	b.mu.Lock()
-	n := min(len(b.buf), batchSize)
-	out := make([]telegraf.Metric, n)
-	for i := 0; i < n; i++ {
-		out[i] = <-b.buf
+	b.Lock()
+	defer b.Unlock()
+	outLen := min(b.Len(), batchSize)
+	out := make([]telegraf.Metric, outLen)
+	if outLen == 0 {
+		return out
+	}
+
+	// We copy everything right of first up to last, count or end
+	// b.last >= rightInd || b.last < b.first
+	// therefore wont copy past b.last
+	rightInd := min(b.size, b.first+outLen) - 1
+
+	copyCount := copy(out, b.buf[b.first:rightInd+1])
+
+	// We've emptied the ring
+	if rightInd == b.last {
+		b.empty = true
+	}
+	b.first = rightInd + 1
+	b.first %= b.size
+
+	// We circle back for the rest
+	if copyCount < outLen {
+		right := min(b.last, outLen-copyCount)
+		copy(out[copyCount:], b.buf[b.first:right+1])
+		// We've emptied the ring
+		if right == b.last {
+			b.empty = true
+		}
+		b.first = right + 1
+		b.first %= b.size
 	}
-	b.mu.Unlock()
 	return out
 }
 

internal/buffer/buffer_test.go

@@ -1,6 +1,8 @@
 package buffer
 
 import (
+	"sync"
+	"sync/atomic"
 	"testing"
 
 	"github.com/influxdata/telegraf"
@@ -17,6 +19,107 @@ var metricList = []telegraf.Metric{
 	testutil.TestMetric(8, "mymetric5"),
 }
 
+func makeBench5(b *testing.B, freq, batchSize int) {
+	const k = 1000
+	var wg sync.WaitGroup
+	buf := NewBuffer(10000)
+	m := testutil.TestMetric(1, "mymetric")
+
+	for i := 0; i < b.N; i++ {
+		buf.Add(m, m, m, m, m)
+		if i%(freq*k) == 0 {
+			wg.Add(1)
+			go func() {
+				buf.Batch(batchSize * k)
+				wg.Done()
+			}()
+		}
+	}
+	// Flush
+	buf.Batch(b.N)
+	wg.Wait()
+
+}
+func makeBenchStrict(b *testing.B, freq, batchSize int) {
+	const k = 1000
+	var count uint64
+	var wg sync.WaitGroup
+	buf := NewBuffer(10000)
+	m := testutil.TestMetric(1, "mymetric")
+
+	for i := 0; i < b.N; i++ {
+		buf.Add(m)
+		if i%(freq*k) == 0 {
+			wg.Add(1)
+			go func() {
+				defer wg.Done()
+				l := len(buf.Batch(batchSize * k))
+				atomic.AddUint64(&count, uint64(l))
+			}()
+		}
+	}
+	// Flush
+	wg.Add(1)
+	go func() {
+		l := len(buf.Batch(b.N))
+		atomic.AddUint64(&count, uint64(l))
+		wg.Done()
+	}()
+
+	wg.Wait()
+	if count != uint64(b.N) {
+		b.Errorf("not all metrics came out. %d of %d", count, b.N)
+	}
+}
+func makeBench(b *testing.B, freq, batchSize int) {
+	const k = 1000
+	var wg sync.WaitGroup
+	buf := NewBuffer(10000)
+	m := testutil.TestMetric(1, "mymetric")
+
+	for i := 0; i < b.N; i++ {
+		buf.Add(m)
+		if i%(freq*k) == 0 {
+			wg.Add(1)
+			go func() {
+				buf.Batch(batchSize * k)
+				wg.Done()
+			}()
+		}
+	}
+	wg.Wait()
+	// Flush
+	buf.Batch(b.N)
+}
+
+func BenchmarkBufferBatch5Add(b *testing.B) {
+	makeBench5(b, 100, 101)
+}
+func BenchmarkBufferBigInfrequentBatchCatchup(b *testing.B) {
+	makeBench(b, 100, 101)
+}
+func BenchmarkBufferOftenBatch(b *testing.B) {
+	makeBench(b, 1, 1)
+}
+func BenchmarkBufferAlmostBatch(b *testing.B) {
+	makeBench(b, 10, 9)
+}
+func BenchmarkBufferSlowBatch(b *testing.B) {
+	makeBench(b, 10, 1)
+}
+func BenchmarkBufferBatchNoDrop(b *testing.B) {
+	makeBenchStrict(b, 1, 4)
+}
+func BenchmarkBufferCatchup(b *testing.B) {
+	buf := NewBuffer(10000)
+	m := testutil.TestMetric(1, "mymetric")
+
+	for i := 0; i < b.N; i++ {
+		buf.Add(m)
+	}
+	buf.Batch(b.N)
+}
+
 func BenchmarkAddMetrics(b *testing.B) {
 	buf := NewBuffer(10000)
 	m := testutil.TestMetric(1, "mymetric")