Only serialise and compress reports once per publish.

experimental/demoprobe/main.go

@@ -27,10 +27,11 @@ func main() {
 	if err != nil {
 		log.Fatal(err)
 	}
+	rp := xfer.NewReportPublisher(publisher)
 
 	rand.Seed(time.Now().UnixNano())
 	for range time.Tick(*publishInterval) {
-		if err := publisher.Publish(demoReport(*hostCount)); err != nil {
+		if err := rp.Publish(demoReport(*hostCount)); err != nil {
 			log.Print(err)
 		}
 	}

experimental/fixprobe/main.go

@@ -39,7 +39,8 @@ func main() {
 		log.Fatal(err)
 	}
 
+	rp := xfer.NewReportPublisher(publisher)
 	for range time.Tick(*publishInterval) {
-		publisher.Publish(fixedReport)
+		rp.Publish(fixedReport)
 	}
 }

probe/main.go

@@ -175,6 +175,7 @@ func main() {
 			pubTick = time.Tick(*publishInterval)
 			spyTick = time.Tick(*spyInterval)
 			r       = report.MakeReport()
+			p       = xfer.NewReportPublisher(publishers)
 		)
 
 		for {
@@ -182,7 +183,7 @@ func main() {
 			case <-pubTick:
 				publishTicks.WithLabelValues().Add(1)
 				r.Window = *publishInterval
-				if err := publishers.Publish(r); err != nil {
+				if err := p.Publish(r); err != nil {
 					log.Printf("publish: %v", err)
 				}
 				r = report.MakeReport()

xfer/publisher.go

@@ -1,9 +1,6 @@
 package xfer
 
 import (
-	"bytes"
-	"compress/gzip"
-	"encoding/gob"
 	"fmt"
 	"log"
 	"net/http"
@@ -11,8 +8,6 @@ import (
 	"strings"
 	"sync"
 	"time"
-
-	"github.com/weaveworks/scope/report"
 )
 
 const (
@@ -22,7 +17,7 @@ const (
 
 // Publisher is something which can send a report to a remote collector.
 type Publisher interface {
-	Publish(report.Report) error
+	Publish(*Buffer) error
 	Stop()
 }
 
@@ -63,16 +58,10 @@ func (p HTTPPublisher) String() string {
 }
 
 // Publish publishes the report to the URL.
-func (p HTTPPublisher) Publish(rpt report.Report) error {
-	gzbuf := bytes.Buffer{}
-	gzwriter := gzip.NewWriter(&gzbuf)
+func (p HTTPPublisher) Publish(buf *Buffer) error {
+	defer buf.Put()
 
-	if err := gob.NewEncoder(gzwriter).Encode(rpt); err != nil {
-		return err
-	}
-	gzwriter.Close() // otherwise the content won't get flushed to the output stream
-
-	req, err := http.NewRequest("POST", p.url, &gzbuf)
+	req, err := http.NewRequest("POST", p.url, buf)
 	if err != nil {
 		return err
 	}
@@ -108,7 +97,7 @@ func AuthorizationHeader(token string) string {
 // concurrent publishes are dropped.
 type BackgroundPublisher struct {
 	publisher Publisher
-	reports   chan report.Report
+	reports   chan *Buffer
 	quit      chan struct{}
 }
 
@@ -116,7 +105,7 @@ type BackgroundPublisher struct {
 func NewBackgroundPublisher(p Publisher) *BackgroundPublisher {
 	result := &BackgroundPublisher{
 		publisher: p,
-		reports:   make(chan report.Report),
+		reports:   make(chan *Buffer),
 		quit:      make(chan struct{}),
 	}
 	go result.loop()
@@ -146,9 +135,9 @@ func (b *BackgroundPublisher) loop() {
 }
 
 // Publish implements Publisher
-func (b *BackgroundPublisher) Publish(r report.Report) error {
+func (b *BackgroundPublisher) Publish(buf *Buffer) error {
 	select {
-	case b.reports <- r:
+	case b.reports <- buf:
 	default:
 	}
 	return nil
@@ -198,13 +187,18 @@ func (p *MultiPublisher) Add(target string) {
 }
 
 // Publish implements Publisher by emitting the report to all publishers.
-func (p *MultiPublisher) Publish(rpt report.Report) error {
+func (p *MultiPublisher) Publish(buf *Buffer) error {
 	p.mtx.RLock()
 	defer p.mtx.RUnlock()
 
+	// First take a reference for each publisher
+	for range p.m {
+		buf.Get()
+	}
+
 	var errs []string
 	for _, publisher := range p.m {
-		if err := publisher.Publish(rpt); err != nil {
+		if err := publisher.Publish(buf); err != nil {
 			errs = append(errs, err.Error())
 		}
 	}

xfer/publisher_test.go

@@ -64,7 +64,8 @@ func TestHTTPPublisher(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	if err := p.Publish(rpt); err != nil {
+	rp := xfer.NewReportPublisher(p)
+	if err := rp.Publish(rpt); err != nil {
 		t.Error(err)
 	}
 
@@ -83,7 +84,7 @@ func TestMultiPublisher(t *testing.T) {
 	)
 
 	multiPublisher.Add("first")
-	if err := multiPublisher.Publish(report.MakeReport()); err != nil {
+	if err := multiPublisher.Publish(xfer.NewBuffer(nil)); err != nil {
 		t.Error(err)
 	}
 	if want, have := 1, p.count; want != have {
@@ -91,7 +92,7 @@ func TestMultiPublisher(t *testing.T) {
 	}
 
 	multiPublisher.Add("second") // but factory returns same mockPublisher
-	if err := multiPublisher.Publish(report.MakeReport()); err != nil {
+	if err := multiPublisher.Publish(xfer.NewBuffer(nil)); err != nil {
 		t.Error(err)
 	}
 	if want, have := 3, p.count; want != have {
@@ -101,5 +102,5 @@ func TestMultiPublisher(t *testing.T) {
 
 type mockPublisher struct{ count int }
 
-func (p *mockPublisher) Publish(report.Report) error { p.count++; return nil }
-func (p *mockPublisher) Stop()                       {}
+func (p *mockPublisher) Publish(*xfer.Buffer) error { p.count++; return nil }
+func (p *mockPublisher) Stop()                      {}

xfer/report_publisher.go

@@ -0,0 +1,79 @@
+package xfer
+
+import (
+	"bytes"
+	"compress/gzip"
+	"encoding/gob"
+	"sync"
+	"sync/atomic"
+
+	"github.com/weaveworks/scope/report"
+)
+
+// A Buffer is a reference counted bytes.Buffer, which belongs
+// to a sync.Pool
+type Buffer struct {
+	bytes.Buffer
+	pool *sync.Pool
+	refs int32
+}
+
+// NewBuffer creates a new buffer
+func NewBuffer(pool *sync.Pool) *Buffer {
+	return &Buffer{
+		pool: pool,
+		refs: 0,
+	}
+}
+
+// Get increases the reference count.  It is safe for concurrent calls.
+func (b *Buffer) Get() {
+	atomic.AddInt32(&b.refs, 1)
+}
+
+// Put decreases the reference count, and when it hits zero, puts the
+// buffer back in the pool.
+func (b *Buffer) Put() {
+	if atomic.AddInt32(&b.refs, -1) == 0 {
+		b.Reset()
+		b.pool.Put(b)
+	}
+}
+
+// NewBufferPool creates a new buffer pool.
+func NewBufferPool() *sync.Pool {
+	result := &sync.Pool{}
+	result.New = func() interface{} {
+		return NewBuffer(result)
+	}
+	return result
+}
+
+// A ReportPublisher uses a buffer pool to serialise reports, which it
+// then passes to a publisher
+type ReportPublisher struct {
+	buffers   *sync.Pool
+	publisher Publisher
+}
+
+// NewReportPublisher creates a new report publisher
+func NewReportPublisher(publisher Publisher) *ReportPublisher {
+	return &ReportPublisher{
+		buffers:   NewBufferPool(),
+		publisher: publisher,
+	}
+}
+
+// Publish serialises and compresses a report, then passes it to a publisher
+func (p *ReportPublisher) Publish(r report.Report) error {
+	buf := p.buffers.Get().(*Buffer)
+	gzwriter := gzip.NewWriter(buf)
+	if err := gob.NewEncoder(gzwriter).Encode(r); err != nil {
+		buf.Reset()
+		p.buffers.Put(buf)
+		return err
+	}
+	gzwriter.Close() // otherwise the content won't get flushed to the output stream
+
+	return p.publisher.Publish(buf)
+}