Pool buffers used in S3.WriteStream

Signed-off-by: Stephen J Day <stephen.day@docker.com>

docs/storage/driver/s3/s3.go

@@ -22,6 +22,7 @@ import (
 	"net/http"
 	"strconv"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/AdRoll/goamz/aws"
@@ -72,6 +73,9 @@ type driver struct {
 	ChunkSize     int64
 	Encrypt       bool
 	RootDirectory string
+
+	pool  sync.Pool // pool []byte buffers used for WriteStream
+	zeros []byte    // shared, zero-valued buffer used for WriteStream
 }
 
 type baseEmbed struct {
@@ -224,6 +228,11 @@ func New(params DriverParameters) (*Driver, error) {
 		ChunkSize:     params.ChunkSize,
 		Encrypt:       params.Encrypt,
 		RootDirectory: params.RootDirectory,
+		zeros:         make([]byte, params.ChunkSize),
+	}
+
+	d.pool.New = func() interface{} {
+		return make([]byte, d.ChunkSize)
 	}
 
 	return &Driver{
@@ -287,8 +296,7 @@ func (d *driver) WriteStream(path string, offset int64, reader io.Reader) (total
 		return 0, err
 	}
 
-	buf := make([]byte, d.ChunkSize)
+	buf := d.getbuf()
-	zeroBuf := make([]byte, d.ChunkSize)
 
 	// We never want to leave a dangling multipart upload, our only consistent state is
 	// when there is a whole object at path. This is in order to remain consistent with
@@ -314,6 +322,8 @@ func (d *driver) WriteStream(path string, offset int64, reader io.Reader) (total
 				}
 			}
 		}
+
+		d.putbuf(buf) // needs to be here to pick up new buf value
 	}()
 
 	// Fills from 0 to total from current
@@ -367,6 +377,8 @@ func (d *driver) WriteStream(path string, offset int64, reader io.Reader) (total
 		}
 
 		go func(bytesRead int, from int64, buf []byte) {
+			defer d.putbuf(buf) // this buffer gets dropped after this call
+
 			// parts and partNumber are safe, because this function is the only one modifying them and we
 			// force it to be executed serially.
 			if bytesRead > 0 {
@@ -381,7 +393,7 @@ func (d *driver) WriteStream(path string, offset int64, reader io.Reader) (total
 			putErrChan <- nil
 		}(bytesRead, from, buf)
 
-		buf = make([]byte, d.ChunkSize)
+		buf = d.getbuf() // use a new buffer for the next call
 		return nil
 	}
 
@@ -429,7 +441,7 @@ func (d *driver) WriteStream(path string, offset int64, reader io.Reader) (total
 			fromZeroFillSmall := func(from, to int64) error {
 				bytesRead = 0
 				for from+int64(bytesRead) < to {
-					nn, err := bytes.NewReader(zeroBuf).Read(buf[from+int64(bytesRead) : to])
+					nn, err := bytes.NewReader(d.zeros).Read(buf[from+int64(bytesRead) : to])
 					bytesRead += nn
 					if err != nil {
 						return err
@@ -443,7 +455,7 @@ func (d *driver) WriteStream(path string, offset int64, reader io.Reader) (total
 			fromZeroFillLarge := func(from, to int64) error {
 				bytesRead64 := int64(0)
 				for to-(from+bytesRead64) >= d.ChunkSize {
-					part, err := multi.PutPart(int(partNumber), bytes.NewReader(zeroBuf))
+					part, err := multi.PutPart(int(partNumber), bytes.NewReader(d.zeros))
 					if err != nil {
 						return err
 					}
@@ -724,3 +736,13 @@ func getPermissions() s3.ACL {
 func (d *driver) getContentType() string {
 	return "application/octet-stream"
 }
+
+// getbuf returns a buffer from the driver's pool with length d.ChunkSize.
+func (d *driver) getbuf() []byte {
+	return d.pool.Get().([]byte)
+}
+
+func (d *driver) putbuf(p []byte) {
+	copy(p, d.zeros)
+	d.pool.Put(p)
+}