add ability to resuse vellum builders

Change-Id: I18e2645afb3cec81633b600b2940cb479c24fdd9
Reviewed-on: http://review.couchbase.org/90248
Reviewed-by: Steve Yen <[email protected]>
Tested-by: Marty Schoch <[email protected]>

Author: mschoch

builder.go

@@ -67,6 +67,19 @@ func newBuilder(w io.Writer, opts *BuilderOpts) (*Builder, error) {
 	return rv, nil
 }
 
+func (b *Builder) Reset(w io.Writer) error {
+	b.unfinished.Reset()
+	b.registry.Reset()
+	b.lastAddr = noneAddr
+	b.encoder.reset(w)
+
+	err := b.encoder.start()
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
 // Insert the provided value to the set being built.
 // NOTE: values must be inserted in lexicographical order.
 func (b *Builder) Insert(key []byte, val uint64) error {
@@ -165,6 +178,13 @@ type unfinishedNodes struct {
 	cache []builderNodeUnfinished
 }
 
+func (u *unfinishedNodes) Reset() {
+	u.stack = u.stack[:0]
+	for i := 0; i < len(u.cache); i++ {
+		u.cache[i] = builderNodeUnfinished{}
+	}
+}
+
 func newUnfinishedNodes() *unfinishedNodes {
 	rv := &unfinishedNodes{
 		stack: make([]*builderNodeUnfinished, 0, 64),

encoder_v1.go

@@ -42,6 +42,10 @@ func newEncoderV1(w io.Writer) *encoderV1 {
 	}
 }
 
+func (e *encoderV1) reset(w io.Writer) {
+	e.bw.Reset(w)
+}
+
 func (e *encoderV1) start() error {
 	header := make([]byte, headerSize)
 	binary.LittleEndian.PutUint64(header, versionV1)

encoding.go

@@ -32,6 +32,7 @@ type encoder interface {
 	start() error
 	encodeState(s *builderNode, addr int) (int, error)
 	finish(count, rootAddr int) error
+	reset(w io.Writer)
 }
 
 func loadEncoder(ver int, w io.Writer) (encoder, error) {

registry.go

@@ -42,6 +42,13 @@ func newRegistry(tableSize, mruSize int) *registry {
 	return rv
 }
 
+func (r *registry) Reset() {
+	for i := 0; i < len(r.table); i++ {
+		r.table[i] = registryCell{}
+	}
+	r.hasher.Reset()
+}
+
 func (r *registry) entry(node *builderNode) (bool, int, *registryCell) {
 	if len(r.table) == 0 {
 		return false, 0, nil

writer.go

@@ -32,6 +32,11 @@ func newWriter(w io.Writer) *writer {
 	}
 }
 
+func (w *writer) Reset(newWriter io.Writer) {
+	w.w.Reset(newWriter)
+	w.counter = 0
+}
+
 func (w *writer) WriteByte(c byte) error {
 	err := w.w.WriteByte(c)
 	if err != nil {