gob: keep free lists of encoder and decoder states.

Avoids 3 mallocs in a round trip encoding/decoding a struct.

R=rsc, rsc1
CC=golang-dev
https://golang.org/cl/4278052

5 files changed, 86 insertions, 40 deletions

diff --git a/src/pkg/gob/codec_test.go b/src/pkg/gob/codec_test.go
index 4562e19309..e4364e6fd7 100644
--- a/src/pkg/gob/codec_test.go
+++ b/src/pkg/gob/codec_test.go
@@ -50,7 +50,7 @@ func testError(t *testing.T) {
 func TestUintCodec(t *testing.T) {
 	defer testError(t)
 	b := new(bytes.Buffer)
-	encState := newEncoderState(nil, b)
+	encState := newEncoderState(b)
 	for _, tt := range encodeT {
 		b.Reset()
 		encState.encodeUint(tt.x)
@@ -58,7 +58,7 @@ func TestUintCodec(t *testing.T) {
 			t.Errorf("encodeUint: %#x encode: expected % x got % x", tt.x, tt.b, b.Bytes())
 		}
 	}
-	decState := newDecodeState(nil, b)
+	decState := newDecodeState(b)
 	for u := uint64(0); ; u = (u + 1) * 7 {
 		b.Reset()
 		encState.encodeUint(u)
@@ -75,9 +75,9 @@ func TestUintCodec(t *testing.T) {
 func verifyInt(i int64, t *testing.T) {
 	defer testError(t)
 	var b = new(bytes.Buffer)
-	encState := newEncoderState(nil, b)
+	encState := newEncoderState(b)
 	encState.encodeInt(i)
-	decState := newDecodeState(nil, b)
+	decState := newDecodeState(b)
 	decState.buf = make([]byte, 8)
 	j := decState.decodeInt()
 	if i != j {
@@ -111,9 +111,16 @@ var complexResult = []byte{0x07, 0xFE, 0x31, 0x40, 0xFE, 0x33, 0x40}
 // The result of encoding "hello" with field number 7
 var bytesResult = []byte{0x07, 0x05, 'h', 'e', 'l', 'l', 'o'}
 
-func newencoderState(b *bytes.Buffer) *encoderState {
+func newDecodeState(buf *bytes.Buffer) *decoderState {
+	d := new(decoderState)
+	d.b = buf
+	d.buf = make([]byte, uint64Size)
+	return d
+}
+
+func newEncoderState(b *bytes.Buffer) *encoderState {
 	b.Reset()
-	state := newEncoderState(nil, b)
+	state := &encoderState{enc: nil, b: b}
 	state.fieldnum = -1
 	return state
 }
@@ -127,7 +134,7 @@ func TestScalarEncInstructions(t *testing.T) {
 	{
 		data := struct{ a bool }{true}
 		instr := &encInstr{encBool, 6, 0, 0}
-		state := newencoderState(b)
+		state := newEncoderState(b)
 		instr.op(instr, state, unsafe.Pointer(&data))
 		if !bytes.Equal(boolResult, b.Bytes()) {
 			t.Errorf("bool enc instructions: expected % x got % x", boolResult, b.Bytes())
@@ -139,7 +146,7 @@ func TestScalarEncInstructions(t *testing.T) {
 		b.Reset()
 		data := struct{ a int }{17}
 		instr := &encInstr{encInt, 6, 0, 0}
-		state := newencoderState(b)
+		state := newEncoderState(b)
 		instr.op(instr, state, unsafe.Pointer(&data))
 		if !bytes.Equal(signedResult, b.Bytes()) {
 			t.Errorf("int enc instructions: expected % x got % x", signedResult, b.Bytes())
@@ -151,7 +158,7 @@ func TestScalarEncInstructions(t *testing.T) {
 		b.Reset()
 		data := struct{ a uint }{17}
 		instr := &encInstr{encUint, 6, 0, 0}
-		state := newencoderState(b)
+		state := newEncoderState(b)
 		instr.op(instr, state, unsafe.Pointer(&data))
 		if !bytes.Equal(unsignedResult, b.Bytes()) {
 			t.Errorf("uint enc instructions: expected % x got % x", unsignedResult, b.Bytes())
@@ -163,7 +170,7 @@ func TestScalarEncInstructions(t *testing.T) {
 		b.Reset()
 		data := struct{ a int8 }{17}
 		instr := &encInstr{encInt8, 6, 0, 0}
-		state := newencoderState(b)
+		state := newEncoderState(b)
 		instr.op(instr, state, unsafe.Pointer(&data))
 		if !bytes.Equal(signedResult, b.Bytes()) {
 			t.Errorf("int8 enc instructions: expected % x got % x", signedResult, b.Bytes())
@@ -175,7 +182,7 @@ func TestScalarEncInstructions(t *testing.T) {
 		b.Reset()
 		data := struct{ a uint8 }{17}
 		instr := &encInstr{encUint8, 6, 0, 0}
-		state := newencoderState(b)
+		state := newEncoderState(b)
 		instr.op(instr, state, unsafe.Pointer(&data))
 		if !bytes.Equal(unsignedResult, b.Bytes()) {
 			t.Errorf("uint8 enc instructions: expected % x got % x", unsignedResult, b.Bytes())
@@ -187,7 +194,7 @@ func TestScalarEncInstructions(t *testing.T) {
 		b.Reset()
 		data := struct{ a int16 }{17}
 		instr := &encInstr{encInt16, 6, 0, 0}
-		state := newencoderState(b)
+		state := newEncoderState(b)
 		instr.op(instr, state, unsafe.Pointer(&data))
 		if !bytes.Equal(signedResult, b.Bytes()) {
 			t.Errorf("int16 enc instructions: expected % x got % x", signedResult, b.Bytes())
@@ -199,7 +206,7 @@ func TestScalarEncInstructions(t *testing.T) {
 		b.Reset()
 		data := struct{ a uint16 }{17}
 		instr := &encInstr{encUint16, 6, 0, 0}
-		state := newencoderState(b)
+		state := newEncoderState(b)
 		instr.op(instr, state, unsafe.Pointer(&data))
 		if !bytes.Equal(unsignedResult, b.Bytes()) {
 			t.Errorf("uint16 enc instructions: expected % x got % x", unsignedResult, b.Bytes())
@@ -211,7 +218,7 @@ func TestScalarEncInstructions(t *testing.T) {
 		b.Reset()
 		data := struct{ a int32 }{17}
 		instr := &encInstr{encInt32, 6, 0, 0}
-		state := newencoderState(b)
+		state := newEncoderState(b)
 		instr.op(instr, state, unsafe.Pointer(&data))
 		if !bytes.Equal(signedResult, b.Bytes()) {
 			t.Errorf("int32 enc instructions: expected % x got % x", signedResult, b.Bytes())
@@ -223,7 +230,7 @@ func TestScalarEncInstructions(t *testing.T) {
 		b.Reset()
 		data := struct{ a uint32 }{17}
 		instr := &encInstr{encUint32, 6, 0, 0}
-		state := newencoderState(b)
+		state := newEncoderState(b)
 		instr.op(instr, state, unsafe.Pointer(&data))
 		if !bytes.Equal(unsignedResult, b.Bytes()) {
 			t.Errorf("uint32 enc instructions: expected % x got % x", unsignedResult, b.Bytes())
@@ -235,7 +242,7 @@ func TestScalarEncInstructions(t *testing.T) {
 		b.Reset()
 		data := struct{ a int64 }{17}
 		instr := &encInstr{encInt64, 6, 0, 0}
-		state := newencoderState(b)
+		state := newEncoderState(b)
 		instr.op(instr, state, unsafe.Pointer(&data))
 		if !bytes.Equal(signedResult, b.Bytes()) {
 			t.Errorf("int64 enc instructions: expected % x got % x", signedResult, b.Bytes())
@@ -247,7 +254,7 @@ func TestScalarEncInstructions(t *testing.T) {
 		b.Reset()
 		data := struct{ a uint64 }{17}
 		instr := &encInstr{encUint64, 6, 0, 0}
-		state := newencoderState(b)
+		state := newEncoderState(b)
 		instr.op(instr, state, unsafe.Pointer(&data))
 		if !bytes.Equal(unsignedResult, b.Bytes()) {
 			t.Errorf("uint64 enc instructions: expected % x got % x", unsignedResult, b.Bytes())
@@ -259,7 +266,7 @@ func TestScalarEncInstructions(t *testing.T) {
 		b.Reset()
 		data := struct{ a float32 }{17}
 		instr := &encInstr{encFloat32, 6, 0, 0}
-		state := newencoderState(b)
+		state := newEncoderState(b)
 		instr.op(instr, state, unsafe.Pointer(&data))
 		if !bytes.Equal(floatResult, b.Bytes()) {
 			t.Errorf("float32 enc instructions: expected % x got % x", floatResult, b.Bytes())
@@ -271,7 +278,7 @@ func TestScalarEncInstructions(t *testing.T) {
 		b.Reset()
 		data := struct{ a float64 }{17}
 		instr := &encInstr{encFloat64, 6, 0, 0}
-		state := newencoderState(b)
+		state := newEncoderState(b)
 		instr.op(instr, state, unsafe.Pointer(&data))
 		if !bytes.Equal(floatResult, b.Bytes()) {
 			t.Errorf("float64 enc instructions: expected % x got % x", floatResult, b.Bytes())
@@ -283,7 +290,7 @@ func TestScalarEncInstructions(t *testing.T) {
 		b.Reset()
 		data := struct{ a []byte }{[]byte("hello")}
 		instr := &encInstr{encUint8Array, 6, 0, 0}
-		state := newencoderState(b)
+		state := newEncoderState(b)
 		instr.op(instr, state, unsafe.Pointer(&data))
 		if !bytes.Equal(bytesResult, b.Bytes()) {
 			t.Errorf("bytes enc instructions: expected % x got % x", bytesResult, b.Bytes())
@@ -295,7 +302,7 @@ func TestScalarEncInstructions(t *testing.T) {
 		b.Reset()
 		data := struct{ a string }{"hello"}
 		instr := &encInstr{encString, 6, 0, 0}
-		state := newencoderState(b)
+		state := newEncoderState(b)
 		instr.op(instr, state, unsafe.Pointer(&data))
 		if !bytes.Equal(bytesResult, b.Bytes()) {
 			t.Errorf("string enc instructions: expected % x got % x", bytesResult, b.Bytes())
@@ -315,7 +322,7 @@ func execDec(typ string, instr *decInstr, state *decoderState, t *testing.T, p u
 
 func newDecodeStateFromData(data []byte) *decoderState {
 	b := bytes.NewBuffer(data)
-	state := newDecodeState(nil, b)
+	state := newDecodeState(b)
 	state.fieldnum = -1
 	return state
 }
diff --git a/src/pkg/gob/decode.go b/src/pkg/gob/decode.go
index c47fea1a70..d00ef7cd65 100644
--- a/src/pkg/gob/decode.go
+++ b/src/pkg/gob/decode.go
@@ -31,18 +31,29 @@ type decoderState struct {
 	b        *bytes.Buffer
 	fieldnum int // the last field number read.
 	buf      []byte
+	next     *decoderState // for free list
 }
 
 // We pass the bytes.Buffer separately for easier testing of the infrastructure
 // without requiring a full Decoder.
-func newDecodeState(dec *Decoder, buf *bytes.Buffer) *decoderState {
-	d := new(decoderState)
-	d.dec = dec
+func (dec *Decoder) newDecoderState(buf *bytes.Buffer) *decoderState {
+	d := dec.freeList
+	if d == nil {
+		d = new(decoderState)
+		d.dec = dec
+	} else {
+		dec.freeList = d.next
+	}
 	d.b = buf
 	d.buf = make([]byte, uint64Size)
 	return d
 }
 
+func (dec *Decoder) freeDecoderState(d *decoderState) {
+	d.next = dec.freeList
+	dec.freeList = d
+}
+
 func overflow(name string) os.ErrorString {
 	return os.ErrorString(`value for "` + name + `" out of range`)
 }
@@ -445,7 +456,7 @@ func (dec *Decoder) decodeSingle(engine *decEngine, ut *userTypeInfo, p uintptr)
 		indir = int(ut.decIndir)
 	}
 	p = allocate(ut.base, p, indir)
-	state := newDecodeState(dec, &dec.buf)
+	state := dec.newDecoderState(&dec.buf)
 	state.fieldnum = singletonField
 	basep := p
 	delta := int(state.decodeUint())
@@ -458,6 +469,7 @@ func (dec *Decoder) decodeSingle(engine *decEngine, ut *userTypeInfo, p uintptr)
 		ptr = decIndirect(ptr, instr.indir)
 	}
 	instr.op(instr, state, ptr)
+	dec.freeDecoderState(state)
 	return nil
 }
 
@@ -468,7 +480,7 @@ func (dec *Decoder) decodeSingle(engine *decEngine, ut *userTypeInfo, p uintptr)
 // from the user's value, not from the innards of an engine.
 func (dec *Decoder) decodeStruct(engine *decEngine, ut *userTypeInfo, p uintptr, indir int) (err os.Error) {
 	p = allocate(ut.base.(*reflect.StructType), p, indir)
-	state := newDecodeState(dec, &dec.buf)
+	state := dec.newDecoderState(&dec.buf)
 	state.fieldnum = -1
 	basep := p
 	for state.b.Len() > 0 {
@@ -492,12 +504,13 @@ func (dec *Decoder) decodeStruct(engine *decEngine, ut *userTypeInfo, p uintptr,
 		instr.op(instr, state, p)
 		state.fieldnum = fieldnum
 	}
+	dec.freeDecoderState(state)
 	return nil
 }
 
 // ignoreStruct discards the data for a struct with no destination.
 func (dec *Decoder) ignoreStruct(engine *decEngine) (err os.Error) {
-	state := newDecodeState(dec, &dec.buf)
+	state := dec.newDecoderState(&dec.buf)
 	state.fieldnum = -1
 	for state.b.Len() > 0 {
 		delta := int(state.decodeUint())
@@ -515,13 +528,14 @@ func (dec *Decoder) ignoreStruct(engine *decEngine) (err os.Error) {
 		instr.op(instr, state, unsafe.Pointer(nil))
 		state.fieldnum = fieldnum
 	}
+	dec.freeDecoderState(state)
 	return nil
 }
 
 // ignoreSingle discards the data for a top-level non-struct value with no
 // destination. It's used when calling Decode with a nil value.
 func (dec *Decoder) ignoreSingle(engine *decEngine) (err os.Error) {
-	state := newDecodeState(dec, &dec.buf)
+	state := dec.newDecoderState(&dec.buf)
 	state.fieldnum = singletonField
 	delta := int(state.decodeUint())
 	if delta != 0 {
@@ -529,6 +543,7 @@ func (dec *Decoder) ignoreSingle(engine *decEngine) (err os.Error) {
 	}
 	instr := &engine.instr[singletonField]
 	instr.op(instr, state, unsafe.Pointer(nil))
+	dec.freeDecoderState(state)
 	return nil
 }
 
diff --git a/src/pkg/gob/decoder.go b/src/pkg/gob/decoder.go
index 0c5fbbd7ea..5e5afb37b4 100644
--- a/src/pkg/gob/decoder.go
+++ b/src/pkg/gob/decoder.go
@@ -22,7 +22,7 @@ type Decoder struct {
 	wireType     map[typeId]*wireType                    // map from remote ID to local description
 	decoderCache map[reflect.Type]map[typeId]**decEngine // cache of compiled engines
 	ignorerCache map[typeId]**decEngine                  // ditto for ignored objects
-	countState   *decoderState                           // reads counts from wire
+	freeList     *decoderState                           // list of free decoderStates; avoids reallocation
 	countBuf     []byte                                  // used for decoding integers while parsing messages
 	tmp          []byte                                  // temporary storage for i/o; saves reallocating
 	err          os.Error
diff --git a/src/pkg/gob/encode.go b/src/pkg/gob/encode.go
index adaf958e78..4dbafdddeb 100644
--- a/src/pkg/gob/encode.go
+++ b/src/pkg/gob/encode.go
@@ -25,10 +25,26 @@ type encoderState struct {
 	sendZero bool                 // encoding an array element or map key/value pair; send zero values
 	fieldnum int                  // the last field number written.
 	buf      [1 + uint64Size]byte // buffer used by the encoder; here to avoid allocation.
+	next     *encoderState        // for free list
 }
 
-func newEncoderState(enc *Encoder, b *bytes.Buffer) *encoderState {
-	return &encoderState{enc: enc, b: b}
+func (enc *Encoder) newEncoderState(b *bytes.Buffer) *encoderState {
+	e := enc.freeList
+	if e == nil {
+		e = new(encoderState)
+		e.enc = enc
+	} else {
+		enc.freeList = e.next
+	}
+	e.sendZero = false
+	e.fieldnum = 0
+	e.b = b
+	return e
+}
+
+func (enc *Encoder) freeEncoderState(e *encoderState) {
+	e.next = enc.freeList
+	enc.freeList = e
 }
 
 // Unsigned integers have a two-state encoding.  If the number is less
@@ -326,7 +342,7 @@ const singletonField = 0
 
 // encodeSingle encodes a single top-level non-struct value.
 func (enc *Encoder) encodeSingle(b *bytes.Buffer, engine *encEngine, basep uintptr) {
-	state := newEncoderState(enc, b)
+	state := enc.newEncoderState(b)
 	state.fieldnum = singletonField
 	// There is no surrounding struct to frame the transmission, so we must
 	// generate data even if the item is zero.  To do this, set sendZero.
@@ -339,11 +355,12 @@ func (enc *Encoder) encodeSingle(b *bytes.Buffer, engine *encEngine, basep uintp
 		}
 	}
 	instr.op(instr, state, p)
+	enc.freeEncoderState(state)
 }
 
 // encodeStruct encodes a single struct value.
 func (enc *Encoder) encodeStruct(b *bytes.Buffer, engine *encEngine, basep uintptr) {
-	state := newEncoderState(enc, b)
+	state := enc.newEncoderState(b)
 	state.fieldnum = -1
 	for i := 0; i < len(engine.instr); i++ {
 		instr := &engine.instr[i]
@@ -355,11 +372,12 @@ func (enc *Encoder) encodeStruct(b *bytes.Buffer, engine *encEngine, basep uintp
 		}
 		instr.op(instr, state, p)
 	}
+	enc.freeEncoderState(state)
 }
 
 // encodeArray encodes the array whose 0th element is at p.
 func (enc *Encoder) encodeArray(b *bytes.Buffer, p uintptr, op encOp, elemWid uintptr, elemIndir int, length int) {
-	state := newEncoderState(enc, b)
+	state := enc.newEncoderState(b)
 	state.fieldnum = -1
 	state.sendZero = true
 	state.encodeUint(uint64(length))
@@ -375,6 +393,7 @@ func (enc *Encoder) encodeArray(b *bytes.Buffer, p uintptr, op encOp, elemWid ui
 		op(nil, state, unsafe.Pointer(elemp))
 		p += uintptr(elemWid)
 	}
+	enc.freeEncoderState(state)
 }
 
 // encodeReflectValue is a helper for maps. It encodes the value v.
@@ -392,7 +411,7 @@ func encodeReflectValue(state *encoderState, v reflect.Value, op encOp, indir in
 // Because map internals are not exposed, we must use reflection rather than
 // addresses.
 func (enc *Encoder) encodeMap(b *bytes.Buffer, mv *reflect.MapValue, keyOp, elemOp encOp, keyIndir, elemIndir int) {
-	state := newEncoderState(enc, b)
+	state := enc.newEncoderState(b)
 	state.fieldnum = -1
 	state.sendZero = true
 	keys := mv.Keys()
@@ -401,6 +420,7 @@ func (enc *Encoder) encodeMap(b *bytes.Buffer, mv *reflect.MapValue, keyOp, elem
 		encodeReflectValue(state, key, keyOp, keyIndir)
 		encodeReflectValue(state, mv.Elem(key), elemOp, elemIndir)
 	}
+	enc.freeEncoderState(state)
 }
 
 // encodeInterface encodes the interface value iv.
@@ -409,7 +429,7 @@ func (enc *Encoder) encodeMap(b *bytes.Buffer, mv *reflect.MapValue, keyOp, elem
 // by the concrete value.  A nil value gets sent as the empty string for the name,
 // followed by no value.
 func (enc *Encoder) encodeInterface(b *bytes.Buffer, iv *reflect.InterfaceValue) {
-	state := newEncoderState(enc, b)
+	state := enc.newEncoderState(b)
 	state.fieldnum = -1
 	state.sendZero = true
 	if iv.IsNil() {
@@ -445,6 +465,7 @@ func (enc *Encoder) encodeInterface(b *bytes.Buffer, iv *reflect.InterfaceValue)
 	if enc.err != nil {
 		error(err)
 	}
+	enc.freeEncoderState(state)
 }
 
 // encGobEncoder encodes a value that implements the GobEncoder interface.
@@ -456,10 +477,11 @@ func (enc *Encoder) encodeGobEncoder(b *bytes.Buffer, v reflect.Value, index int
 	if err != nil {
 		error(err)
 	}
-	state := newEncoderState(enc, b)
+	state := enc.newEncoderState(b)
 	state.fieldnum = -1
 	state.encodeUint(uint64(len(data)))
 	state.b.Write(data)
+	enc.freeEncoderState(state)
 }
 
 var encOpTable = [...]encOp{
diff --git a/src/pkg/gob/encoder.go b/src/pkg/gob/encoder.go
index 228445ff81..7045e8e892 100644
--- a/src/pkg/gob/encoder.go
+++ b/src/pkg/gob/encoder.go
@@ -19,6 +19,7 @@ type Encoder struct {
 	w          []io.Writer             // where to send the data
 	sent       map[reflect.Type]typeId // which types we've already sent
 	countState *encoderState           // stage for writing counts
+	freeList   *encoderState           // list of free encoderStates; avoids reallocation
 	buf        []byte                  // for collecting the output.
 	err        os.Error
 }
@@ -28,7 +29,7 @@ func NewEncoder(w io.Writer) *Encoder {
 	enc := new(Encoder)
 	enc.w = []io.Writer{w}
 	enc.sent = make(map[reflect.Type]typeId)
-	enc.countState = newEncoderState(enc, new(bytes.Buffer))
+	enc.countState = enc.newEncoderState(new(bytes.Buffer))
 	return enc
 }
 
@@ -218,7 +219,7 @@ func (enc *Encoder) EncodeValue(value reflect.Value) os.Error {
 	}
 
 	enc.err = nil
-	state := newEncoderState(enc, new(bytes.Buffer))
+	state := enc.newEncoderState(new(bytes.Buffer))
 
 	enc.sendTypeDescriptor(enc.writer(), state, ut)
 	enc.sendTypeId(state, ut)
@@ -234,5 +235,6 @@ func (enc *Encoder) EncodeValue(value reflect.Value) os.Error {
 		enc.writeMessage(enc.writer(), state.b)
 	}
 
+	enc.freeEncoderState(state)
 	return enc.err
 }