WIP

bson/default_value_encoders.go

@@ -17,7 +17,11 @@ import (
 	"go.mongodb.org/mongo-driver/x/bsonx/bsoncore"
 )
 
-var bvwPool = NewValueWriterPool()
+var bvwPool = sync.Pool{
+	New: func() interface{} {
+		return new(valueWriter)
+	},
+}
 
 var errInvalidValue = errors.New("cannot encode invalid element")
 
@@ -511,7 +515,9 @@ func codeWithScopeEncodeValue(ec EncodeContext, vw ValueWriter, val reflect.Valu
 	defer sliceWriterPool.Put(sw)
 	*sw = (*sw)[:0]
 
-	scopeVW := bvwPool.Get(sw)
+	scopeVW := bvwPool.Get().(*valueWriter)
+	scopeVW.reset(scopeVW.buf[:0])
+	scopeVW.w = sw
 	defer bvwPool.Put(scopeVW)
 
 	encoder, err := ec.LookupEncoder(reflect.TypeOf(cws.Scope))

bson/marshal.go

@@ -96,8 +96,26 @@ func MarshalValue(val interface{}) (Type, []byte, error) {
 // Deprecated: Using a custom registry to marshal individual BSON values will not be supported in Go
 // Driver 2.0.
 func MarshalValueWithRegistry(r *Registry, val interface{}) (Type, []byte, error) {
-	sw := sliceWriter(make([]byte, 0))
-	vw := bvwPool.Get(&sw).(*valueWriter)
+	sw := bufPool.Get().(*bytes.Buffer)
+	defer func() {
+		// Proper usage of a sync.Pool requires each entry to have approximately
+		// the same memory cost. To obtain this property when the stored type
+		// contains a variably-sized buffer, we add a hard limit on the maximum
+		// buffer to place back in the pool. We limit the size to 16MiB because
+		// that's the maximum wire message size supported by any current MongoDB
+		// server.
+		//
+		// Comment based on
+		// https://cs.opensource.google/go/go/+/refs/tags/go1.19:src/fmt/print.go;l=147
+		//
+		// Recycle byte slices that are smaller than 16MiB and at least half
+		// occupied.
+		if sw.Cap() < 16*1024*1024 && sw.Cap()/2 < sw.Len() {
+			bufPool.Put(sw)
+		}
+	}()
+	sw.Reset()
+	vw := NewValueWriter(sw).(*valueWriter)
 	vwFlusher, err := vw.WriteDocumentElement("")
 	if err != nil {
 		return 0, nil, err
@@ -107,7 +125,7 @@ func MarshalValueWithRegistry(r *Registry, val interface{}) (Type, []byte, error
 	enc := encPool.Get().(*Encoder)
 	defer encPool.Put(enc)
 	enc.Reset(vwFlusher)
-	enc.ec = EncodeContext{Registry: r}
+	enc.SetRegistry(r)
 	if err := enc.Encode(val); err != nil {
 		return 0, nil, err
 	}
@@ -118,7 +136,8 @@ func MarshalValueWithRegistry(r *Registry, val interface{}) (Type, []byte, error
 	if err := vw.Flush(); err != nil {
 		return 0, nil, err
 	}
-	return Type(sw[0]), sw[2:], nil
+	buf := sw.Bytes()
+	return Type(buf[0]), buf[2:], nil
 }
 
 // MarshalExtJSON returns the extended JSON encoding of val.

bson/value_writer.go

@@ -33,53 +33,6 @@ func putValueWriter(vw *valueWriter) {
 	}
 }
 
-// ValueWriterPool is a pool for BSON ValueWriters.
-//
-// Deprecated: ValueWriterPool will not be supported in Go Driver 2.0.
-type ValueWriterPool struct {
-	pool sync.Pool
-}
-
-// NewValueWriterPool creates a new pool for ValueWriter instances that write to BSON.
-//
-// Deprecated: ValueWriterPool will not be supported in Go Driver 2.0.
-func NewValueWriterPool() *ValueWriterPool {
-	return &ValueWriterPool{
-		pool: sync.Pool{
-			New: func() interface{} {
-				return new(valueWriter)
-			},
-		},
-	}
-}
-
-// Get retrieves a BSON ValueWriter from the pool and resets it to use w as the destination.
-//
-// Deprecated: ValueWriterPool will not be supported in Go Driver 2.0.
-func (bvwp *ValueWriterPool) Get(w io.Writer) ValueWriter {
-	vw := bvwp.pool.Get().(*valueWriter)
-
-	// TODO: Having to call reset here with the same buffer doesn't really make sense.
-	vw.reset(vw.buf)
-	vw.buf = vw.buf[:0]
-	vw.w = w
-	return vw
-}
-
-// Put inserts a ValueWriter into the pool. If the ValueWriter is not a BSON ValueWriter, nothing
-// happens and ok will be false.
-//
-// Deprecated: ValueWriterPool will not be supported in Go Driver 2.0.
-func (bvwp *ValueWriterPool) Put(vw ValueWriter) (ok bool) {
-	bvw, ok := vw.(*valueWriter)
-	if !ok {
-		return false
-	}
-
-	bvwp.pool.Put(bvw)
-	return true
-}
-
 // This is here so that during testing we can change it and not require
 // allocating a 4GB slice.
 var maxSize = math.MaxInt32

mongo/mongo.go

@@ -52,17 +52,14 @@ func (me MarshalError) Error() string {
 //	}
 type Pipeline []bson.D
 
-// bvwPool is a pool of BSON value writers. BSON value writers
-var bvwPool = bson.NewValueWriterPool()
-
 // getEncoder takes a writer, BSON options, and a BSON registry and returns a properly configured
 // bson.Encoder that writes to the given writer.
 func getEncoder(
 	w io.Writer,
 	opts *options.BSONOptions,
 	reg *bson.Registry,
 ) (*bson.Encoder, error) {
-	vw := bvwPool.Get(w)
+	vw := bson.NewValueWriter(w)
 	enc := bson.NewEncoder(vw)
 
 	if opts != nil {