internal/impl: add MessageState to every generated message
We define MessageState, which is essentially an atomically set *MessageInfo.
By nesting this as the first field in every generated message, we can
implement the reflective methods on a *MessageState when obtained by
unsafe casting a concrete message pointer as a *MessageState.
The MessageInfo held by MessageState provides additional Go type information
to interpret the memory that comes after the contents of the MessageState.
Since we are nesting a MessageState in every message,
the memory use of every message instance grows by 8B.
On average, the body of ProtoReflect grows from 133B to 202B (+50%).
However, this is offset by XXX_Methods, which is 108B and
will be removed in a future CL. Taking into account the eventual removal
of XXX_Methods, this is a net reduction of 25%.
name old time/op new time/op delta
Name/Value-4 70.3ns ± 2% 17.5ns ± 6% -75.08% (p=0.000 n=10+10)
Name/Nil-4 70.6ns ± 3% 33.4ns ± 2% -52.66% (p=0.000 n=10+10)
name old alloc/op new alloc/op delta
Name/Value-4 16.0B ± 0% 0.0B -100.00% (p=0.000 n=10+10)
Name/Nil-4 16.0B ± 0% 0.0B -100.00% (p=0.000 n=10+10)
name old allocs/op new allocs/op delta
Name/Value-4 1.00 ± 0% 0.00 -100.00% (p=0.000 n=10+10)
Name/Nil-4 1.00 ± 0% 0.00 -100.00% (p=0.000 n=10+10)
Change-Id: I92bd58dc681c57c92612fd5ba7fc066aea34e95a
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/185460
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/internal/impl/message_reflect.go b/internal/impl/message_reflect.go
new file mode 100644
index 0000000..a9eb7a9
--- /dev/null
+++ b/internal/impl/message_reflect.go
@@ -0,0 +1,220 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package impl
+
+import (
+ "fmt"
+ "reflect"
+
+ "google.golang.org/protobuf/internal/pragma"
+ pvalue "google.golang.org/protobuf/internal/value"
+ pref "google.golang.org/protobuf/reflect/protoreflect"
+ piface "google.golang.org/protobuf/runtime/protoiface"
+)
+
+// MessageState is a data structure that is nested as the first field in a
+// concrete message. It provides a way to implement the ProtoReflect method
+// in an allocation-free way without needing to have a shadow Go type generated
+// for every message type. This technique only works using unsafe.
+//
+//
+// Example generated code:
+//
+// type M struct {
+// state protoimpl.MessageState
+//
+// Field1 int32
+// Field2 string
+// Field3 *BarMessage
+// ...
+// }
+//
+// func (m *M) ProtoReflect() protoreflect.Message {
+// mi := &file_fizz_buzz_proto_msgInfos[5]
+// if protoimpl.UnsafeEnabled && m != nil {
+// ms := protoimpl.X.MessageStateOf(Pointer(m))
+// if ms.LoadMessageInfo() == nil {
+// ms.StoreMessageInfo(mi)
+// }
+// return ms
+// }
+// return mi.MessageOf(m)
+// }
+//
+// The MessageState type holds a *MessageInfo, which must be atomically set to
+// the message info associated with a given message instance.
+// By unsafely converting a *M into a *MessageState, the MessageState object
+// has access to all the information needed to implement protobuf reflection.
+// It has access to the message info as its first field, and a pointer to the
+// MessageState is identical to a pointer to the concrete message value.
+//
+//
+// Requirements:
+// • The type M must implement protoreflect.ProtoMessage.
+// • The address of m must not be nil.
+// • The address of m and the address of m.state must be equal,
+// even though they are different Go types.
+type MessageState struct {
+ pragma.NoUnkeyedLiterals
+ pragma.DoNotCompare
+ pragma.DoNotCopy
+
+ mi *MessageInfo
+}
+
+type messageState MessageState
+
+var (
+ _ pref.Message = (*messageState)(nil)
+ _ pvalue.Unwrapper = (*messageState)(nil)
+)
+
+// messageDataType is a tuple of a pointer to the message data and
+// a pointer to the message type. It is a generalized way of providing a
+// reflective view over a message instance. The disadvantage of this approach
+// is the need to allocate this tuple of 16B.
+type messageDataType struct {
+ p pointer
+ mi *MessageInfo
+}
+
+type (
+ messageIfaceWrapper messageDataType
+ messageReflectWrapper messageDataType
+)
+
+var (
+ _ pref.Message = (*messageReflectWrapper)(nil)
+ _ pvalue.Unwrapper = (*messageReflectWrapper)(nil)
+ _ pref.ProtoMessage = (*messageIfaceWrapper)(nil)
+ _ pvalue.Unwrapper = (*messageIfaceWrapper)(nil)
+)
+
+// MessageOf returns a reflective view over a message. The input must be a
+// pointer to a named Go struct. If the provided type has a ProtoReflect method,
+// it must be implemented by calling this method.
+func (mi *MessageInfo) MessageOf(m interface{}) pref.Message {
+ // TODO: Switch the input to be an opaque Pointer.
+ if reflect.TypeOf(m) != mi.GoType {
+ panic(fmt.Sprintf("type mismatch: got %T, want %v", m, mi.GoType))
+ }
+ p := pointerOfIface(m)
+ if p.IsNil() {
+ return mi.nilMessage.Init(mi)
+ }
+ return &messageReflectWrapper{p, mi}
+}
+
+func (m *messageReflectWrapper) pointer() pointer { return m.p }
+
+func (m *messageIfaceWrapper) ProtoReflect() pref.Message {
+ return (*messageReflectWrapper)(m)
+}
+func (m *messageIfaceWrapper) XXX_Methods() *piface.Methods {
+ // TODO: Consider not recreating this on every call.
+ m.mi.init()
+ return &piface.Methods{
+ Flags: piface.MethodFlagDeterministicMarshal,
+ MarshalAppend: m.marshalAppend,
+ Unmarshal: m.unmarshal,
+ Size: m.size,
+ IsInitialized: m.isInitialized,
+ }
+}
+func (m *messageIfaceWrapper) ProtoUnwrap() interface{} {
+ return m.p.AsIfaceOf(m.mi.GoType.Elem())
+}
+func (m *messageIfaceWrapper) marshalAppend(b []byte, _ pref.ProtoMessage, opts piface.MarshalOptions) ([]byte, error) {
+ return m.mi.marshalAppendPointer(b, m.p, newMarshalOptions(opts))
+}
+func (m *messageIfaceWrapper) unmarshal(b []byte, _ pref.ProtoMessage, opts piface.UnmarshalOptions) error {
+ _, err := m.mi.unmarshalPointer(b, m.p, 0, newUnmarshalOptions(opts))
+ return err
+}
+func (m *messageIfaceWrapper) size(msg pref.ProtoMessage) (size int) {
+ return m.mi.sizePointer(m.p, 0)
+}
+func (m *messageIfaceWrapper) isInitialized(_ pref.ProtoMessage) error {
+ return m.mi.isInitializedPointer(m.p)
+}
+
+type extensionMap map[int32]ExtensionField
+
+func (m *extensionMap) Range(f func(pref.FieldDescriptor, pref.Value) bool) {
+ if m != nil {
+ for _, x := range *m {
+ xt := x.GetType()
+ if !f(xt, xt.ValueOf(x.GetValue())) {
+ return
+ }
+ }
+ }
+}
+func (m *extensionMap) Has(xt pref.ExtensionType) (ok bool) {
+ if m != nil {
+ _, ok = (*m)[int32(xt.Number())]
+ }
+ return ok
+}
+func (m *extensionMap) Clear(xt pref.ExtensionType) {
+ delete(*m, int32(xt.Number()))
+}
+func (m *extensionMap) Get(xt pref.ExtensionType) pref.Value {
+ if m != nil {
+ if x, ok := (*m)[int32(xt.Number())]; ok {
+ return xt.ValueOf(x.GetValue())
+ }
+ }
+ if !isComposite(xt) {
+ return defaultValueOf(xt)
+ }
+ return frozenValueOf(xt.New())
+}
+func (m *extensionMap) Set(xt pref.ExtensionType, v pref.Value) {
+ if *m == nil {
+ *m = make(map[int32]ExtensionField)
+ }
+ var x ExtensionField
+ x.SetType(xt)
+ x.SetEagerValue(xt.InterfaceOf(v))
+ (*m)[int32(xt.Number())] = x
+}
+func (m *extensionMap) Mutable(xt pref.ExtensionType) pref.Value {
+ if !isComposite(xt) {
+ panic("invalid Mutable on field with non-composite type")
+ }
+ if x, ok := (*m)[int32(xt.Number())]; ok {
+ return xt.ValueOf(x.GetValue())
+ }
+ v := xt.New()
+ m.Set(xt, v)
+ return v
+}
+
+func isComposite(fd pref.FieldDescriptor) bool {
+ return fd.Kind() == pref.MessageKind || fd.Kind() == pref.GroupKind || fd.IsList() || fd.IsMap()
+}
+
+// checkField verifies that the provided field descriptor is valid.
+// Exactly one of the returned values is populated.
+func (mi *MessageInfo) checkField(fd pref.FieldDescriptor) (*fieldInfo, pref.ExtensionType) {
+ if fi := mi.fields[fd.Number()]; fi != nil {
+ if fi.fieldDesc != fd {
+ panic("mismatching field descriptor")
+ }
+ return fi, nil
+ }
+ if fd.IsExtension() {
+ if fd.ContainingMessage().FullName() != mi.PBType.FullName() {
+ // TODO: Should this be exact containing message descriptor match?
+ panic("mismatching containing message")
+ }
+ if !mi.PBType.ExtensionRanges().Has(fd.Number()) {
+ panic("invalid extension field")
+ }
+ return nil, fd.(pref.ExtensionType)
+ }
+ panic("invalid field descriptor")
+}