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// Protocol Buffers - Google's data interchange format |
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// Copyright 2008 Google Inc. |
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// http://code.google.com/p/protobuf/ |
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// |
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// Licensed under the Apache License, Version 2.0 (the "License"); |
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// you may not use this file except in compliance with the License. |
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// You may obtain a copy of the License at |
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// |
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// http://www.apache.org/licenses/LICENSE-2.0 |
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// |
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// Unless required by applicable law or agreed to in writing, software |
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// distributed under the License is distributed on an "AS IS" BASIS, |
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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// See the License for the specific language governing permissions and |
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// limitations under the License. |
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|
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// Author: kenton@google.com (Kenton Varda) |
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// Based on original Protocol Buffers design by |
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// Sanjay Ghemawat, Jeff Dean, and others. |
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// |
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// DynamicMessage is implemented by constructing a data structure which |
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// has roughly the same memory layout as a generated message would have. |
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// Then, we use GeneratedMessageReflection to implement our reflection |
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// interface. All the other operations we need to implement (e.g. |
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// parsing, copying, etc.) are already implemented in terms of |
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// Reflection, so the rest is easy. |
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// |
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// The up side of this strategy is that it's very efficient. We don't |
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// need to use hash_maps or generic representations of fields. The |
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// down side is that this is a low-level memory management hack which |
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// can be tricky to get right. |
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// |
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// As mentioned in the header, we only expose a DynamicMessageFactory |
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// publicly, not the DynamicMessage class itself. This is because |
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// GenericMessageReflection wants to have a pointer to a "default" |
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// copy of the class, with all fields initialized to their default |
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// values. We only want to construct one of these per message type, |
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// so DynamicMessageFactory stores a cache of default messages for |
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// each type it sees (each unique Descriptor pointer). The code |
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// refers to the "default" copy of the class as the "prototype". |
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// |
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// Note on memory allocation: This module often calls "operator new()" |
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// to allocate untyped memory, rather than calling something like |
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// "new uint8[]". This is because "operator new()" means "Give me some |
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// space which I can use as I please." while "new uint8[]" means "Give |
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// me an array of 8-bit integers.". In practice, the later may return |
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// a pointer that is not aligned correctly for general use. I believe |
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// Item 8 of "More Effective C++" discusses this in more detail, though |
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// I don't have the book on me right now so I'm not sure. |
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|
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#include <algorithm> |
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#include <google/protobuf/stubs/hash.h> |
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|
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#include <google/protobuf/stubs/common.h> |
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|
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#include <google/protobuf/dynamic_message.h> |
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#include <google/protobuf/descriptor.h> |
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#include <google/protobuf/descriptor.pb.h> |
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#include <google/protobuf/generated_message_reflection.h> |
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#include <google/protobuf/reflection_ops.h> |
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#include <google/protobuf/repeated_field.h> |
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#include <google/protobuf/extension_set.h> |
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#include <google/protobuf/wire_format.h> |
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|
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namespace google { |
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namespace protobuf { |
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|
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using internal::WireFormat; |
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using internal::ExtensionSet; |
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using internal::GeneratedMessageReflection; |
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using internal::GenericRepeatedField; |
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|
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|
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// =================================================================== |
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// Some helper tables and functions... |
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|
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namespace { |
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|
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// Compute the byte size of the in-memory representation of the field. |
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int FieldSpaceUsed(const FieldDescriptor* field) { |
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typedef FieldDescriptor FD; // avoid line wrapping |
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if (field->label() == FD::LABEL_REPEATED) { |
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switch (field->cpp_type()) { |
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case FD::CPPTYPE_INT32 : return sizeof(RepeatedField<int32 >); |
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case FD::CPPTYPE_INT64 : return sizeof(RepeatedField<int64 >); |
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case FD::CPPTYPE_UINT32 : return sizeof(RepeatedField<uint32 >); |
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case FD::CPPTYPE_UINT64 : return sizeof(RepeatedField<uint64 >); |
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case FD::CPPTYPE_DOUBLE : return sizeof(RepeatedField<double >); |
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case FD::CPPTYPE_FLOAT : return sizeof(RepeatedField<float >); |
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case FD::CPPTYPE_BOOL : return sizeof(RepeatedField<bool >); |
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case FD::CPPTYPE_ENUM : return sizeof(RepeatedField<int >); |
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case FD::CPPTYPE_MESSAGE: return sizeof(RepeatedPtrField<Message>); |
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|
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case FD::CPPTYPE_STRING: |
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return sizeof(RepeatedPtrField<string>); |
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break; |
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} |
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} else { |
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switch (field->cpp_type()) { |
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case FD::CPPTYPE_INT32 : return sizeof(int32 ); |
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case FD::CPPTYPE_INT64 : return sizeof(int64 ); |
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case FD::CPPTYPE_UINT32 : return sizeof(uint32 ); |
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case FD::CPPTYPE_UINT64 : return sizeof(uint64 ); |
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case FD::CPPTYPE_DOUBLE : return sizeof(double ); |
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case FD::CPPTYPE_FLOAT : return sizeof(float ); |
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case FD::CPPTYPE_BOOL : return sizeof(bool ); |
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case FD::CPPTYPE_ENUM : return sizeof(int ); |
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case FD::CPPTYPE_MESSAGE: return sizeof(Message*); |
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|
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case FD::CPPTYPE_STRING: |
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return sizeof(string*); |
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break; |
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} |
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} |
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|
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GOOGLE_LOG(DFATAL) << "Can't get here."; |
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return 0; |
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} |
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|
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struct DescendingFieldSizeOrder { |
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inline bool operator()(const FieldDescriptor* a, |
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const FieldDescriptor* b) { |
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// All repeated fields come first. |
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if (a->is_repeated()) { |
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if (b->is_repeated()) { |
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// Repeated fields and are not ordered with respect to each other. |
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return false; |
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} else { |
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return true; |
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} |
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} else if (b->is_repeated()) { |
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return false; |
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} else { |
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// Remaining fields in descending order by size. |
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return FieldSpaceUsed(a) > FieldSpaceUsed(b); |
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} |
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} |
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}; |
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|
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inline int DivideRoundingUp(int i, int j) { |
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return (i + (j - 1)) / j; |
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} |
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|
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static const int kSafeAlignment = sizeof(uint64); |
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|
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// Rounds the given byte offset up to the next offset aligned such that any |
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// type may be stored at it. |
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inline int AlignOffset(int offset) { |
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return DivideRoundingUp(offset, kSafeAlignment) * kSafeAlignment; |
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} |
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|
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#define bitsizeof(T) (sizeof(T) * 8) |
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|
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} // namespace |
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|
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// =================================================================== |
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|
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class DynamicMessage : public Message { |
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public: |
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struct TypeInfo { |
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int size; |
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int has_bits_offset; |
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int unknown_fields_offset; |
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int extensions_offset; |
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|
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// Not owned by the TypeInfo. |
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DynamicMessageFactory* factory; // The factory that created this object. |
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const DescriptorPool* pool; // The factory's DescriptorPool. |
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const Descriptor* type; // Type of this DynamicMessage. |
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|
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// Warning: The order in which the following pointers are defined is |
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// important (the prototype must be deleted *before* the offsets). |
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scoped_array<int> offsets; |
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scoped_ptr<const GeneratedMessageReflection> reflection; |
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scoped_ptr<const DynamicMessage> prototype; |
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}; |
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|
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DynamicMessage(const TypeInfo* type_info); |
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~DynamicMessage(); |
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|
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// Called on the prototype after construction to initialize message fields. |
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void CrossLinkPrototypes(); |
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|
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// implements Message ---------------------------------------------- |
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|
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Message* New() const; |
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|
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int GetCachedSize() const; |
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void SetCachedSize(int size) const; |
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|
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const Descriptor* GetDescriptor() const; |
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const Reflection* GetReflection() const; |
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|
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private: |
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GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(DynamicMessage); |
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|
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inline bool is_prototype() const { |
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return type_info_->prototype == this || |
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// If type_info_->prototype is NULL, then we must be constructing |
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// the prototype now, which means we must be the prototype. |
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type_info_->prototype == NULL; |
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} |
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|
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inline void* OffsetToPointer(int offset) { |
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return reinterpret_cast<uint8*>(this) + offset; |
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} |
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inline const void* OffsetToPointer(int offset) const { |
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return reinterpret_cast<const uint8*>(this) + offset; |
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} |
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|
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const TypeInfo* type_info_; |
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|
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// TODO(kenton): Make this an atomic<int> when C++ supports it. |
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mutable int cached_byte_size_; |
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}; |
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|
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DynamicMessage::DynamicMessage(const TypeInfo* type_info) |
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: type_info_(type_info), |
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cached_byte_size_(0) { |
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// We need to call constructors for various fields manually and set |
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// default values where appropriate. We use placement new to call |
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// constructors. If you haven't heard of placement new, I suggest Googling |
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// it now. We use placement new even for primitive types that don't have |
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// constructors for consistency. (In theory, placement new should be used |
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// any time you are trying to convert untyped memory to typed memory, though |
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// in practice that's not strictly necessary for types that don't have a |
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// constructor.) |
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|
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const Descriptor* descriptor = type_info_->type; |
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|
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new(OffsetToPointer(type_info_->unknown_fields_offset)) UnknownFieldSet; |
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|
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if (type_info_->extensions_offset != -1) { |
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new(OffsetToPointer(type_info_->extensions_offset)) |
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ExtensionSet(&type_info_->type, type_info_->pool, type_info_->factory); |
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} |
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|
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for (int i = 0; i < descriptor->field_count(); i++) { |
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const FieldDescriptor* field = descriptor->field(i); |
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void* field_ptr = OffsetToPointer(type_info_->offsets[i]); |
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switch (field->cpp_type()) { |
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#define HANDLE_TYPE(CPPTYPE, TYPE) \ |
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case FieldDescriptor::CPPTYPE_##CPPTYPE: \ |
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if (!field->is_repeated()) { \ |
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new(field_ptr) TYPE(field->default_value_##TYPE()); \ |
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} else { \ |
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new(field_ptr) RepeatedField<TYPE>(); \ |
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} \ |
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break; |
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|
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HANDLE_TYPE(INT32 , int32 ); |
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HANDLE_TYPE(INT64 , int64 ); |
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HANDLE_TYPE(UINT32, uint32); |
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HANDLE_TYPE(UINT64, uint64); |
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HANDLE_TYPE(DOUBLE, double); |
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HANDLE_TYPE(FLOAT , float ); |
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HANDLE_TYPE(BOOL , bool ); |
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#undef HANDLE_TYPE |
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|
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case FieldDescriptor::CPPTYPE_ENUM: |
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if (!field->is_repeated()) { |
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new(field_ptr) int(field->default_value_enum()->number()); |
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} else { |
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new(field_ptr) RepeatedField<int>(); |
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} |
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break; |
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|
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case FieldDescriptor::CPPTYPE_STRING: |
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if (!field->is_repeated()) { |
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if (is_prototype()) { |
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new(field_ptr) const string*(&field->default_value_string()); |
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} else { |
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string* default_value = |
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*reinterpret_cast<string* const*>( |
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type_info_->prototype->OffsetToPointer( |
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type_info_->offsets[i])); |
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new(field_ptr) string*(default_value); |
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} |
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} else { |
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new(field_ptr) RepeatedPtrField<string>(); |
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} |
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break; |
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|
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case FieldDescriptor::CPPTYPE_MESSAGE: { |
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// If this object is the prototype, its CPPTYPE_MESSAGE fields |
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// must be initialized later, in CrossLinkPrototypes(), so we don't |
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// initialize them here. |
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if (!is_prototype()) { |
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if (!field->is_repeated()) { |
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new(field_ptr) Message*(NULL); |
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} else { |
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const RepeatedPtrField<Message>* prototype_field = |
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reinterpret_cast<const RepeatedPtrField<Message>*>( |
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type_info_->prototype->OffsetToPointer( |
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type_info_->offsets[i])); |
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new(field_ptr) RepeatedPtrField<Message>( |
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prototype_field->prototype()); |
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} |
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} |
|
break; |
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} |
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} |
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} |
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} |
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|
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DynamicMessage::~DynamicMessage() { |
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const Descriptor* descriptor = type_info_->type; |
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|
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reinterpret_cast<UnknownFieldSet*>( |
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OffsetToPointer(type_info_->unknown_fields_offset))->~UnknownFieldSet(); |
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|
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if (type_info_->extensions_offset != -1) { |
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reinterpret_cast<ExtensionSet*>( |
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OffsetToPointer(type_info_->extensions_offset))->~ExtensionSet(); |
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} |
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|
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// We need to manually run the destructors for repeated fields and strings, |
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// just as we ran their constructors in the the DynamicMessage constructor. |
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// Additionally, if any singular embedded messages have been allocated, we |
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// need to delete them, UNLESS we are the prototype message of this type, |
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// in which case any embedded messages are other prototypes and shouldn't |
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// be touched. |
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for (int i = 0; i < descriptor->field_count(); i++) { |
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const FieldDescriptor* field = descriptor->field(i); |
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void* field_ptr = OffsetToPointer(type_info_->offsets[i]); |
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|
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if (field->is_repeated()) { |
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GenericRepeatedField* field = |
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reinterpret_cast<GenericRepeatedField*>(field_ptr); |
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field->~GenericRepeatedField(); |
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|
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} else if (field->cpp_type() == FieldDescriptor::CPPTYPE_STRING) { |
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string* ptr = *reinterpret_cast<string**>(field_ptr); |
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if (ptr != &field->default_value_string()) { |
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delete ptr; |
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} |
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} else if ((field->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE) && |
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!is_prototype()) { |
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Message* message = *reinterpret_cast<Message**>(field_ptr); |
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if (message != NULL) { |
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delete message; |
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} |
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} |
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} |
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} |
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|
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void DynamicMessage::CrossLinkPrototypes() { |
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// This should only be called on the prototype message. |
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GOOGLE_CHECK(is_prototype()); |
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|
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DynamicMessageFactory* factory = type_info_->factory; |
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const Descriptor* descriptor = type_info_->type; |
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|
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// Cross-link default messages. |
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for (int i = 0; i < descriptor->field_count(); i++) { |
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const FieldDescriptor* field = descriptor->field(i); |
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void* field_ptr = OffsetToPointer(type_info_->offsets[i]); |
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|
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if (field->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE) { |
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// For fields with message types, we need to cross-link with the |
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// prototype for the field's type. |
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const Message* field_prototype = |
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factory->GetPrototype(field->message_type()); |
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|
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if (field->is_repeated()) { |
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// For repeated fields, we actually construct the RepeatedPtrField |
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// here, but only for fields with message types. All other repeated |
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// fields are constructed in DynamicMessage's constructor. |
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new(field_ptr) RepeatedPtrField<Message>(field_prototype); |
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} else { |
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// For singular fields, the field is just a pointer which should |
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// point to the prototype. (OK to const_cast here because the |
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// prototype itself will only be available const to the outside |
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// world.) |
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new(field_ptr) Message*(const_cast<Message*>(field_prototype)); |
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} |
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} |
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} |
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} |
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|
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Message* DynamicMessage::New() const { |
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void* new_base = reinterpret_cast<uint8*>(operator new(type_info_->size)); |
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memset(new_base, 0, type_info_->size); |
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return new(new_base) DynamicMessage(type_info_); |
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} |
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|
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int DynamicMessage::GetCachedSize() const { |
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return cached_byte_size_; |
| 389 |
} |
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|
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void DynamicMessage::SetCachedSize(int size) const { |
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// This is theoretically not thread-compatible, but in practice it works |
| 393 |
// because if multiple threads write this simultaneously, they will be |
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// writing the exact same value. |
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cached_byte_size_ = size; |
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} |
| 397 |
|
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const Descriptor* DynamicMessage::GetDescriptor() const { |
| 399 |
return type_info_->type; |
| 400 |
} |
| 401 |
|
| 402 |
const Reflection* DynamicMessage::GetReflection() const { |
| 403 |
return type_info_->reflection.get(); |
| 404 |
} |
| 405 |
|
| 406 |
// =================================================================== |
| 407 |
|
| 408 |
struct DynamicMessageFactory::PrototypeMap { |
| 409 |
typedef hash_map<const Descriptor*, const DynamicMessage::TypeInfo*> Map; |
| 410 |
Map map_; |
| 411 |
}; |
| 412 |
|
| 413 |
DynamicMessageFactory::DynamicMessageFactory() |
| 414 |
: pool_(NULL), prototypes_(new PrototypeMap) { |
| 415 |
} |
| 416 |
|
| 417 |
DynamicMessageFactory::DynamicMessageFactory(const DescriptorPool* pool) |
| 418 |
: pool_(pool), prototypes_(new PrototypeMap) { |
| 419 |
} |
| 420 |
|
| 421 |
DynamicMessageFactory::~DynamicMessageFactory() { |
| 422 |
for (PrototypeMap::Map::iterator iter = prototypes_->map_.begin(); |
| 423 |
iter != prototypes_->map_.end(); ++iter) { |
| 424 |
delete iter->second; |
| 425 |
} |
| 426 |
} |
| 427 |
|
| 428 |
|
| 429 |
const Message* DynamicMessageFactory::GetPrototype(const Descriptor* type) { |
| 430 |
const DynamicMessage::TypeInfo** target = &prototypes_->map_[type]; |
| 431 |
if (*target != NULL) { |
| 432 |
// Already exists. |
| 433 |
return (*target)->prototype.get(); |
| 434 |
} |
| 435 |
|
| 436 |
DynamicMessage::TypeInfo* type_info = new DynamicMessage::TypeInfo; |
| 437 |
*target = type_info; |
| 438 |
|
| 439 |
type_info->type = type; |
| 440 |
type_info->pool = (pool_ == NULL) ? type->file()->pool() : pool_; |
| 441 |
type_info->factory = this; |
| 442 |
|
| 443 |
// We need to construct all the structures passed to |
| 444 |
// GeneratedMessageReflection's constructor. This includes: |
| 445 |
// - A block of memory that contains space for all the message's fields. |
| 446 |
// - An array of integers indicating the byte offset of each field within |
| 447 |
// this block. |
| 448 |
// - A big bitfield containing a bit for each field indicating whether |
| 449 |
// or not that field is set. |
| 450 |
|
| 451 |
// Compute size and offsets. |
| 452 |
int* offsets = new int[type->field_count()]; |
| 453 |
type_info->offsets.reset(offsets); |
| 454 |
|
| 455 |
// Sort the fields of this message in descending order by size. We |
| 456 |
// assume that if we then pack the fields tightly in this order, all fields |
| 457 |
// will end up properly-aligned, since all field sizes are powers of two or |
| 458 |
// are multiples of the system word size. |
| 459 |
scoped_array<const FieldDescriptor*> ordered_fields( |
| 460 |
new const FieldDescriptor*[type->field_count()]); |
| 461 |
for (int i = 0; i < type->field_count(); i++) { |
| 462 |
ordered_fields[i] = type->field(i); |
| 463 |
} |
| 464 |
stable_sort(&ordered_fields[0], &ordered_fields[type->field_count()], |
| 465 |
DescendingFieldSizeOrder()); |
| 466 |
|
| 467 |
// Decide all field offsets by packing in order. |
| 468 |
// We place the DynamicMessage object itself at the beginning of the allocated |
| 469 |
// space. |
| 470 |
int size = sizeof(DynamicMessage); |
| 471 |
size = AlignOffset(size); |
| 472 |
|
| 473 |
// Next the has_bits, which is an array of uint32s. |
| 474 |
type_info->has_bits_offset = size; |
| 475 |
int has_bits_array_size = |
| 476 |
DivideRoundingUp(type->field_count(), bitsizeof(uint32)); |
| 477 |
size += has_bits_array_size * sizeof(uint32); |
| 478 |
size = AlignOffset(size); |
| 479 |
|
| 480 |
// The ExtensionSet, if any. |
| 481 |
if (type->extension_range_count() > 0) { |
| 482 |
type_info->extensions_offset = size; |
| 483 |
size += sizeof(ExtensionSet); |
| 484 |
size = AlignOffset(size); |
| 485 |
} else { |
| 486 |
// No extensions. |
| 487 |
type_info->extensions_offset = -1; |
| 488 |
} |
| 489 |
|
| 490 |
// All the fields. We don't need to align after each field because they are |
| 491 |
// sorted in descending size order, and the size of a type is always a |
| 492 |
// multiple of its alignment. |
| 493 |
for (int i = 0; i < type->field_count(); i++) { |
| 494 |
offsets[ordered_fields[i]->index()] = size; |
| 495 |
size += FieldSpaceUsed(ordered_fields[i]); |
| 496 |
} |
| 497 |
|
| 498 |
// Add the UnknownFieldSet to the end. |
| 499 |
size = AlignOffset(size); |
| 500 |
type_info->unknown_fields_offset = size; |
| 501 |
size += sizeof(UnknownFieldSet); |
| 502 |
|
| 503 |
// Align the final size to make sure no clever allocators think that |
| 504 |
// alignment is not necessary. |
| 505 |
size = AlignOffset(size); |
| 506 |
type_info->size = size; |
| 507 |
|
| 508 |
// Allocate the prototype. |
| 509 |
void* base = operator new(size); |
| 510 |
memset(base, 0, size); |
| 511 |
DynamicMessage* prototype = new(base) DynamicMessage(type_info); |
| 512 |
type_info->prototype.reset(prototype); |
| 513 |
|
| 514 |
// Construct the reflection object. |
| 515 |
type_info->reflection.reset( |
| 516 |
new GeneratedMessageReflection( |
| 517 |
type_info->type, |
| 518 |
type_info->prototype.get(), |
| 519 |
type_info->offsets.get(), |
| 520 |
type_info->has_bits_offset, |
| 521 |
type_info->unknown_fields_offset, |
| 522 |
type_info->extensions_offset, |
| 523 |
type_info->pool)); |
| 524 |
|
| 525 |
// Cross link prototypes. |
| 526 |
prototype->CrossLinkPrototypes(); |
| 527 |
|
| 528 |
return prototype; |
| 529 |
} |
| 530 |
|
| 531 |
} // namespace protobuf |
| 532 |
} // namespace google |
| |