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// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.
// http://code.google.com/p/protobuf/
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Author: kenton@google.com (Kenton Varda)
// Based on original Protocol Buffers design by
// Sanjay Ghemawat, Jeff Dean, and others.
//
// Defines an implementation of Message which can emulate types which are not
// known at compile-time.
#ifndef GOOGLE_PROTOBUF_DYNAMIC_MESSAGE_H__
#define GOOGLE_PROTOBUF_DYNAMIC_MESSAGE_H__
#include <google/protobuf/message.h>
#include <google/protobuf/stubs/common.h>
namespace google {
namespace protobuf {
// Defined in other files.
class Descriptor; // descriptor.h
class DescriptorPool; // descriptor.h
// Constructs implementations of Message which can emulate types which are not
// known at compile-time.
//
// Sometimes you want to be able to manipulate protocol types that you don't
// know about at compile time. It would be nice to be able to construct
// a Message object which implements the message type given by any arbitrary
// Descriptor. DynamicMessage provides this.
//
// As it turns out, a DynamicMessage needs to construct extra
// information about its type in order to operate. Most of this information
// can be shared between all DynamicMessages of the same type. But, caching
// this information in some sort of global map would be a bad idea, since
// the cached information for a particular descriptor could outlive the
// descriptor itself. To avoid this problem, DynamicMessageFactory
// encapsulates this "cache". All DynamicMessages of the same type created
// from the same factory will share the same support data. Any Descriptors
// used with a particular factory must outlive the factory.
class LIBPROTOBUF_EXPORT DynamicMessageFactory : public MessageFactory {
public:
// Construct a DynamicMessageFactory that will search for extensions in
// the DescriptorPool in which the exendee is defined.
DynamicMessageFactory();
// Construct a DynamicMessageFactory that will search for extensions in
// the given DescriptorPool.
DynamicMessageFactory(const DescriptorPool* pool);
~DynamicMessageFactory();
// implements MessageFactory ---------------------------------------
// Given a Descriptor, constructs the default (prototype) Message of that
// type. You can then call that message's New() method to construct a
// mutable message of that type.
//
// Calling this method twice with the same Descriptor returns the same
// object. The returned object remains property of the factory and will
// be destroyed when the factory is destroyed. Also, any objects created
// by calling the prototype's New() method share some data with the
// prototype, so these must be destoyed before the DynamicMessageFactory
// is destroyed.
//
// The given descriptor must outlive the returned message, and hence must
// outlive the DynamicMessageFactory.
//
// Note that while GetPrototype() is idempotent, it is not const. This
// implies that it is not thread-safe to call GetPrototype() on the same
// DynamicMessageFactory in two different threads simultaneously. However,
// the returned objects are just as thread-safe as any other Message.
const Message* GetPrototype(const Descriptor* type);
private:
const DescriptorPool* pool_;
// This struct just contains a hash_map. We can't #include <google/protobuf/stubs/hash.h> from
// this header due to hacks needed for hash_map portability in the open source
// release. Namely, stubs/hash.h, which defines hash_map portably, is not a
// public header (for good reason), but dynamic_message.h is, and public
// headers may only #include other public headers.
struct PrototypeMap;
scoped_ptr<PrototypeMap> prototypes_;
GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(DynamicMessageFactory);
};
} // namespace protobuf
} // namespace google
#endif // GOOGLE_PROTOBUF_DYNAMIC_MESSAGE_H__
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