1 // Protocol Buffers - Google's data interchange format
2 // Copyright 2008 Google Inc. All rights reserved.
3 // http://code.google.com/p/protobuf/
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6 // modification, are permitted provided that the following conditions are
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13 // in the documentation and/or other materials provided with the
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17 // this software without specific prior written permission.
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31 // Author: kenton@google.com (Kenton Varda)
32 // Based on original Protocol Buffers design by
33 // Sanjay Ghemawat, Jeff Dean, and others.
35 // Defines an implementation of Message which can emulate types which are not
36 // known at compile-time.
38 #ifndef GOOGLE_PROTOBUF_DYNAMIC_MESSAGE_H__
39 #define GOOGLE_PROTOBUF_DYNAMIC_MESSAGE_H__
41 #include <google/protobuf/message.h>
42 #include <google/protobuf/stubs/common.h>
47 // Defined in other files.
48 class Descriptor; // descriptor.h
49 class DescriptorPool; // descriptor.h
51 // Constructs implementations of Message which can emulate types which are not
52 // known at compile-time.
54 // Sometimes you want to be able to manipulate protocol types that you don't
55 // know about at compile time. It would be nice to be able to construct
56 // a Message object which implements the message type given by any arbitrary
57 // Descriptor. DynamicMessage provides this.
59 // As it turns out, a DynamicMessage needs to construct extra
60 // information about its type in order to operate. Most of this information
61 // can be shared between all DynamicMessages of the same type. But, caching
62 // this information in some sort of global map would be a bad idea, since
63 // the cached information for a particular descriptor could outlive the
64 // descriptor itself. To avoid this problem, DynamicMessageFactory
65 // encapsulates this "cache". All DynamicMessages of the same type created
66 // from the same factory will share the same support data. Any Descriptors
67 // used with a particular factory must outlive the factory.
68 class LIBPROTOBUF_EXPORT DynamicMessageFactory : public MessageFactory {
70 // Construct a DynamicMessageFactory that will search for extensions in
71 // the DescriptorPool in which the extendee is defined.
72 DynamicMessageFactory();
74 // Construct a DynamicMessageFactory that will search for extensions in
75 // the given DescriptorPool.
77 // DEPRECATED: Use CodedInputStream::SetExtensionRegistry() to tell the
78 // parser to look for extensions in an alternate pool. However, note that
79 // this is almost never what you want to do. Almost all users should use
80 // the zero-arg constructor.
81 DynamicMessageFactory(const DescriptorPool* pool);
83 ~DynamicMessageFactory();
85 // Call this to tell the DynamicMessageFactory that if it is given a
86 // Descriptor d for which:
87 // d->file()->pool() == DescriptorPool::generated_pool(),
88 // then it should delegate to MessageFactory::generated_factory() instead
89 // of constructing a dynamic implementation of the message. In theory there
90 // is no down side to doing this, so it may become the default in the future.
91 void SetDelegateToGeneratedFactory(bool enable) {
92 delegate_to_generated_factory_ = enable;
95 // implements MessageFactory ---------------------------------------
97 // Given a Descriptor, constructs the default (prototype) Message of that
98 // type. You can then call that message's New() method to construct a
99 // mutable message of that type.
101 // Calling this method twice with the same Descriptor returns the same
102 // object. The returned object remains property of the factory and will
103 // be destroyed when the factory is destroyed. Also, any objects created
104 // by calling the prototype's New() method share some data with the
105 // prototype, so these must be destroyed before the DynamicMessageFactory
108 // The given descriptor must outlive the returned message, and hence must
109 // outlive the DynamicMessageFactory.
111 // The method is thread-safe.
112 const Message* GetPrototype(const Descriptor* type);
115 const DescriptorPool* pool_;
116 bool delegate_to_generated_factory_;
118 // This struct just contains a hash_map. We can't #include <google/protobuf/stubs/hash.h> from
119 // this header due to hacks needed for hash_map portability in the open source
120 // release. Namely, stubs/hash.h, which defines hash_map portably, is not a
121 // public header (for good reason), but dynamic_message.h is, and public
122 // headers may only #include other public headers.
124 scoped_ptr<PrototypeMap> prototypes_;
125 mutable Mutex prototypes_mutex_;
127 friend class DynamicMessage;
128 const Message* GetPrototypeNoLock(const Descriptor* type);
130 GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(DynamicMessageFactory);
133 } // namespace protobuf
135 } // namespace google
136 #endif // GOOGLE_PROTOBUF_DYNAMIC_MESSAGE_H__