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      1 // Protocol Buffers - Google's data interchange format
      2 // Copyright 2008 Google Inc.  All rights reserved.
      3 // http://code.google.com/p/protobuf/
      4 //
      5 // Redistribution and use in source and binary forms, with or without
      6 // modification, are permitted provided that the following conditions are
      7 // met:
      8 //
      9 //     * Redistributions of source code must retain the above copyright
     10 // notice, this list of conditions and the following disclaimer.
     11 //     * Redistributions in binary form must reproduce the above
     12 // copyright notice, this list of conditions and the following disclaimer
     13 // in the documentation and/or other materials provided with the
     14 // distribution.
     15 //     * Neither the name of Google Inc. nor the names of its
     16 // contributors may be used to endorse or promote products derived from
     17 // this software without specific prior written permission.
     18 //
     19 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
     20 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
     21 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
     22 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
     23 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
     24 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
     25 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     26 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     27 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     28 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
     29 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     30 
     31 // Author: kenton (at) google.com (Kenton Varda)
     32 //  Based on original Protocol Buffers design by
     33 //  Sanjay Ghemawat, Jeff Dean, and others.
     34 //
     35 // Defines an implementation of Message which can emulate types which are not
     36 // known at compile-time.
     37 
     38 #ifndef GOOGLE_PROTOBUF_DYNAMIC_MESSAGE_H__
     39 #define GOOGLE_PROTOBUF_DYNAMIC_MESSAGE_H__
     40 
     41 #include <google/protobuf/message.h>
     42 #include <google/protobuf/stubs/common.h>
     43 
     44 namespace google {
     45 namespace protobuf {
     46 
     47 // Defined in other files.
     48 class Descriptor;        // descriptor.h
     49 class DescriptorPool;    // descriptor.h
     50 
     51 // Constructs implementations of Message which can emulate types which are not
     52 // known at compile-time.
     53 //
     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.
     58 //
     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 {
     69  public:
     70   // Construct a DynamicMessageFactory that will search for extensions in
     71   // the DescriptorPool in which the extendee is defined.
     72   DynamicMessageFactory();
     73 
     74   // Construct a DynamicMessageFactory that will search for extensions in
     75   // the given DescriptorPool.
     76   //
     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);
     82 
     83   ~DynamicMessageFactory();
     84 
     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;
     93   }
     94 
     95   // implements MessageFactory ---------------------------------------
     96 
     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.
    100   //
    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
    106   // is destroyed.
    107   //
    108   // The given descriptor must outlive the returned message, and hence must
    109   // outlive the DynamicMessageFactory.
    110   //
    111   // The method is thread-safe.
    112   const Message* GetPrototype(const Descriptor* type);
    113 
    114  private:
    115   const DescriptorPool* pool_;
    116   bool delegate_to_generated_factory_;
    117 
    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.
    123   struct PrototypeMap;
    124   scoped_ptr<PrototypeMap> prototypes_;
    125   mutable Mutex prototypes_mutex_;
    126 
    127   friend class DynamicMessage;
    128   const Message* GetPrototypeNoLock(const Descriptor* type);
    129 
    130   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(DynamicMessageFactory);
    131 };
    132 
    133 }  // namespace protobuf
    134 
    135 }  // namespace google
    136 #endif  // GOOGLE_PROTOBUF_DYNAMIC_MESSAGE_H__
    137