aboutsummaryrefslogtreecommitdiffhomepage
path: root/src/google/protobuf/metadata.h
blob: fdee150b44f5c7d92ba1ccf0fc062c4887e65b8c (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// https://developers.google.com/protocol-buffers/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// This header file defines an internal class that encapsulates internal message
// metadata (Unknown-field set, Arena pointer, ...) and allows its
// representation to be made more space-efficient via various optimizations.
//
// Note that this is distinct from google::protobuf::Metadata, which encapsulates
// Descriptor and Reflection pointers.

#ifndef GOOGLE_PROTOBUF_METADATA_H__
#define GOOGLE_PROTOBUF_METADATA_H__

#include <google/protobuf/stubs/common.h>
#include <google/protobuf/arena.h>
#include <google/protobuf/unknown_field_set.h>

namespace google {
namespace protobuf {
namespace internal {

// This is the representation for messages that support arena allocation. It
// uses a tagged pointer to either store the Arena pointer, if there are no
// unknown fields, or a pointer to a block of memory with both the Arena pointer
// and the UnknownFieldSet, if there are unknown fields. This optimization
// allows for "zero-overhead" storage of the Arena pointer, relative to the
// above baseline implementation.
//
// The tagged pointer uses the LSB to disambiguate cases, and uses bit 0 == 0 to
// indicate an arena pointer and bit 0 == 1 to indicate a UFS+Arena-container
// pointer.
class LIBPROTOBUF_EXPORT InternalMetadataWithArena {
 public:
  InternalMetadataWithArena() : ptr_(NULL) {}
  explicit InternalMetadataWithArena(Arena* arena)
      : ptr_ (arena) {}

  ~InternalMetadataWithArena() {
    if (have_unknown_fields() && arena() == NULL) {
      delete PtrValue<Container>();
    }
    ptr_ = NULL;
  }

  GOOGLE_ATTRIBUTE_ALWAYS_INLINE const UnknownFieldSet& unknown_fields() const {
    if (GOOGLE_PREDICT_FALSE(have_unknown_fields())) {
      return PtrValue<Container>()->unknown_fields_;
    } else {
      return *UnknownFieldSet::default_instance();
    }
  }

  GOOGLE_ATTRIBUTE_ALWAYS_INLINE UnknownFieldSet* mutable_unknown_fields() {
    if (GOOGLE_PREDICT_TRUE(have_unknown_fields())) {
      return &PtrValue<Container>()->unknown_fields_;
    } else {
      return mutable_unknown_fields_slow();
    }
  }

  GOOGLE_ATTRIBUTE_ALWAYS_INLINE Arena* arena() const {
    if (GOOGLE_PREDICT_FALSE(have_unknown_fields())) {
      return PtrValue<Container>()->arena_;
    } else {
      return PtrValue<Arena>();
    }
  }

  GOOGLE_ATTRIBUTE_ALWAYS_INLINE bool have_unknown_fields() const {
    return PtrTag() == kTagContainer;
  }

  GOOGLE_ATTRIBUTE_ALWAYS_INLINE void Swap(InternalMetadataWithArena* other) {
    // Semantics here are that we swap only the unknown fields, not the arena
    // pointer. We cannot simply swap ptr_ with other->ptr_ because we need to
    // maintain our own arena ptr. Also, our ptr_ and other's ptr_ may be in
    // different states (direct arena pointer vs. container with UFS) so we
    // cannot simply swap ptr_ and then restore the arena pointers. We reuse
    // UFS's swap implementation instead.
    if (have_unknown_fields() || other->have_unknown_fields()) {
      mutable_unknown_fields()->Swap(other->mutable_unknown_fields());
    }
  }

  GOOGLE_ATTRIBUTE_ALWAYS_INLINE void* raw_arena_ptr() const {
    return ptr_;
  }

 private:
  void* ptr_;

  // Tagged pointer implementation.
  enum {
    // ptr_ is an Arena*.
    kTagArena = 0,
    // ptr_ is a Container*.
    kTagContainer = 1,
  };
  static const intptr_t kPtrTagMask = 1;
  static const intptr_t kPtrValueMask = ~kPtrTagMask;

  // Accessors for pointer tag and pointer value.
  GOOGLE_ATTRIBUTE_ALWAYS_INLINE int PtrTag() const {
    return reinterpret_cast<intptr_t>(ptr_) & kPtrTagMask;
  }

  template<typename T> T* PtrValue() const {
    return reinterpret_cast<T*>(
        reinterpret_cast<intptr_t>(ptr_) & kPtrValueMask);
  }

  // If ptr_'s tag is kTagContainer, it points to an instance of this struct.
  struct Container {
    UnknownFieldSet unknown_fields_;
    Arena* arena_;
  };

  GOOGLE_ATTRIBUTE_NOINLINE UnknownFieldSet* mutable_unknown_fields_slow() {
    Arena* my_arena = arena();
    Container* container = Arena::Create<Container>(my_arena);
    ptr_ = reinterpret_cast<void*>(
        reinterpret_cast<intptr_t>(container) | kTagContainer);
    container->arena_ = my_arena;
    return &(container->unknown_fields_);
  }
};

// Temporary compatibility typedef. Remove once this is released in components
// and upb CL is submitted.
typedef InternalMetadataWithArena InternalMetadata;

}  // namespace internal
}  // namespace protobuf

}  // namespace google
#endif  // GOOGLE_PROTOBUF_METADATA_H__