98 lines
3.8 KiB
C++
98 lines
3.8 KiB
C++
// 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.
|
|
|
|
#ifndef GOOGLE_PROTOBUF_EXPLICITLY_CONSTRUCTED_H__
|
|
#define GOOGLE_PROTOBUF_EXPLICITLY_CONSTRUCTED_H__
|
|
|
|
#include <stdint.h>
|
|
|
|
#include <utility>
|
|
|
|
#include <google/protobuf/stubs/logging.h>
|
|
#include <google/protobuf/stubs/common.h>
|
|
|
|
// clang-format off
|
|
#include <google/protobuf/port_def.inc>
|
|
// clang-format on
|
|
|
|
namespace google {
|
|
namespace protobuf {
|
|
namespace internal {
|
|
|
|
// Wraps a variable whose constructor and destructor are explicitly
|
|
// called. It is particularly useful for a global variable, without its
|
|
// constructor and destructor run on start and end of the program lifetime.
|
|
// This circumvents the initial construction order fiasco, while keeping
|
|
// the address of the empty string a compile time constant.
|
|
//
|
|
// Pay special attention to the initialization state of the object.
|
|
// 1. The object is "uninitialized" to begin with.
|
|
// 2. Call Construct() or DefaultConstruct() only if the object is
|
|
// uninitialized. After the call, the object becomes "initialized".
|
|
// 3. Call get() and get_mutable() only if the object is initialized.
|
|
// 4. Call Destruct() only if the object is initialized.
|
|
// After the call, the object becomes uninitialized.
|
|
template <typename T, size_t min_align = 1>
|
|
class ExplicitlyConstructed {
|
|
public:
|
|
void DefaultConstruct() { new (&union_) T(); }
|
|
|
|
template <typename... Args>
|
|
void Construct(Args&&... args) {
|
|
new (&union_) T(std::forward<Args>(args)...);
|
|
}
|
|
|
|
void Destruct() { get_mutable()->~T(); }
|
|
|
|
constexpr const T& get() const { return reinterpret_cast<const T&>(union_); }
|
|
T* get_mutable() { return reinterpret_cast<T*>(&union_); }
|
|
|
|
private:
|
|
union AlignedUnion {
|
|
alignas(min_align > alignof(T) ? min_align
|
|
: alignof(T)) char space[sizeof(T)];
|
|
int64_t align_to_int64;
|
|
void* align_to_ptr;
|
|
} union_;
|
|
};
|
|
|
|
// ArenaStringPtr compatible explicitly constructed string type.
|
|
// This empty string type is aligned with a minimum alignment of 8 bytes
|
|
// which is the minimum requirement of ArenaStringPtr
|
|
using ExplicitlyConstructedArenaString = ExplicitlyConstructed<std::string, 8>;
|
|
|
|
} // namespace internal
|
|
} // namespace protobuf
|
|
} // namespace google
|
|
|
|
#include <google/protobuf/port_undef.inc>
|
|
|
|
#endif // GOOGLE_PROTOBUF_EXPLICITLY_CONSTRUCTED_H__
|