/usr/include/mongo/util/shared_buffer.h is in libmongoclient-dev 1.1.2-6ubuntu3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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 | /**
* Copyright (C) 2014 MongoDB Inc.
*
* 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.
*/
#pragma once
#include <boost/intrusive_ptr.hpp>
#include "mongo/platform/atomic_word.h"
namespace mongo {
class SharedBuffer {
public:
SharedBuffer() {}
void swap(SharedBuffer& other) {
_holder.swap(other._holder);
}
/**
* C++03 compatible way of writing std::move(someSharedBuffer)
*/
SharedBuffer moveFrom() {
SharedBuffer out;
this->swap(out);
return out;
}
static SharedBuffer allocate(size_t bytes) {
return takeOwnership(static_cast<char*>(malloc(sizeof(Holder) + bytes)));
}
/**
* Given a pointer to a region of un-owned data, prefixed by sufficient space for a
* SharedBuffer::Holder object, return an SharedBuffer that owns the
* memory.
*
* This class will call free(holderPrefixedData), so it must have been allocated in a way
* that makes that valid.
*/
static SharedBuffer takeOwnership(char* holderPrefixedData) {
// Initialize the refcount to 1 so we don't need to increment it in the constructor
// (see private Holder* constructor below).
//
// TODO: Should dassert alignment of holderPrefixedData
// here if possible.
return SharedBuffer(new (holderPrefixedData) Holder(1U));
}
char* get() const {
return _holder ? _holder->data() : NULL;
}
class Holder {
public:
explicit Holder(AtomicUInt32::WordType initial = AtomicUInt32::WordType())
: _refCount(initial) {}
// these are called automatically by boost::intrusive_ptr
friend void intrusive_ptr_add_ref(Holder* h) {
h->_refCount.fetchAndAdd(1);
}
friend void intrusive_ptr_release(Holder* h) {
if (h->_refCount.subtractAndFetch(1) == 0) {
// We placement new'ed a Holder in takeOwnership above,
// so we must destroy the object here.
h->~Holder();
free(h);
}
}
char* data() {
return reinterpret_cast<char*>(this + 1);
}
const char* data() const {
return reinterpret_cast<const char*>(this + 1);
}
private:
AtomicUInt32 _refCount;
};
private:
explicit SharedBuffer(Holder* holder) : _holder(holder, /*add_ref=*/false) {
// NOTE: The 'false' above is because we have already initialized the Holder with a
// refcount of '1' in takeOwnership above. This avoids an atomic increment.
}
boost::intrusive_ptr<Holder> _holder;
};
inline void swap(SharedBuffer& one, SharedBuffer& two) {
one.swap(two);
}
}
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