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/*
* Copyright (C) 2013-2018 Max Kellermann <max.kellermann@gmail.com>
*
* 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.
*
* 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
* FOUNDATION 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 SPARSE_BUFFER_HXX
#define SPARSE_BUFFER_HXX
#include "HugeAllocator.hxx"
#include "ConstBuffer.hxx"
#include "WritableBuffer.hxx"
#include <map>
#include <assert.h>
/**
* Helper class for #SparseBuffer which describes which portions of
* the buffer have "known" data.
*/
class SparseMap {
using size_type = std::size_t;
/**
* Key is start offset, value is end offset.
*/
using Map = std::map<size_type, size_type>;
using Iterator = typename Map::iterator;
Map map;
public:
explicit SparseMap(size_type size) noexcept
:map{{size, size}} {
assert(size > 0);
}
size_type size() const noexcept {
return GetEndOffset();
}
struct CheckResult {
size_type undefined_size;
size_type defined_size;
};
/**
* Check and classify the given offset. Returns a structure
* which tells you how much data is undefined, and how much
* data follows which is defined.
*/
CheckResult Check(size_type offset) const noexcept;
/**
* Commit a write: mark the given range in the buffer as
* "defined".
*/
void Commit(size_type start_offset, size_type end_offset) noexcept;
private:
size_type GetEndOffset() const noexcept {
return std::prev(map.end())->second;
}
Iterator CheckCollapsePrevious(Iterator i) noexcept;
Iterator CheckCollapseNext(Iterator i) noexcept;
};
/**
* A buffer which caches the contents of a "huge" array, and remembers
* which chunks are available.
*/
template<typename T>
class SparseBuffer {
using Buffer = HugeArray<T>;
using size_type = typename Buffer::size_type;
Buffer buffer;
SparseMap map;
public:
explicit SparseBuffer(size_type size)
:buffer(size), map(size) {
buffer.ForkCow(false);
}
size_type size() const noexcept {
return map.size();
}
struct ReadResult {
size_type undefined_size;
ConstBuffer<T> defined_buffer;
constexpr bool HasData() const noexcept {
return undefined_size == 0 &&
!defined_buffer.empty();
}
};
ReadResult Read(size_type offset) const noexcept {
auto c = map.Check(offset);
return {c.undefined_size, {&buffer.front() + offset + c.undefined_size, c.defined_size}};
}
WritableBuffer<T> Write(size_type offset) noexcept {
auto c = map.Check(offset);
return {&buffer.front() + offset, c.undefined_size};
}
void Commit(size_type start_offset, size_type end_offset) noexcept {
map.Commit(start_offset, end_offset);
}
};
#endif
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