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119 lines
3.6 KiB
C++
119 lines
3.6 KiB
C++
// Copyright 2019 Roman Perepelitsa.
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//
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// This file is part of GitStatus.
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//
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// GitStatus is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// GitStatus is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
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#include "arena.h"
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#include <algorithm>
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#include <type_traits>
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#include "bits.h"
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#include "check.h"
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namespace gitstatus {
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namespace {
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size_t Clamp(size_t min, size_t val, size_t max) { return std::min(max, std::max(min, val)); }
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static const uintptr_t kSingularity = reinterpret_cast<uintptr_t>(&kSingularity);
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} // namespace
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// Triple singularity. We are all fucked.
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Arena::Block Arena::g_empty_block = {kSingularity, kSingularity, kSingularity};
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Arena::Arena(Arena::Options opt) : opt_(std::move(opt)), top_(&g_empty_block) {
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CHECK(opt_.min_block_size <= opt_.max_block_size);
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}
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Arena::Arena(Arena&& other) : Arena() { *this = std::move(other); }
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Arena::~Arena() {
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// See comments in Makefile for the reason sized deallocation is not used.
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for (const Block& b : blocks_) ::operator delete(reinterpret_cast<void*>(b.start));
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}
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Arena& Arena::operator=(Arena&& other) {
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if (this != &other) {
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// In case std::vector ever gets small object optimization.
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size_t idx = other.reusable_ ? other.top_ - other.blocks_.data() : 0;
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opt_ = other.opt_;
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blocks_ = std::move(other.blocks_);
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reusable_ = other.reusable_;
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top_ = reusable_ ? blocks_.data() + idx : &g_empty_block;
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other.blocks_.clear();
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other.reusable_ = 0;
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other.top_ = &g_empty_block;
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}
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return *this;
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}
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void Arena::Reuse(size_t num_blocks) {
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reusable_ = std::min(reusable_, num_blocks);
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for (size_t i = reusable_; i != blocks_.size(); ++i) {
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const Block& b = blocks_[i];
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// See comments in Makefile for the reason sized deallocation is not used.
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::operator delete(reinterpret_cast<void*>(b.start));
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}
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blocks_.resize(reusable_);
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if (reusable_) {
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top_ = blocks_.data();
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top_->tip = top_->start;
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} else {
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top_ = &g_empty_block;
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}
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}
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void Arena::AddBlock(size_t size, size_t alignment) {
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if (alignment > alignof(std::max_align_t)) {
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size += alignment - 1;
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} else {
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size = std::max(size, alignment);
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}
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if (size <= top_->size() && top_ < blocks_.data() + reusable_ - 1) {
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assert(blocks_.front().size() == top_->size());
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++top_;
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top_->tip = top_->start;
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return;
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}
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if (size <= opt_.max_alloc_threshold) {
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size =
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std::max(size, Clamp(opt_.min_block_size, NextPow2(top_->size() + 1), opt_.max_block_size));
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}
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auto p = reinterpret_cast<uintptr_t>(::operator new(size));
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blocks_.push_back(Block{p, p, p + size});
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if (reusable_) {
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if (size < blocks_.front().size()) {
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top_ = &blocks_.back();
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return;
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}
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if (size > blocks_.front().size()) reusable_ = 0;
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}
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std::swap(blocks_.back(), blocks_[reusable_]);
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top_ = &blocks_[reusable_++];
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}
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void* Arena::AllocateSlow(size_t size, size_t alignment) {
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assert(alignment && !(alignment & (alignment - 1)));
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AddBlock(size, alignment);
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assert(Align(top_->tip, alignment) + size <= top_->end);
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return Allocate(size, alignment);
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}
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} // namespace gitstatus
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