mirror of
https://github.com/Evolution-X/external_piex
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80 lines
2.8 KiB
C++
Executable File
80 lines
2.8 KiB
C++
Executable File
// Copyright 2015 Google Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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////////////////////////////////////////////////////////////////////////////////
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//
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// The cache layer works as follows:
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// The cache is implemented as a vector (of size 'cache_size') of shared
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// pointers to pages recently used. The least recently used page is stored
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// at the begining of the vector, the most recent at the end.
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#include "src/binary_parse/cached_paged_byte_array.h"
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#include <cstddef>
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namespace piex {
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namespace binary_parse {
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CachedPagedByteArray::CachedPagedByteArray(
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const PagedByteArray* paged_byte_array, size_t cache_size)
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: paged_byte_array_(paged_byte_array), cache_size_(cache_size) {}
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void CachedPagedByteArray::getPage(size_t page_index,
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const unsigned char** begin,
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const unsigned char** end,
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PagedByteArray::PagePtr* page) const {
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std::lock_guard<std::mutex> lock(mutex_);
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size_t cache_index;
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if (getFromCache(page_index, &cache_index)) {
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// Cache hit, retrieve the page from the cache.
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*begin = cached_pages_[cache_index].begin;
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*end = cached_pages_[cache_index].end;
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*page = cached_pages_[cache_index].page;
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// Remove the page to insert it at the end of the cache later.
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cached_pages_.erase(cached_pages_.begin() +
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static_cast<std::ptrdiff_t>(cache_index));
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} else {
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// Cache miss, ask PagedByteArray to load the page.
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paged_byte_array_->getPage(page_index, begin, end, page);
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// If the cache is full, remove the first (least recently used) page.
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if (cached_pages_.size() >= cache_size_) {
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cached_pages_.erase(cached_pages_.begin());
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}
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}
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// Cache the most recently used page to the end of the vector.
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CachedPage cache_page;
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cache_page.index = page_index;
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cache_page.page = *page;
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cache_page.begin = *begin;
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cache_page.end = *end;
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cached_pages_.push_back(cache_page);
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}
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bool CachedPagedByteArray::getFromCache(size_t page_index,
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size_t* cache_index) const {
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for (size_t i = 0; i < cached_pages_.size(); ++i) {
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if (cached_pages_[i].index == page_index) {
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*cache_index = i;
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return true;
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}
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}
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return false;
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}
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} // namespace binary_parse
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} // namespace piex
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