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// Copyright 2015 Google 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.
//
////////////////////////////////////////////////////////////////////////////////
//
// The cache layer works as follows:
// The cache is implemented as a vector (of size 'cache_size') of shared
// pointers to pages recently used. The least recently used page is stored
// at the begining of the vector, the most recent at the end.
#include "src/binary_parse/cached_paged_byte_array.h"
#include <cstddef>
namespace piex {
namespace binary_parse {
CachedPagedByteArray::CachedPagedByteArray(
const PagedByteArray* paged_byte_array, size_t cache_size)
: paged_byte_array_(paged_byte_array), cache_size_(cache_size) {}
void CachedPagedByteArray::getPage(size_t page_index,
const unsigned char** begin,
const unsigned char** end,
PagedByteArray::PagePtr* page) const {
std::lock_guard<std::mutex> lock(mutex_);
size_t cache_index;
if (getFromCache(page_index, &cache_index)) {
// Cache hit, retrieve the page from the cache.
*begin = cached_pages_[cache_index].begin;
*end = cached_pages_[cache_index].end;
*page = cached_pages_[cache_index].page;
// Remove the page to insert it at the end of the cache later.
cached_pages_.erase(cached_pages_.begin() +
static_cast<std::ptrdiff_t>(cache_index));
} else {
// Cache miss, ask PagedByteArray to load the page.
paged_byte_array_->getPage(page_index, begin, end, page);
// If the cache is full, remove the first (least recently used) page.
if (cached_pages_.size() >= cache_size_) {
cached_pages_.erase(cached_pages_.begin());
}
}
// Cache the most recently used page to the end of the vector.
CachedPage cache_page;
cache_page.index = page_index;
cache_page.page = *page;
cache_page.begin = *begin;
cache_page.end = *end;
cached_pages_.push_back(cache_page);
}
bool CachedPagedByteArray::getFromCache(size_t page_index,
size_t* cache_index) const {
for (size_t i = 0; i < cached_pages_.size(); ++i) {
if (cached_pages_[i].index == page_index) {
*cache_index = i;
return true;
}
}
return false;
}
} // namespace binary_parse
} // namespace piex
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