1 // Copyright 2015 Google Inc. 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // http://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 // 15 //////////////////////////////////////////////////////////////////////////////// 16 // 17 // The cache layer works as follows: 18 // The cache is implemented as a vector (of size 'cache_size') of shared 19 // pointers to pages recently used. The least recently used page is stored 20 // at the begining of the vector, the most recent at the end. 21 22 #include "src/binary_parse/cached_paged_byte_array.h" 23 24 #include <cstddef> 25 26 namespace piex { 27 namespace binary_parse { 28 CachedPagedByteArray(const PagedByteArray * paged_byte_array,size_t cache_size)29 CachedPagedByteArray::CachedPagedByteArray( 30 const PagedByteArray* paged_byte_array, size_t cache_size) 31 : paged_byte_array_(paged_byte_array), cache_size_(cache_size) {} 32 getPage(size_t page_index,const unsigned char ** begin,const unsigned char ** end,PagedByteArray::PagePtr * page) const33 void CachedPagedByteArray::getPage(size_t page_index, 34 const unsigned char** begin, 35 const unsigned char** end, 36 PagedByteArray::PagePtr* page) const { 37 std::lock_guard<std::mutex> lock(mutex_); 38 size_t cache_index; 39 if (getFromCache(page_index, &cache_index)) { 40 // Cache hit, retrieve the page from the cache. 41 *begin = cached_pages_[cache_index].begin; 42 *end = cached_pages_[cache_index].end; 43 *page = cached_pages_[cache_index].page; 44 45 // Remove the page to insert it at the end of the cache later. 46 cached_pages_.erase(cached_pages_.begin() + 47 static_cast<std::ptrdiff_t>(cache_index)); 48 } else { 49 // Cache miss, ask PagedByteArray to load the page. 50 paged_byte_array_->getPage(page_index, begin, end, page); 51 52 // If the cache is full, remove the first (least recently used) page. 53 if (cached_pages_.size() >= cache_size_) { 54 cached_pages_.erase(cached_pages_.begin()); 55 } 56 } 57 58 // Cache the most recently used page to the end of the vector. 59 CachedPage cache_page; 60 cache_page.index = page_index; 61 cache_page.page = *page; 62 cache_page.begin = *begin; 63 cache_page.end = *end; 64 cached_pages_.push_back(cache_page); 65 } 66 getFromCache(size_t page_index,size_t * cache_index) const67 bool CachedPagedByteArray::getFromCache(size_t page_index, 68 size_t* cache_index) const { 69 for (size_t i = 0; i < cached_pages_.size(); ++i) { 70 if (cached_pages_[i].index == page_index) { 71 *cache_index = i; 72 return true; 73 } 74 } 75 return false; 76 } 77 78 } // namespace binary_parse 79 } // namespace piex 80