New caching store is working, but not timeout-flushing yet

implementations/caching2/Cache.cpp

@@ -0,0 +1,50 @@
+#include "Cache.h"
+
+using std::unique_ptr;
+using std::make_unique;
+using std::mutex;
+using std::lock_guard;
+using std::pair;
+
+namespace blockstore {
+namespace caching2 {
+
+constexpr uint32_t Cache::MAX_ENTRIES;
+
+Cache::Cache(): _cachedBlocks() {
+}
+
+Cache::~Cache() {
+}
+
+unique_ptr<Block> Cache::pop(const Key &key) {
+  lock_guard<mutex> lock(_mutex);
+  auto found = _cachedBlocks.find(key);
+  if (found == _cachedBlocks.end()) {
+    return nullptr;
+  }
+  auto block = found->second.releaseBlock();
+  _cachedBlocks.erase(found);
+  return block;
+}
+
+void Cache::push(unique_ptr<Block> block) {
+  lock_guard<mutex> lock(_mutex);
+  if (_cachedBlocks.size() > MAX_ENTRIES) {
+    deleteOldestEntry();
+    assert(_cachedBlocks.size() == MAX_ENTRIES-1);
+  }
+  Key key = block->key();
+  _cachedBlocks.emplace(key, std::move(block));
+}
+
+void Cache::deleteOldestEntry() {
+  auto oldestEntry = std::min_element(_cachedBlocks.begin(), _cachedBlocks.end(), [] (const pair<const Key, CacheEntry> &lhs, const pair<const Key, CacheEntry> &rhs) {
+    return lhs.second.ageSeconds() > rhs.second.ageSeconds();
+  });
+  //printf("Deleting age %f (vs %f)\n", oldestEntry->second.ageSeconds(), _cachedBlocks.begin()->second.ageSeconds());
+  _cachedBlocks.erase(oldestEntry);
+}
+
+}
+}

implementations/caching2/Cache.h

@@ -0,0 +1,33 @@
+#pragma once
+#ifndef MESSMER_BLOCKSTORE_IMPLEMENTATIONS_CACHING2_CACHE_H_
+#define MESSMER_BLOCKSTORE_IMPLEMENTATIONS_CACHING2_CACHE_H_
+
+#include "../../interface/Block.h"
+#include "CacheEntry.h"
+#include <memory>
+#include <mutex>
+
+namespace blockstore {
+namespace caching2 {
+
+class Cache {
+public:
+  static constexpr uint32_t MAX_ENTRIES = 1000;
+
+  Cache();
+  virtual ~Cache();
+
+  void push(std::unique_ptr<Block> block);
+  std::unique_ptr<Block> pop(const Key &key);
+
+private:
+  mutable std::mutex _mutex;
+  std::map<Key, CacheEntry> _cachedBlocks;
+
+  void deleteOldestEntry();
+};
+
+}
+}
+
+#endif

implementations/caching2/CacheEntry.h

@@ -15,7 +15,9 @@ public:
   CacheEntry(std::unique_ptr<Block> block): _lastAccess(time(nullptr)), _block(std::move(block)) {
   }
 
-  double ageSeconds() {
+  CacheEntry(CacheEntry &&) = default;
+
+  double ageSeconds() const {
     return difftime(time(nullptr), _lastAccess);
   }
 

implementations/caching2/CachedBlock.cpp

@@ -0,0 +1,36 @@
+#include "CachedBlock.h"
+#include "Caching2BlockStore.h"
+
+using std::make_unique;
+
+namespace blockstore {
+namespace caching2 {
+
+CachedBlock::CachedBlock(std::unique_ptr<Block> baseBlock, Caching2BlockStore *blockStore)
+    :Block(baseBlock->key()),
+     _blockStore(blockStore),
+     _baseBlock(std::move(baseBlock)) {
+}
+
+CachedBlock::~CachedBlock() {
+  _blockStore->release(std::move(_baseBlock));
+}
+
+const void *CachedBlock::data() const {
+  return _baseBlock->data();
+}
+
+void CachedBlock::write(const void *source, uint64_t offset, uint64_t size) {
+  return _baseBlock->write(source, offset, size);
+}
+
+void CachedBlock::flush() {
+  return _baseBlock->flush();
+}
+
+size_t CachedBlock::size() const {
+  return _baseBlock->size();
+}
+
+}
+}

implementations/caching2/CachedBlock.h

@@ -0,0 +1,36 @@
+#pragma once
+#ifndef BLOCKSTORE_IMPLEMENTATIONS_ENCRYPTED_ENCRYPTEDBLOCK_H_
+#define BLOCKSTORE_IMPLEMENTATIONS_ENCRYPTED_ENCRYPTEDBLOCK_H_
+
+#include "../../interface/Block.h"
+
+#include "messmer/cpp-utils/macros.h"
+#include <memory>
+
+namespace blockstore {
+namespace caching2 {
+class Caching2BlockStore;
+
+class CachedBlock: public Block {
+public:
+  //TODO Storing key twice (in parent class and in object pointed to). Once would be enough.
+  CachedBlock(std::unique_ptr<Block> baseBlock, Caching2BlockStore *blockStore);
+  virtual ~CachedBlock();
+
+  const void *data() const override;
+  void write(const void *source, uint64_t offset, uint64_t size) override;
+  void flush() override;
+
+  size_t size() const override;
+
+private:
+  Caching2BlockStore *_blockStore;
+  std::unique_ptr<Block> _baseBlock;
+
+  DISALLOW_COPY_AND_ASSIGN(CachedBlock);
+};
+
+}
+}
+
+#endif

implementations/caching2/Caching2BlockStore.cpp

@@ -1,7 +1,11 @@
 #include "Caching2BlockStore.h"
+#include "CachedBlock.h"
 #include "../../interface/Block.h"
 
+#include <algorithm>
+
 using std::unique_ptr;
+using std::make_unique;
 
 namespace blockstore {
 namespace caching2 {
@@ -15,11 +19,15 @@ unique_ptr<Block> Caching2BlockStore::create(size_t size) {
   //     When writing back is done efficiently in the base store (e.g. only one safe-to-disk, not one in the create() and then one in the save(), this is not supported by the current BlockStore interface),
   //     then the base store could actually directly create a block in the create() call, OnDiskBlockStore wouldn't have to avoid file creation in the create() call for performance reasons and I could also adapt the OnDiskBlockStore test cases and remove a lot of flush() calls there because then blocks are loadable directly after the create call() without a flush.
   //     Currently, OnDiskBlockStore doesn't create new blocks directly but only after they're destructed (performance reasons), but this means a newly created block can't be loaded directly.
-  return _baseBlockStore->create(size);
+  return make_unique<CachedBlock>(_baseBlockStore->create(size), this);
 }
 
 unique_ptr<Block> Caching2BlockStore::load(const Key &key) {
-  return _baseBlockStore->load(key);
+  auto block = _cache.pop(key);
+  if (block.get() != nullptr) {
+    return make_unique<CachedBlock>(std::move(block), this);
+  }
+  return make_unique<CachedBlock>(_baseBlockStore->load(key), this);
 }
 
 void Caching2BlockStore::remove(std::unique_ptr<Block> block) {
@@ -30,5 +38,9 @@ uint64_t Caching2BlockStore::numBlocks() const {
   return _baseBlockStore->numBlocks();
 }
 
+void Caching2BlockStore::release(unique_ptr<Block> block) {
+  _cache.push(std::move(block));
+}
+
 }
 }

implementations/caching2/Caching2BlockStore.h

@@ -3,7 +3,7 @@
 #define BLOCKSTORE_IMPLEMENTATIONS_CACHING2_CACHINGBLOCKSTORE_H_
 
 #include "../../interface/BlockStore.h"
-#include "CacheEntry.h"
+#include "Cache.h"
 
 namespace blockstore {
 namespace caching2 {
@@ -17,10 +17,11 @@ public:
   void remove(std::unique_ptr<Block> block) override;
   uint64_t numBlocks() const override;
 
-private:
+  void release(std::unique_ptr<Block> block);
 
+private:
   std::unique_ptr<BlockStore> _baseBlockStore;
-  std::map<Key, CacheEntry> _cachedBlocks;
+  Cache _cache;
 
   DISALLOW_COPY_AND_ASSIGN(Caching2BlockStore);
 };