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** Copyright 2011, The Android Open Source Project
** 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
** Unless required by applicable law or agreed to in writing, software
** distributed under the License is distributed on an "AS IS" BASIS,
** See the License for the specific language governing permissions and
** limitations under the License.
#include "BlobCache.h"
#include <functional>
#include <memory>
#include <mutex>
#include <string>
// ----------------------------------------------------------------------------
namespace android {
// ----------------------------------------------------------------------------
class NNCache {
typedef BlobCache::Select Select;
typedef BlobCache::Capacity Capacity;
typedef BlobCache::Policy Policy;
static Policy defaultPolicy() { return BlobCache::defaultPolicy(); }
// get returns a pointer to the singleton NNCache object. This
// singleton object will never be destroyed.
static NNCache* get();
// initialize puts the NNCache into an initialized state, such
// that it is able to insert and retrieve entries from the cache.
// When not in the initialized state the getBlob and setBlob
// methods will return without performing any cache operations.
// The NNCache will cache key/value pairs with key and value sizes
// less than or equal to maxKeySize and maxValueSize,
// respectively. The total combined size of ALL cache entries (key
// sizes plus value sizes) will not exceed maxTotalSize.
void initialize(size_t maxKeySize, size_t maxValueSize, size_t maxTotalSize,
Policy policy = defaultPolicy());
// terminate puts the NNCache back into the uninitialized state. When
// in this state the getBlob and setBlob methods will return without
// performing any cache operations.
void terminate();
// setBlob attempts to insert a new key/value blob pair into the cache.
void setBlob(const void* key, ssize_t keySize, const void* value, ssize_t valueSize);
// getBlob attempts to retrieve the value blob associated with a given key
// blob from cache.
ssize_t getBlob(const void* key, ssize_t keySize, void* value, ssize_t valueSize);
ssize_t getBlob(const void* key, ssize_t keySize, void** value,
std::function<void*(size_t)> alloc);
template <typename T>
ssize_t getBlob(const void* key, size_t keySize, T** value,
std::function<void*(size_t)> alloc) {
void* valueVoid;
const ssize_t size = getBlob(key, keySize, &valueVoid, alloc);
*value = static_cast<T*>(valueVoid);
return size;
// setCacheFilename sets the name of the file that should be used to store
// cache contents from one program invocation to another.
void setCacheFilename(const char* filename);
// Creation and (the lack of) destruction is handled internally.
// Copying is disallowed.
NNCache(const NNCache&) = delete;
void operator=(const NNCache&) = delete;
// getBlobCacheLocked returns the BlobCache object being used to store the
// key/value blob pairs. If the BlobCache object has not yet been created,
// this will do so, loading the serialized cache contents from disk if
// possible.
BlobCache* getBlobCacheLocked();
// saveBlobCache attempts to save the current contents of mBlobCache to
// disk.
void saveBlobCacheLocked();
// loadBlobCache attempts to load the saved cache contents from disk into
// mBlobCache.
void loadBlobCacheLocked();
// mInitialized indicates whether the NNCache is in the initialized
// state. It is initialized to false at construction time, and gets set to
// true when initialize is called. It is set back to false when terminate
// is called. When in this state, the cache behaves as normal. When not,
// the getBlob and setBlob methods will return without performing any cache
// operations.
bool mInitialized;
// mMaxKeySize is the maximum key size that will be cached.
size_t mMaxKeySize;
// mMaxValueSize is the maximum value size that will be cached.
size_t mMaxValueSize;
// mMaxTotalSize is the maximum size that all cache entries can occupy. This
// includes space for both keys and values.
size_t mMaxTotalSize;
// mPolicy is the policy for cleaning the cache.
Policy mPolicy;
// mBlobCache is the cache in which the key/value blob pairs are stored. It
// is initially NULL, and will be initialized by getBlobCacheLocked the
// first time it's needed.
std::unique_ptr<BlobCache> mBlobCache;
// mFilename is the name of the file for storing cache contents in between
// program invocations. It is initialized to an empty string at
// construction time, and can be set with the setCacheFilename method. An
// empty string indicates that the cache should not be saved to or restored
// from disk.
std::string mFilename;
// mSavePending indicates whether or not a deferred save operation is
// pending. Each time a key/value pair is inserted into the cache via
// setBlob, a deferred save is initiated if one is not already pending.
// This will wait some amount of time and then trigger a save of the cache
// contents to disk.
bool mSavePending;
// mMutex is the mutex used to prevent concurrent access to the member
// variables. It must be locked whenever the member variables are accessed.
mutable std::mutex mMutex;
// sCache is the singleton NNCache object.
static NNCache sCache;
// ----------------------------------------------------------------------------
}; // namespace android
// ----------------------------------------------------------------------------