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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
#pragma once
#include <cassert>
#include "rocksdb/cache.h"
#include "rocksdb/rocksdb_namespace.h"
namespace ROCKSDB_NAMESPACE {
// Returns the cached value given a cache handle.
template <typename T>
T* GetFromCacheHandle(Cache* cache, Cache::Handle* handle) {
assert(cache);
assert(handle);
return static_cast<T*>(cache->Value(handle));
}
// Simple generic deleter for Cache (to be used with Cache::Insert).
template <typename T>
void DeleteCacheEntry(const Slice& /* key */, void* value) {
delete static_cast<T*>(value);
}
// Turns a T* into a Slice so it can be used as a key with Cache.
template <typename T>
Slice GetSlice(const T* t) {
return Slice(reinterpret_cast<const char*>(t), sizeof(T));
}
// Generic resource management object for cache handles that releases the handle
// when destroyed. Has unique ownership of the handle, so copying it is not
// allowed, while moving it transfers ownership.
template <typename T>
class CacheHandleGuard {
public:
CacheHandleGuard() = default;
CacheHandleGuard(Cache* cache, Cache::Handle* handle)
: cache_(cache),
handle_(handle),
value_(GetFromCacheHandle<T>(cache, handle)) {
assert(cache_ && handle_ && value_);
}
CacheHandleGuard(const CacheHandleGuard&) = delete;
CacheHandleGuard& operator=(const CacheHandleGuard&) = delete;
CacheHandleGuard(CacheHandleGuard&& rhs) noexcept
: cache_(rhs.cache_), handle_(rhs.handle_), value_(rhs.value_) {
assert((!cache_ && !handle_ && !value_) || (cache_ && handle_ && value_));
rhs.ResetFields();
}
CacheHandleGuard& operator=(CacheHandleGuard&& rhs) noexcept {
if (this == &rhs) {
return *this;
}
ReleaseHandle();
cache_ = rhs.cache_;
handle_ = rhs.handle_;
value_ = rhs.value_;
assert((!cache_ && !handle_ && !value_) || (cache_ && handle_ && value_));
rhs.ResetFields();
return *this;
}
~CacheHandleGuard() { ReleaseHandle(); }
bool IsEmpty() const { return !handle_; }
Cache* GetCache() const { return cache_; }
Cache::Handle* GetCacheHandle() const { return handle_; }
T* GetValue() const { return value_; }
void TransferTo(Cleanable* cleanable) {
if (cleanable) {
if (handle_ != nullptr) {
assert(cache_);
cleanable->RegisterCleanup(&ReleaseCacheHandle, cache_, handle_);
}
}
ResetFields();
}
void Reset() {
ReleaseHandle();
ResetFields();
}
private:
void ReleaseHandle() {
if (IsEmpty()) {
return;
}
assert(cache_);
cache_->Release(handle_);
}
void ResetFields() {
cache_ = nullptr;
handle_ = nullptr;
value_ = nullptr;
}
static void ReleaseCacheHandle(void* arg1, void* arg2) {
Cache* const cache = static_cast<Cache*>(arg1);
assert(cache);
Cache::Handle* const cache_handle = static_cast<Cache::Handle*>(arg2);
assert(cache_handle);
cache->Release(cache_handle);
}
private:
Cache* cache_ = nullptr;
Cache::Handle* handle_ = nullptr;
T* value_ = nullptr;
};
// Build an aliasing shared_ptr that keeps `handle` in cache while there
// are references, but the pointer is to the value for that cache entry,
// which must be of type T. This is copyable, unlike CacheHandleGuard, but
// does not provide access to caching details.
template <typename T>
std::shared_ptr<T> MakeSharedCacheHandleGuard(Cache* cache,
Cache::Handle* handle) {
auto wrapper = std::make_shared<CacheHandleGuard<T>>(cache, handle);
return std::shared_ptr<T>(wrapper, static_cast<T*>(cache->Value(handle)));
}
} // namespace ROCKSDB_NAMESPACE
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