mirror of https://github.com/facebook/rocksdb.git
104 lines
4.0 KiB
C++
104 lines
4.0 KiB
C++
// Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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#pragma once
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#include <array>
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#include <cstdint>
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#include <memory>
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#include <type_traits>
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#include "rocksdb/cache.h"
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#include "util/hash_containers.h"
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namespace ROCKSDB_NAMESPACE {
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extern std::array<std::string, kNumCacheEntryRoles>
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kCacheEntryRoleToCamelString;
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extern std::array<std::string, kNumCacheEntryRoles>
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kCacheEntryRoleToHyphenString;
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// To associate cache entries with their role, we use a hack on the
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// existing Cache interface. Because the deleter of an entry can authenticate
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// the code origin of an entry, we can elaborate the choice of deleter to
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// also encode role information, without inferring false role information
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// from entries not choosing to encode a role.
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//
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// The rest of this file is for handling mappings between deleters and
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// roles.
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// To infer a role from a deleter, the deleter must be registered. This
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// can be done "manually" with this function. This function is thread-safe,
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// and the registration mappings go into private but static storage. (Note
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// that DeleterFn is a function pointer, not std::function. Registrations
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// should not be too many.)
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void RegisterCacheDeleterRole(Cache::DeleterFn fn, CacheEntryRole role);
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// Gets a copy of the registered deleter -> role mappings. This is the only
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// function for reading the mappings made with RegisterCacheDeleterRole.
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// Why only this interface for reading?
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// * This function has to be thread safe, which could incur substantial
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// overhead. We should not pay this overhead for every deleter look-up.
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// * This is suitable for preparing for batch operations, like with
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// CacheEntryStatsCollector.
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// * The number of mappings should be sufficiently small (dozens).
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UnorderedMap<Cache::DeleterFn, CacheEntryRole> CopyCacheDeleterRoleMap();
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// ************************************************************** //
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// An automatic registration infrastructure. This enables code
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// to simply ask for a deleter associated with a particular type
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// and role, and registration is automatic. In a sense, this is
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// a small dependency injection infrastructure, because linking
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// in new deleter instantiations is essentially sufficient for
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// making stats collection (using CopyCacheDeleterRoleMap) aware
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// of them.
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namespace cache_entry_roles_detail {
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template <typename T, CacheEntryRole R>
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struct RegisteredDeleter {
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RegisteredDeleter() { RegisterCacheDeleterRole(Delete, R); }
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// These have global linkage to help ensure compiler optimizations do not
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// break uniqueness for each <T,R>
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static void Delete(const Slice& /* key */, void* value) {
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// Supports T == Something[], unlike delete operator
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std::default_delete<T>()(
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static_cast<typename std::remove_extent<T>::type*>(value));
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}
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};
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template <CacheEntryRole R>
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struct RegisteredNoopDeleter {
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RegisteredNoopDeleter() { RegisterCacheDeleterRole(Delete, R); }
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static void Delete(const Slice& /* key */, void* /* value */) {
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// Here was `assert(value == nullptr);` but we can also put pointers
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// to static data in Cache, for testing at least.
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}
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};
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} // namespace cache_entry_roles_detail
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// Get an automatically registered deleter for value type T and role R.
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// Based on C++ semantics, registration is invoked exactly once in a
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// thread-safe way on first call to this function, for each <T, R>.
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template <typename T, CacheEntryRole R>
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Cache::DeleterFn GetCacheEntryDeleterForRole() {
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static cache_entry_roles_detail::RegisteredDeleter<T, R> reg;
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return reg.Delete;
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}
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// Get an automatically registered no-op deleter (value should be nullptr)
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// and associated with role R. This is used for Cache "reservation" entries
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// such as for WriteBufferManager.
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template <CacheEntryRole R>
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Cache::DeleterFn GetNoopDeleterForRole() {
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static cache_entry_roles_detail::RegisteredNoopDeleter<R> reg;
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return reg.Delete;
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}
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} // namespace ROCKSDB_NAMESPACE
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