Adding upstream version 18.2.2.upstream/18.2.2

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 103 insertions, 0 deletions

diff --git a/src/rocksdb/cache/cache_entry_roles.h b/src/rocksdb/cache/cache_entry_roles.h
new file mode 100644
index 000000000..5a49fdfd4
--- /dev/null
+++ b/src/rocksdb/cache/cache_entry_roles.h
@@ -0,0 +1,103 @@
+//  Copyright (c) Facebook, Inc. and its affiliates. 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 <array>
+#include <cstdint>
+#include <memory>
+#include <type_traits>
+
+#include "rocksdb/cache.h"
+#include "util/hash_containers.h"
+
+namespace ROCKSDB_NAMESPACE {
+
+extern std::array<std::string, kNumCacheEntryRoles>
+    kCacheEntryRoleToCamelString;
+extern std::array<std::string, kNumCacheEntryRoles>
+    kCacheEntryRoleToHyphenString;
+
+// To associate cache entries with their role, we use a hack on the
+// existing Cache interface. Because the deleter of an entry can authenticate
+// the code origin of an entry, we can elaborate the choice of deleter to
+// also encode role information, without inferring false role information
+// from entries not choosing to encode a role.
+//
+// The rest of this file is for handling mappings between deleters and
+// roles.
+
+// To infer a role from a deleter, the deleter must be registered. This
+// can be done "manually" with this function. This function is thread-safe,
+// and the registration mappings go into private but static storage. (Note
+// that DeleterFn is a function pointer, not std::function. Registrations
+// should not be too many.)
+void RegisterCacheDeleterRole(Cache::DeleterFn fn, CacheEntryRole role);
+
+// Gets a copy of the registered deleter -> role mappings. This is the only
+// function for reading the mappings made with RegisterCacheDeleterRole.
+// Why only this interface for reading?
+// * This function has to be thread safe, which could incur substantial
+// overhead. We should not pay this overhead for every deleter look-up.
+// * This is suitable for preparing for batch operations, like with
+// CacheEntryStatsCollector.
+// * The number of mappings should be sufficiently small (dozens).
+UnorderedMap<Cache::DeleterFn, CacheEntryRole> CopyCacheDeleterRoleMap();
+
+// ************************************************************** //
+// An automatic registration infrastructure. This enables code
+// to simply ask for a deleter associated with a particular type
+// and role, and registration is automatic. In a sense, this is
+// a small dependency injection infrastructure, because linking
+// in new deleter instantiations is essentially sufficient for
+// making stats collection (using CopyCacheDeleterRoleMap) aware
+// of them.
+
+namespace cache_entry_roles_detail {
+
+template <typename T, CacheEntryRole R>
+struct RegisteredDeleter {
+  RegisteredDeleter() { RegisterCacheDeleterRole(Delete, R); }
+
+  // These have global linkage to help ensure compiler optimizations do not
+  // break uniqueness for each <T,R>
+  static void Delete(const Slice& /* key */, void* value) {
+    // Supports T == Something[], unlike delete operator
+    std::default_delete<T>()(
+        static_cast<typename std::remove_extent<T>::type*>(value));
+  }
+};
+
+template <CacheEntryRole R>
+struct RegisteredNoopDeleter {
+  RegisteredNoopDeleter() { RegisterCacheDeleterRole(Delete, R); }
+
+  static void Delete(const Slice& /* key */, void* /* value */) {
+    // Here was `assert(value == nullptr);` but we can also put pointers
+    // to static data in Cache, for testing at least.
+  }
+};
+
+}  // namespace cache_entry_roles_detail
+
+// Get an automatically registered deleter for value type T and role R.
+// Based on C++ semantics, registration is invoked exactly once in a
+// thread-safe way on first call to this function, for each <T, R>.
+template <typename T, CacheEntryRole R>
+Cache::DeleterFn GetCacheEntryDeleterForRole() {
+  static cache_entry_roles_detail::RegisteredDeleter<T, R> reg;
+  return reg.Delete;
+}
+
+// Get an automatically registered no-op deleter (value should be nullptr)
+// and associated with role R. This is used for Cache "reservation" entries
+// such as for WriteBufferManager.
+template <CacheEntryRole R>
+Cache::DeleterFn GetNoopDeleterForRole() {
+  static cache_entry_roles_detail::RegisteredNoopDeleter<R> reg;
+  return reg.Delete;
+}
+
+}  // namespace ROCKSDB_NAMESPACE