Meta-internal folly integration with F14FastMap (facebook#9546)

Summary:
Especially after updating to C++17, I don't see a compelling case for
*requiring* any folly components in RocksDB. I was able to purge the existing
hard dependencies, and it can be quite difficult to strip out non-trivial components
from folly for use in RocksDB. (The prospect of doing that on F14 has changed
my mind on the best approach here.)

But this change creates an optional integration where we can plug in
components from folly at compile time, starting here with F14FastMap to replace
std::unordered_map when possible (probably no public APIs for example). I have
replaced the biggest CPU users of std::unordered_map with compile-time
pluggable UnorderedMap which will use F14FastMap when USE_FOLLY is set.
USE_FOLLY is always set in the Meta-internal buck build, and a simulation of
that is in the Makefile for public CI testing. A full folly build is not needed, but
checking out the full folly repo is much simpler for getting the dependency,
and anything else we might want to optionally integrate in the future.

Some picky details:
* I don't think the distributed mutex stuff is actually used, so it was easy to remove.
* I implemented an alternative to `folly::constexpr_log2` (which is much easier
in C++17 than C++11) so that I could pull out the hard dependencies on
`ConstexprMath.h`
* I had to add noexcept move constructors/operators to some types to make
F14's complainUnlessNothrowMoveAndDestroy check happy, and I added a
macro to make that easier in some common cases.
* Updated Meta-internal buck build to use folly F14Map (always)

No updates to HISTORY.md nor INSTALL.md as this is not (yet?) considered a
production integration for open source users.

Pull Request resolved: facebook#9546

Test Plan:
CircleCI tests updated so that a couple of them use folly.

Most internal unit & stress/crash tests updated to use Meta-internal latest folly.
(Note: they should probably use buck but they currently use Makefile.)

Example performance improvement: when filter partitions are pinned in cache,
they are tracked by PartitionedFilterBlockReader::filter_map_ and we can build
a test that exercises that heavily. Build DB with

```
TEST_TMPDIR=/dev/shm/rocksdb ./db_bench -benchmarks=fillrandom -num=10000000 -disable_wal=1 -write_buffer_size=30000000 -bloom_bits=16 -compaction_style=2 -fifo_compaction_max_table_files_size_mb=10000 -fifo_compaction_allow_compaction=0 -partition_index_and_filters
```

and test with (simultaneous runs with & without folly, ~20 times each to see
convergence)

```
TEST_TMPDIR=/dev/shm/rocksdb ./db_bench_folly -readonly -use_existing_db -benchmarks=readrandom -num=10000000 -bloom_bits=16 -compaction_style=2 -fifo_compaction_max_table_files_size_mb=10000 -fifo_compaction_allow_compaction=0 -partition_index_and_filters -duration=40 -pin_l0_filter_and_index_blocks_in_cache
```

Average ops/s no folly: 26229.2
Average ops/s with folly: 26853.3 (+2.4%)

Reviewed By: ajkr

Differential Revision: D34181736

Pulled By: pdillinger

fbshipit-source-id: ffa6ad5104c2880321d8a1aa7187e00ab0d02e94

.circleci/config.yml

@@ -368,18 +368,19 @@ jobs:
       - run: CC=clang-10 CXX=clang++-10 ROCKSDB_DISABLE_ALIGNED_NEW=1 CLANG_ANALYZER="/usr/bin/clang++-10" CLANG_SCAN_BUILD=scan-build-10 USE_CLANG=1 make V=1 -j32 analyze # aligned new doesn't work for reason we haven't figured out. For unknown, reason passing "clang++-10" as CLANG_ANALYZER doesn't work, and we need a full path.
       - post-steps
 
-  build-linux-cmake:
+  build-linux-cmake-with-folly:
     machine:
       image: ubuntu-2004:202111-02
     resource_class: 2xlarge
     steps:
       - pre-steps
       - install-gflags
       - upgrade-cmake
-      - run: (mkdir build && cd build && cmake -DWITH_GFLAGS=1 .. && make V=1 -j20 && ctest -j20)
+      - run: make checkout_folly
+      - run: (mkdir build && cd build && cmake -DUSE_FOLLY=1 -DWITH_GFLAGS=1 .. && make V=1 -j20 && ctest -j20)
       - post-steps
 
-  build-linux-cmake-ubuntu-20:
+  build-linux-cmake-with-benchmark:
     machine:
       image: ubuntu-2004:202111-02
     resource_class: 2xlarge
@@ -401,14 +402,15 @@ jobs:
       - run: make V=1 -j8 -k check-headers # could be moved to a different build
       - post-steps
 
-  build-linux-gcc-7:
+  build-linux-gcc-7-with-folly:
     machine:
       image: ubuntu-2004:202111-02
     resource_class: 2xlarge
     steps:
       - pre-steps
       - run: sudo add-apt-repository -y ppa:ubuntu-toolchain-r/test && sudo apt-get update -y && sudo apt-get install gcc-7 g++-7 libgflags-dev
-      - run: CC=gcc-7 CXX=g++-7 V=1 make -j32 check
+      - run: make checkout_folly
+      - run: USE_FOLLY=1 CC=gcc-7 CXX=g++-7 V=1 make -j32 check
       - post-steps
 
   build-linux-gcc-8-no_test_run:
@@ -799,8 +801,8 @@ workflows:
       - build-linux
   build-linux-cmake:
     jobs:
-      - build-linux-cmake
-      - build-linux-cmake-ubuntu-20
+      - build-linux-cmake-with-folly
+      - build-linux-cmake-with-benchmark
   build-linux-encrypted-env:
     jobs:
       - build-linux-encrypted-env
@@ -871,7 +873,7 @@ workflows:
     jobs:
       - build-linux-clang-no_test_run
       - build-linux-clang-13-no_test_run
-      - build-linux-gcc-7
+      - build-linux-gcc-7-with-folly
       - build-linux-gcc-8-no_test_run
       - build-linux-gcc-10-cxx20-no_test_run
       - build-linux-gcc-11-no_test_run

.gitignore

@@ -95,3 +95,4 @@ fuzz/proto/gen/
 fuzz/crash-*
 
 cmake-build-*
+third-party/folly/

CMakeLists.txt

@@ -78,19 +78,6 @@ if ($ENV{CIRCLECI})
   add_definitions(-DCIRCLECI)
 endif()
 
-# third-party/folly is only validated to work on Linux and Windows for now.
-# So only turn it on there by default.
-if(CMAKE_SYSTEM_NAME MATCHES "Linux|Windows")
-  if(MSVC AND MSVC_VERSION LESS 1910)
-    # Folly does not compile with MSVC older than VS2017
-    option(WITH_FOLLY_DISTRIBUTED_MUTEX "build with folly::DistributedMutex" OFF)
-  else()
-    option(WITH_FOLLY_DISTRIBUTED_MUTEX "build with folly::DistributedMutex" ON)
-  endif()
-else()
-  option(WITH_FOLLY_DISTRIBUTED_MUTEX "build with folly::DistributedMutex" OFF)
-endif()
-
 if( NOT DEFINED CMAKE_CXX_STANDARD )
   set(CMAKE_CXX_STANDARD 17)
 endif()
@@ -594,8 +581,9 @@ endif()
 
 include_directories(${PROJECT_SOURCE_DIR})
 include_directories(${PROJECT_SOURCE_DIR}/include)
-if(WITH_FOLLY_DISTRIBUTED_MUTEX)
+if(USE_FOLLY)
   include_directories(${PROJECT_SOURCE_DIR}/third-party/folly)
+  add_definitions(-DUSE_FOLLY -DFOLLY_NO_CONFIG)
 endif()
 find_package(Threads REQUIRED)
 
@@ -977,13 +965,12 @@ else()
     env/io_posix.cc)
 endif()
 
-if(WITH_FOLLY_DISTRIBUTED_MUTEX)
+if(USE_FOLLY)
   list(APPEND SOURCES
-    third-party/folly/folly/detail/Futex.cpp
-    third-party/folly/folly/synchronization/AtomicNotification.cpp
-    third-party/folly/folly/synchronization/DistributedMutex.cpp
-    third-party/folly/folly/synchronization/ParkingLot.cpp
-    third-party/folly/folly/synchronization/WaitOptions.cpp)
+    third-party/folly/folly/container/detail/F14Table.cpp
+    third-party/folly/folly/lang/SafeAssert.cpp
+    third-party/folly/folly/lang/ToAscii.cpp
+    third-party/folly/folly/ScopeGuard.cpp)
 endif()
 
 set(ROCKSDB_STATIC_LIB rocksdb${ARTIFACT_SUFFIX})
@@ -1379,10 +1366,6 @@ if(WITH_TESTS)
     )
   endif()
 
-  if(WITH_FOLLY_DISTRIBUTED_MUTEX)
-    list(APPEND TESTS third-party/folly/folly/synchronization/test/DistributedMutexTest.cpp)
-  endif()
-
   set(TESTUTIL_SOURCE
       db/db_test_util.cc
       monitoring/thread_status_updater_debug.cc

Makefile

@@ -400,6 +400,10 @@ ifndef DISABLE_JEMALLOC
 	ifdef JEMALLOC
 		PLATFORM_CXXFLAGS += -DROCKSDB_JEMALLOC -DJEMALLOC_NO_DEMANGLE
 		PLATFORM_CCFLAGS  += -DROCKSDB_JEMALLOC -DJEMALLOC_NO_DEMANGLE
+		ifeq ($(USE_FOLLY),1)
+			PLATFORM_CXXFLAGS += -DUSE_JEMALLOC
+			PLATFORM_CCFLAGS  += -DUSE_JEMALLOC
+		endif
 	endif
 	ifdef WITH_JEMALLOC_FLAG
 		PLATFORM_LDFLAGS += -ljemalloc
@@ -410,8 +414,8 @@ ifndef DISABLE_JEMALLOC
 	PLATFORM_CCFLAGS += $(JEMALLOC_INCLUDE)
 endif
 
-ifndef USE_FOLLY_DISTRIBUTED_MUTEX
-	USE_FOLLY_DISTRIBUTED_MUTEX=0
+ifndef USE_FOLLY
+	USE_FOLLY=0
 endif
 
 ifndef GTEST_THROW_ON_FAILURE
@@ -431,8 +435,12 @@ else
 	PLATFORM_CXXFLAGS += -isystem $(GTEST_DIR)
 endif
 
-ifeq ($(USE_FOLLY_DISTRIBUTED_MUTEX),1)
-	FOLLY_DIR = ./third-party/folly
+# This provides a Makefile simulation of a Meta-internal folly integration.
+# It is not validated for general use.
+ifeq ($(USE_FOLLY),1)
+	ifeq (,$(FOLLY_DIR))
+		FOLLY_DIR = ./third-party/folly
+	endif
 	# AIX: pre-defined system headers are surrounded by an extern "C" block
 	ifeq ($(PLATFORM), OS_AIX)
 		PLATFORM_CCFLAGS += -I$(FOLLY_DIR)
@@ -441,6 +449,8 @@ ifeq ($(USE_FOLLY_DISTRIBUTED_MUTEX),1)
 		PLATFORM_CCFLAGS += -isystem $(FOLLY_DIR)
 		PLATFORM_CXXFLAGS += -isystem $(FOLLY_DIR)
 	endif
+	PLATFORM_CCFLAGS += -DUSE_FOLLY -DFOLLY_NO_CONFIG
+	PLATFORM_CXXFLAGS += -DUSE_FOLLY -DFOLLY_NO_CONFIG
 endif
 
 ifdef TEST_CACHE_LINE_SIZE
@@ -527,7 +537,7 @@ LIB_OBJECTS += $(patsubst %.c, $(OBJ_DIR)/%.o, $(LIB_SOURCES_C))
 LIB_OBJECTS += $(patsubst %.S, $(OBJ_DIR)/%.o, $(LIB_SOURCES_ASM))
 endif
 
-ifeq ($(USE_FOLLY_DISTRIBUTED_MUTEX),1)
+ifeq ($(USE_FOLLY),1)
   LIB_OBJECTS += $(patsubst %.cpp, $(OBJ_DIR)/%.o, $(FOLLY_SOURCES))
 endif
 
@@ -562,11 +572,6 @@ ALL_SOURCES += $(ROCKSDB_PLUGIN_SOURCES)
 TESTS = $(patsubst %.cc, %, $(notdir $(TEST_MAIN_SOURCES)))
 TESTS += $(patsubst %.c, %, $(notdir $(TEST_MAIN_SOURCES_C)))
 
-ifeq ($(USE_FOLLY_DISTRIBUTED_MUTEX),1)
-	TESTS += folly_synchronization_distributed_mutex_test
-	ALL_SOURCES += third-party/folly/folly/synchronization/test/DistributedMutexTest.cc
-endif
-
 # `make check-headers` to very that each header file includes its own
 # dependencies
 ifneq ($(filter check-headers, $(MAKECMDGOALS)),)
@@ -791,7 +796,7 @@ endif  # PLATFORM_SHARED_EXT
 .PHONY: blackbox_crash_test check clean coverage crash_test ldb_tests package \
 	release tags tags0 valgrind_check whitebox_crash_test format static_lib shared_lib all \
 	dbg rocksdbjavastatic rocksdbjava gen-pc install install-static install-shared uninstall \
-	analyze tools tools_lib check-headers \
+	analyze tools tools_lib check-headers checkout_folly \
 	blackbox_crash_test_with_atomic_flush whitebox_crash_test_with_atomic_flush  \
 	blackbox_crash_test_with_txn whitebox_crash_test_with_txn \
 	blackbox_crash_test_with_best_efforts_recovery \
@@ -1306,11 +1311,6 @@ trace_analyzer: $(OBJ_DIR)/tools/trace_analyzer.o $(ANALYZE_OBJECTS) $(TOOLS_LIB
 block_cache_trace_analyzer: $(OBJ_DIR)/tools/block_cache_analyzer/block_cache_trace_analyzer_tool.o $(ANALYZE_OBJECTS) $(TOOLS_LIBRARY) $(LIBRARY)
 	$(AM_LINK)
 
-ifeq ($(USE_FOLLY_DISTRIBUTED_MUTEX),1)
-folly_synchronization_distributed_mutex_test: $(OBJ_DIR)/third-party/folly/folly/synchronization/test/DistributedMutexTest.o $(TEST_LIBRARY) $(LIBRARY)
-	$(AM_LINK)
-endif
-
 cache_bench: $(OBJ_DIR)/cache/cache_bench.o $(CACHE_BENCH_OBJECTS) $(LIBRARY)
 	$(AM_LINK)
 
@@ -2383,6 +2383,22 @@ commit_prereq:
 	false # J=$(J) build_tools/precommit_checker.py unit clang_unit release clang_release tsan asan ubsan lite unit_non_shm
 	# $(MAKE) clean && $(MAKE) jclean && $(MAKE) rocksdbjava;
 
+# For public CI runs, checkout folly in a way that can build with RocksDB.
+# This is mostly intended as a test-only simulation of Meta-internal folly
+# integration.
+checkout_folly:
+	if [ -e third-party/folly ]; then \
+		cd third-party/folly && git fetch origin; \
+	else \
+		cd third-party && git clone https://github.com/facebook/folly.git; \
+	fi
+	@# Pin to a particular version for public CI, so that PR authors don't
+	@# need to worry about folly breaking our integration. Update periodically
+	cd third-party/folly && git reset --hard 98b9b2c1124e99f50f9085ddee74ce32afffc665
+	@# A hack to remove boost dependency.
+	@# NOTE: this hack is not needed if using FBCODE compiler config
+	perl -pi -e 's/^(#include <boost)/\/\/$$1/' third-party/folly/folly/functional/Invoke.h
+
 # ---------------------------------------------------------------------------
 #  	Platform-specific compilation
 # ---------------------------------------------------------------------------
@@ -2435,7 +2451,7 @@ endif
 ifneq ($(SKIP_DEPENDS), 1)
 DEPFILES = $(patsubst %.cc, $(OBJ_DIR)/%.cc.d, $(ALL_SOURCES))
 DEPFILES+ = $(patsubst %.c, $(OBJ_DIR)/%.c.d, $(LIB_SOURCES_C) $(TEST_MAIN_SOURCES_C))
-ifeq ($(USE_FOLLY_DISTRIBUTED_MUTEX),1)
+ifeq ($(USE_FOLLY),1)
   DEPFILES +=$(patsubst %.cpp, $(OBJ_DIR)/%.cpp.d, $(FOLLY_SOURCES))
 endif
 endif
@@ -2483,7 +2499,7 @@ list_all_tests:
 
 # Remove the rules for which dependencies should not be generated and see if any are left.
 #If so, include the dependencies; if not, do not include the dependency files
-ROCKS_DEP_RULES=$(filter-out clean format check-format check-buck-targets check-headers check-sources jclean jtest package analyze tags rocksdbjavastatic% unity.% unity_test, $(MAKECMDGOALS))
+ROCKS_DEP_RULES=$(filter-out clean format check-format check-buck-targets check-headers check-sources jclean jtest package analyze tags rocksdbjavastatic% unity.% unity_test checkout_folly, $(MAKECMDGOALS))
 ifneq ("$(ROCKS_DEP_RULES)", "")
 -include $(DEPFILES)
 endif

TARGETS

@@ -324,7 +324,7 @@ cpp_library_wrapper(name="rocksdb_lib", srcs=[
         "utilities/wal_filter.cc",
         "utilities/write_batch_with_index/write_batch_with_index.cc",
         "utilities/write_batch_with_index/write_batch_with_index_internal.cc",
-    ], deps=[], headers=None, link_whole=False, extra_test_libs=False)
+    ], deps=["//folly/container:f14_hash"], headers=None, link_whole=False, extra_test_libs=False)
 
 cpp_library_wrapper(name="rocksdb_whole_archive_lib", srcs=[
         "cache/cache.cc",
@@ -642,7 +642,7 @@ cpp_library_wrapper(name="rocksdb_whole_archive_lib", srcs=[
         "utilities/wal_filter.cc",
         "utilities/write_batch_with_index/write_batch_with_index.cc",
         "utilities/write_batch_with_index/write_batch_with_index_internal.cc",
-    ], deps=[], headers=None, link_whole=True, extra_test_libs=False)
+    ], deps=["//folly/container:f14_hash"], headers=None, link_whole=True, extra_test_libs=False)
 
 cpp_library_wrapper(name="rocksdb_test_lib", srcs=[
         "db/db_test_util.cc",

buckifier/buckify_rocksdb.py

@@ -143,15 +143,16 @@ def generate_targets(repo_path, deps_map):
         src_mk["LIB_SOURCES"] +
         # always add range_tree, it's only excluded on ppc64, which we don't use internally
         src_mk["RANGE_TREE_SOURCES"] +
-        src_mk["TOOL_LIB_SOURCES"])
+        src_mk["TOOL_LIB_SOURCES"],
+        deps=["//folly/container:f14_hash"])
     # rocksdb_whole_archive_lib
     TARGETS.add_library(
         "rocksdb_whole_archive_lib",
         src_mk["LIB_SOURCES"] +
         # always add range_tree, it's only excluded on ppc64, which we don't use internally
         src_mk["RANGE_TREE_SOURCES"] +
         src_mk["TOOL_LIB_SOURCES"],
-        deps=None,
+        deps=["//folly/container:f14_hash"],
         headers=None,
         extra_external_deps="",
         link_whole=True)

build_tools/build_detect_platform

@@ -874,8 +874,8 @@ if test -n "$WITH_JEMALLOC_FLAG"; then
   echo "WITH_JEMALLOC_FLAG=$WITH_JEMALLOC_FLAG" >> "$OUTPUT"
 fi
 echo "LUA_PATH=$LUA_PATH" >> "$OUTPUT"
-if test -n "$USE_FOLLY_DISTRIBUTED_MUTEX"; then
-  echo "USE_FOLLY_DISTRIBUTED_MUTEX=$USE_FOLLY_DISTRIBUTED_MUTEX" >> "$OUTPUT"
+if test -n "$USE_FOLLY"; then
+  echo "USE_FOLLY=$USE_FOLLY" >> "$OUTPUT"
 fi
 if test -n "$PPC_LIBC_IS_GNU"; then
   echo "PPC_LIBC_IS_GNU=$PPC_LIBC_IS_GNU" >> "$OUTPUT"

build_tools/dependencies_platform009.sh

@@ -19,3 +19,4 @@ BINUTILS_BASE=/mnt/gvfs/third-party2/binutils/08634589372fa5f237bfd374e8c644a836
 VALGRIND_BASE=/mnt/gvfs/third-party2/valgrind/6ae525939ad02e5e676855082fbbc7828dbafeac/3.15.0/platform009/7f3b187
 LUA_BASE=/mnt/gvfs/third-party2/lua/162efd9561a3d21f6869f4814011e9cf1b3ff4dc/5.3.4/platform009/a6271c4
 BENCHMARK_BASE=/mnt/gvfs/third-party2/benchmark/30bf49ad6414325e17f3425b0edcb64239427ae3/1.6.1/platform009/7f3b187
+BOOST_BASE=/mnt/gvfs/third-party2/boost/201b7d74941e54b436dfa364a063aa6d2cd7de4c/1.69.0/platform009/8a7ffdf

build_tools/fbcode_config.sh

@@ -162,6 +162,4 @@ else
   LUA_LIB=" $LUA_PATH/lib/liblua_pic.a"
 fi
 
-USE_FOLLY_DISTRIBUTED_MUTEX=1
-
 export CC CXX AR CFLAGS CXXFLAGS EXEC_LDFLAGS EXEC_LDFLAGS_SHARED VALGRIND_VER JEMALLOC_LIB JEMALLOC_INCLUDE CLANG_ANALYZER CLANG_SCAN_BUILD LUA_PATH LUA_LIB

build_tools/fbcode_config_platform009.sh

@@ -58,6 +58,8 @@ CFLAGS+=" -DGFLAGS=gflags"
 BENCHMARK_INCLUDE=" -I $BENCHMARK_BASE/include/"
 BENCHMARK_LIBS=" $BENCHMARK_BASE/lib/libbenchmark${MAYBE_PIC}.a"
 
+BOOST_INCLUDE=" -I $BOOST_BASE/include/"
+
 # location of jemalloc
 JEMALLOC_INCLUDE=" -I $JEMALLOC_BASE/include/"
 JEMALLOC_LIB=" $JEMALLOC_BASE/lib/libjemalloc${MAYBE_PIC}.a"
@@ -89,7 +91,7 @@ BINUTILS="$BINUTILS_BASE/bin"
 AR="$BINUTILS/ar"
 AS="$BINUTILS/as"
 
-DEPS_INCLUDE="$SNAPPY_INCLUDE $ZLIB_INCLUDE $BZIP_INCLUDE $LZ4_INCLUDE $ZSTD_INCLUDE $GFLAGS_INCLUDE $NUMA_INCLUDE $TBB_INCLUDE $LIBURING_INCLUDE $BENCHMARK_INCLUDE"
+DEPS_INCLUDE="$SNAPPY_INCLUDE $ZLIB_INCLUDE $BZIP_INCLUDE $LZ4_INCLUDE $ZSTD_INCLUDE $GFLAGS_INCLUDE $NUMA_INCLUDE $TBB_INCLUDE $LIBURING_INCLUDE $BENCHMARK_INCLUDE $BOOST_INCLUDE"
 
 STDLIBS="-L $GCC_BASE/lib64"
 

cache/cache_entry_roles.cc

@@ -43,12 +43,12 @@ namespace {
 
 struct Registry {
   std::mutex mutex;
-  std::unordered_map<Cache::DeleterFn, CacheEntryRole> role_map;
+  UnorderedMap<Cache::DeleterFn, CacheEntryRole> role_map;
   void Register(Cache::DeleterFn fn, CacheEntryRole role) {
     std::lock_guard<std::mutex> lock(mutex);
     role_map[fn] = role;
   }
-  std::unordered_map<Cache::DeleterFn, CacheEntryRole> Copy() {
+  UnorderedMap<Cache::DeleterFn, CacheEntryRole> Copy() {
     std::lock_guard<std::mutex> lock(mutex);
     return role_map;
   }
@@ -65,7 +65,7 @@ void RegisterCacheDeleterRole(Cache::DeleterFn fn, CacheEntryRole role) {
   GetRegistry().Register(fn, role);
 }
 
-std::unordered_map<Cache::DeleterFn, CacheEntryRole> CopyCacheDeleterRoleMap() {
+UnorderedMap<Cache::DeleterFn, CacheEntryRole> CopyCacheDeleterRoleMap() {
   return GetRegistry().Copy();
 }
 

cache/cache_entry_roles.h

@@ -9,9 +9,9 @@
 #include <cstdint>
 #include <memory>
 #include <type_traits>
-#include <unordered_map>
 
 #include "rocksdb/cache.h"
+#include "util/hash_containers.h"
 
 namespace ROCKSDB_NAMESPACE {
 
@@ -78,7 +78,7 @@ void RegisterCacheDeleterRole(Cache::DeleterFn fn, CacheEntryRole role);
 // * This is suitable for preparing for batch operations, like with
 // CacheEntryStatsCollector.
 // * The number of mappings should be sufficiently small (dozens).
-std::unordered_map<Cache::DeleterFn, CacheEntryRole> CopyCacheDeleterRoleMap();
+UnorderedMap<Cache::DeleterFn, CacheEntryRole> CopyCacheDeleterRoleMap();
 
 // ************************************************************** //
 // An automatic registration infrastructure. This enables code

cache/cache_reservation_manager_test.cc

@@ -47,13 +47,14 @@ TEST_F(CacheReservationManagerTest, GenerateCacheKey) {
 
   // Next unique Cache key
   CacheKey ckey = CacheKey::CreateUniqueForCacheLifetime(cache.get());
-  // Back it up to the one used by CRM (using CacheKey implementation details)
-  using PairU64 = std::pair<uint64_t, uint64_t>;
+  // Get to the underlying values
+  using PairU64 = std::array<uint64_t, 2>;
   auto& ckey_pair = *reinterpret_cast<PairU64*>(&ckey);
-  ckey_pair.second--;
+  // Back it up to the one used by CRM (using CacheKey implementation details)
+  ckey_pair[1]--;
 
   // Specific key (subject to implementation details)
-  EXPECT_EQ(ckey_pair, PairU64(0, 2));
+  EXPECT_EQ(ckey_pair, PairU64({0, 2}));
 
   Cache::Handle* handle = cache->Lookup(ckey.AsSlice());
   EXPECT_NE(handle, nullptr)