Fix Statistics in db_stress (#9260)

Summary:
The `Statistics` objects are meant to be shared across translation
units, but this was prevented by declaring them static. We need to
ensure they are defined once in the program. The effect is now
`StressTest::PrintStatistics()` can actually print statistics since it
now sees non-null values when `--statistics=1`.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9260

Reviewed By: zhichao-cao

Differential Revision: D32910162

Pulled By: ajkr

fbshipit-source-id: c926d6f556177987bee5fa3cbc87597803b230ee

TARGETS

@@ -871,6 +871,7 @@ cpp_library(
         "db_stress_tool/db_stress_gflags.cc",
         "db_stress_tool/db_stress_listener.cc",
         "db_stress_tool/db_stress_shared_state.cc",
+        "db_stress_tool/db_stress_stat.cc",
         "db_stress_tool/db_stress_test_base.cc",
         "db_stress_tool/db_stress_tool.cc",
         "db_stress_tool/expected_state.cc",

db_stress_tool/CMakeLists.txt

@@ -7,6 +7,7 @@ add_executable(db_stress${ARTIFACT_SUFFIX}
   db_stress_gflags.cc
   db_stress_listener.cc
   db_stress_shared_state.cc
+  db_stress_stat.cc
   db_stress_test_base.cc
   db_stress_tool.cc
   expected_state.cc

db_stress_tool/db_stress_stat.cc

@@ -0,0 +1,17 @@
+//  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).
+
+#ifdef GFLAGS
+
+#include "db_stress_tool/db_stress_stat.h"
+
+namespace ROCKSDB_NAMESPACE {
+
+std::shared_ptr<ROCKSDB_NAMESPACE::Statistics> dbstats;
+std::shared_ptr<ROCKSDB_NAMESPACE::Statistics> dbstats_secondaries;
+
+}  // namespace ROCKSDB_NAMESPACE
+
+#endif  // GFLAGS

db_stress_tool/db_stress_stat.h

@@ -21,9 +21,10 @@ DECLARE_bool(histogram);
 DECLARE_bool(progress_reports);
 
 namespace ROCKSDB_NAMESPACE {
+
 // Database statistics
-static std::shared_ptr<ROCKSDB_NAMESPACE::Statistics> dbstats;
-static std::shared_ptr<ROCKSDB_NAMESPACE::Statistics> dbstats_secondaries;
+extern std::shared_ptr<ROCKSDB_NAMESPACE::Statistics> dbstats;
+extern std::shared_ptr<ROCKSDB_NAMESPACE::Statistics> dbstats_secondaries;
 
 class Stats {
  private:

src.mk

@@ -349,6 +349,7 @@ STRESS_LIB_SOURCES =                                            \
   db_stress_tool/db_stress_gflags.cc                           \
   db_stress_tool/db_stress_listener.cc                         \
   db_stress_tool/db_stress_shared_state.cc                     \
+  db_stress_tool/db_stress_stat.cc                             \
   db_stress_tool/db_stress_test_base.cc                        \
   db_stress_tool/db_stress_tool.cc                             \
   db_stress_tool/expected_state.cc                             \