Disable IOStatsContext/PerfContext if no thread local (#8117)

Summary:
Before this PR, `get_iostats_context()` will silently return a nullptr if no thread_local support is detected.
This can be the result of build_detect_platform's failure to compile the simple code snippet on certain platforms, as
reported in https://github.com/facebook/mysql-5.6/issues/904.
To be safe, we should fail the compilation if user does not opt out IOStatsContext and
ROCKSDB_SUPPORT_THREAD_LOCAL is not defined.

If RocksDB relies on c++11, can we just always use thread_local? It turns out there might be
performance concerns (https://github.com/facebook/rocksdb/issues/5774),
which is beyond the scope of this PR. We can revisit this later. Here, we stick to the original impl.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/8117

Reviewed By: ajkr

Differential Revision: D27356847

Pulled By: riversand963

fbshipit-source-id: f7d5776842277598d8341b955febb601946801ae

CMakeLists.txt

@@ -326,12 +326,23 @@ CHECK_CXX_SOURCE_COMPILES("
 #endif
 int main() {
   static __thread int tls;
+  (void)tls;
 }
 " HAVE_THREAD_LOCAL)
 if(HAVE_THREAD_LOCAL)
   add_definitions(-DROCKSDB_SUPPORT_THREAD_LOCAL)
 endif()
 
+option(WITH_IOSTATS_CONTEXT "Enable IO stats context" ON)
+if (NOT WITH_IOSTATS_CONTEXT)
+  add_definitions(-DNIOSTATS_CONTEXT)
+endif()
+
+option(WITH_PERF_CONTEXT "Enable perf context" ON)
+if (NOT WITH_PERF_CONTEXT)
+  add_definitions(-DNPERF_CONTEXT)
+endif()
+
 option(FAIL_ON_WARNINGS "Treat compile warnings as errors" ON)
 if(FAIL_ON_WARNINGS)
   if(MSVC)

HISTORY.md

@@ -4,6 +4,7 @@
 * `ColumnFamilyOptions::sample_for_compression` now takes effect for creation of all block-based tables. Previously it only took effect for block-based tables created by flush.
 * `CompactFiles()` can no longer compact files from lower level to up level, which has the risk to corrupt DB (details: #8063). The validation is also added to all compactions.
 * Fixed some cases in which DB::OpenForReadOnly() could write to the filesystem. If you want a Logger with a read-only DB, you must now set DBOptions::info_log yourself, such as using CreateLoggerFromOptions().
+* get_iostats_context() will never return nullptr. If thread-local support is not available, and user does not opt-out iostats context, then compilation will fail. The same applies to perf context as well.
 
 ### Bug Fixes
 * Use thread-safe `strerror_r()` to get error messages.

include/rocksdb/iostats_context.h

@@ -50,7 +50,15 @@ struct IOStatsContext {
   uint64_t cpu_read_nanos;
 };
 
-// Get Thread-local IOStatsContext object pointer
+// If RocksDB is compiled with -DNIOSTATS_CONTEXT, then a pointer to a global,
+// non-thread-local IOStatsContext object will be returned. Attempts to update
+// this object will be ignored, and reading from it will also be no-op.
+// Otherwise,
+// a) if thread-local is supported on the platform, then a pointer to
+//    a thread-local IOStatsContext object will be returned.
+// b) if thread-local is NOT supported, then compilation will fail.
+//
+// This function never returns nullptr.
 IOStatsContext* get_iostats_context();
 
 }  // namespace ROCKSDB_NAMESPACE

include/rocksdb/perf_context.h

@@ -230,8 +230,15 @@ struct PerfContext {
   bool per_level_perf_context_enabled = false;
 };
 
-// Get Thread-local PerfContext object pointer
+// If RocksDB is compiled with -DNPERF_CONTEXT, then a pointer to a global,
-// if defined(NPERF_CONTEXT), then the pointer is not thread-local
+// non-thread-local PerfContext object will be returned. Attempts to update
+// this object will be ignored, and reading from it will also be no-op.
+// Otherwise,
+// a) if thread-local is supported on the platform, then a pointer to
+//    a thread-local PerfContext object will be returned.
+// b) if thread-local is NOT supported, then compilation will fail.
+//
+// This function never returns nullptr.
 PerfContext* get_perf_context();
 
 }  // namespace ROCKSDB_NAMESPACE

monitoring/iostats_context.cc

@@ -9,19 +9,23 @@
 
 namespace ROCKSDB_NAMESPACE {
 
-#ifdef ROCKSDB_SUPPORT_THREAD_LOCAL
+#ifdef NIOSTATS_CONTEXT
+// Should not be used because the counters are not thread-safe.
+// Put here just to make get_iostats_context() simple without ifdef.
+static IOStatsContext iostats_context;
+#elif defined(ROCKSDB_SUPPORT_THREAD_LOCAL)
 __thread IOStatsContext iostats_context;
+#else
+#error \
+    "No thread-local support. Disable iostats context with -DNIOSTATS_CONTEXT."
 #endif
 
 IOStatsContext* get_iostats_context() {
-#ifdef ROCKSDB_SUPPORT_THREAD_LOCAL
   return &iostats_context;
-#else
-  return nullptr;
-#endif
 }
 
 void IOStatsContext::Reset() {
+#ifndef NIOSTATS_CONTEXT
   thread_pool_id = Env::Priority::TOTAL;
   bytes_read = 0;
   bytes_written = 0;
@@ -35,6 +39,7 @@ void IOStatsContext::Reset() {
   logger_nanos = 0;
   cpu_write_nanos = 0;
   cpu_read_nanos = 0;
+#endif  //! NIOSTATS_CONTEXT
 }
 
 #define IOSTATS_CONTEXT_OUTPUT(counter)         \
@@ -43,6 +48,10 @@ void IOStatsContext::Reset() {
   }
 
 std::string IOStatsContext::ToString(bool exclude_zero_counters) const {
+#ifdef NIOSTATS_CONTEXT
+  (void)exclude_zero_counters;
+  return "";
+#else
   std::ostringstream ss;
   IOSTATS_CONTEXT_OUTPUT(thread_pool_id);
   IOSTATS_CONTEXT_OUTPUT(bytes_read);
@@ -61,6 +70,7 @@ std::string IOStatsContext::ToString(bool exclude_zero_counters) const {
   std::string str = ss.str();
   str.erase(str.find_last_not_of(", ") + 1);
   return str;
+#endif  //! NIOSTATS_CONTEXT
 }
 
 }  // namespace ROCKSDB_NAMESPACE

monitoring/iostats_context_imp.h

@@ -7,7 +7,7 @@
 #include "monitoring/perf_step_timer.h"
 #include "rocksdb/iostats_context.h"
 
-#ifdef ROCKSDB_SUPPORT_THREAD_LOCAL
+#if defined(ROCKSDB_SUPPORT_THREAD_LOCAL) && !defined(NIOSTATS_CONTEXT)
 namespace ROCKSDB_NAMESPACE {
 extern __thread IOStatsContext iostats_context;
 }  // namespace ROCKSDB_NAMESPACE
@@ -44,7 +44,7 @@ extern __thread IOStatsContext iostats_context;
       PerfLevel::kEnableTimeAndCPUTimeExceptForMutex); \
   iostats_step_timer_##metric.Start();
 
-#else  // ROCKSDB_SUPPORT_THREAD_LOCAL
+#else  // ROCKSDB_SUPPORT_THREAD_LOCAL && !NIOSTATS_CONTEXT
 
 #define IOSTATS_ADD(metric, value)
 #define IOSTATS_ADD_IF_POSITIVE(metric, value)
@@ -57,4 +57,4 @@ extern __thread IOStatsContext iostats_context;
 #define IOSTATS_TIMER_GUARD(metric)
 #define IOSTATS_CPU_TIMER_GUARD(metric, clock) static_cast<void>(clock)
 
-#endif  // ROCKSDB_SUPPORT_THREAD_LOCAL
+#endif  // ROCKSDB_SUPPORT_THREAD_LOCAL && !NIOSTATS_CONTEXT

monitoring/perf_context.cc

@@ -9,26 +9,22 @@
 
 namespace ROCKSDB_NAMESPACE {
 
-#if defined(NPERF_CONTEXT) || !defined(ROCKSDB_SUPPORT_THREAD_LOCAL)
+#if defined(NPERF_CONTEXT)
+// Should not be used because the counters are not thread-safe.
+// Put here just to make get_perf_context() simple without ifdef.
 PerfContext perf_context;
-#else
+#elif defined(ROCKSDB_SUPPORT_THREAD_LOCAL)
 #if defined(OS_SOLARIS)
-__thread PerfContext perf_context_;
+__thread PerfContext perf_context;
-#else
+#else   // OS_SOLARIS
 thread_local PerfContext perf_context;
-#endif
+#endif  // OS_SOLARIS
+#else
+#error "No thread-local support. Disable perf context with -DNPERF_CONTEXT."
 #endif
 
 PerfContext* get_perf_context() {
-#if defined(NPERF_CONTEXT) || !defined(ROCKSDB_SUPPORT_THREAD_LOCAL)
-  return &perf_context;
-#else
-#if defined(OS_SOLARIS)
-  return &perf_context_;
-#else
   return &perf_context;
-#endif
-#endif
 }
 
 PerfContext::~PerfContext() {