absl: add Mutex::ReaderLock benchmark

PiperOrigin-RevId: 566961701
Change-Id: Id04e4c5a598f508a0fe7532ae8f084c583865f2d

absl/synchronization/mutex_benchmark.cc

@@ -34,6 +34,14 @@ void BM_Mutex(benchmark::State& state) {
 }
 }
 BENCHMARK(BM_Mutex)->UseRealTime()->Threads(1)->ThreadPerCpu();
 BENCHMARK(BM_Mutex)->UseRealTime()->Threads(1)->ThreadPerCpu();
 
 
+void BM_ReaderLock(benchmark::State& state) {
+  static absl::Mutex* mu = new absl::Mutex;
+  for (auto _ : state) {
+    absl::ReaderMutexLock lock(mu);
+  }
+}
+BENCHMARK(BM_ReaderLock)->UseRealTime()->Threads(1)->ThreadPerCpu();
+
 static void DelayNs(int64_t ns, int* data) {
 static void DelayNs(int64_t ns, int* data) {
   int64_t end = absl::base_internal::CycleClock::Now() +
   int64_t end = absl::base_internal::CycleClock::Now() +
                 ns * absl::base_internal::CycleClock::Frequency() / 1e9;
                 ns * absl::base_internal::CycleClock::Frequency() / 1e9;