Add context_benchmark. (#213)

Author: g-easy

opencensus/context/BUILD

@@ -61,3 +61,19 @@ cc_test(
         "@com_google_googletest//:gtest_main",
     ],
 )
+
+# Benchmarks
+# ========================================================================= #
+
+cc_binary(
+    name = "context_benchmark",
+    testonly = 1,
+    srcs = ["internal/context_benchmark.cc"],
+    copts = TEST_COPTS,
+    linkopts = ["-pthread"],  # Required for absl/synchronization bits.
+    linkstatic = 1,
+    deps = [
+        ":context",
+        "@com_github_google_benchmark//:benchmark",
+    ],
+)

opencensus/context/internal/context_benchmark.cc

@@ -0,0 +1,55 @@
+// Copyright 2018, OpenCensus Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "opencensus/context/context.h"
+
+#include <functional>
+
+#include "benchmark/benchmark.h"
+
+namespace opencensus {
+namespace context {
+namespace {
+
+void BM_ContextCurrent(benchmark::State& state) {
+  benchmark::DoNotOptimize(Context::Current());  // Force TLS initialization.
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(Context::Current());
+  }
+}
+BENCHMARK(BM_ContextCurrent);
+
+void BM_CopyDefaultContext(benchmark::State& state) {
+  Context ctx = Context::Current();
+  for (auto _ : state) {
+    Context copy = ctx;
+    benchmark::DoNotOptimize(copy);
+  }
+}
+BENCHMARK(BM_CopyDefaultContext);
+
+void BM_WrapDefaultContext(benchmark::State& state) {
+  Context ctx = Context::Current();
+  std::function<void()> fn = []() {};
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(ctx.Wrap(fn));
+  }
+}
+BENCHMARK(BM_WrapDefaultContext);
+
+}  // namespace
+}  // namespace context
+}  // namespace opencensus
+
+BENCHMARK_MAIN();