text: /*
   * Copyright 2017 Facebook, Inc.
   *
   * 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 <folly/Baton.h>
  
  #include <thread>
  
  #include <folly/Benchmark.h>
  #include <folly/portability/GFlags.h>
  #include <folly/portability/GTest.h>
  #include <folly/portability/Semaphore.h>
  #include <folly/test/BatonTestHelpers.h>
  #include <folly/test/DeterministicSchedule.h>
  
  using namespace folly;
  using namespace folly::test;
  using folly::detail::EmulatedFutexAtomic;
  
  typedef DeterministicSchedule DSched;
  
  BENCHMARK(baton_pingpong_single_poster_blocking, iters) {
    run_pingpong_test<std::atomic, true, true>(iters);
  }
  
  BENCHMARK(baton_pingpong_multi_poster_blocking, iters) {
    run_pingpong_test<std::atomic, false, true>(iters);
  }
  
  BENCHMARK(baton_pingpong_single_poster_nonblocking, iters) {
    run_pingpong_test<std::atomic, true, false>(iters);
  }
  
  BENCHMARK(baton_pingpong_multi_poster_nonblocking, iters) {
    run_pingpong_test<std::atomic, false, false>(iters);
  }
  
  BENCHMARK_DRAW_LINE()
  
  BENCHMARK(baton_pingpong_emulated_futex_single_poster_blocking, iters) {
    run_pingpong_test<EmulatedFutexAtomic, true, true>(iters);
  }
  
  BENCHMARK(baton_pingpong_emulated_futex_multi_poster_blocking, iters) {
    run_pingpong_test<EmulatedFutexAtomic, false, true>(iters);
  }
  
  BENCHMARK(baton_pingpong_emulated_futex_single_poster_nonblocking, iters) {
    run_pingpong_test<EmulatedFutexAtomic, true, false>(iters);
  }
  
  BENCHMARK(baton_pingpong_emulated_futex_multi_poster_nonblocking, iters) {
    run_pingpong_test<EmulatedFutexAtomic, false, false>(iters);
  }
  
  BENCHMARK_DRAW_LINE()
  
  BENCHMARK(posix_sem_pingpong, iters) {
    sem_t sems[3];
    sem_t* a = sems + 0;
    sem_t* b = sems + 2; // to get it on a different cache line
  
    sem_init(a, 0, 0);
    sem_init(b, 0, 0);
    auto thr = std::thread([=] {
      for (size_t i = 0; i < iters; ++i) {
        sem_wait(a);
        sem_post(b);
      }
    });
    for (size_t i = 0; i < iters; ++i) {
      sem_post(a);
      sem_wait(b);
    }
    thr.join();
  }
  
  // I am omitting a benchmark result snapshot because these microbenchmarks
  // mainly illustrate that PreBlockAttempts is very effective for rapid
  // handoffs.  The performance of Baton and sem_t is essentially identical
  // to the required futex calls for the blocking case
  
  int main(int argc, char** argv) {
    testing::InitGoogleTest(&argc, argv);
    gflags::ParseCommandLineFlags(&argc, &argv, true);
  
    auto rv = RUN_ALL_TESTS();
    if (!rv && FLAGS_benchmark) {
      folly::runBenchmarks();
    }
    return rv;
  }
  