Refactor threading run (#1961)

* ThreadManager::WaitForAllThreads removed

* WaitForAllThreads was only called either in single threaded
  environments or just before all threads are joined anyway. As this
  doesn't add a useful synchronization point, it's removed.

* Formatting issue

* Thread Sanitizer satisfied

* More formatting issues

Author: krzikalla

src/benchmark_runner.cc

@@ -302,7 +302,6 @@ BenchmarkRunner::IterationResults BenchmarkRunner::DoNIterations() {
               /*profiler_manager=*/nullptr);
 
   // The main thread has finished. Now let's wait for the other threads.
-  manager->WaitForAllThreads();
   for (std::thread& thread : pool) {
     thread.join();
   }
@@ -434,7 +433,6 @@ MemoryManager::Result BenchmarkRunner::RunMemoryManager(
   RunInThread(&b, memory_iterations, 0, manager.get(),
               perf_counters_measurement_ptr,
               /*profiler_manager=*/nullptr);
-  manager->WaitForAllThreads();
   manager.reset();
   b.Teardown();
   MemoryManager::Result memory_result;
@@ -450,7 +448,6 @@ void BenchmarkRunner::RunProfilerManager(IterationCount profile_iterations) {
   RunInThread(&b, profile_iterations, 0, manager.get(),
               /*perf_counters_measurement_ptr=*/nullptr,
               /*profiler_manager=*/profiler_manager);
-  manager->WaitForAllThreads();
   manager.reset();
   b.Teardown();
 }

src/thread_manager.h

@@ -11,30 +11,15 @@ namespace internal {
 
 class ThreadManager {
  public:
-  explicit ThreadManager(int num_threads)
-      : alive_threads_(num_threads), start_stop_barrier_(num_threads) {}
+  explicit ThreadManager(int num_threads) : start_stop_barrier_(num_threads) {}
 
   Mutex& GetBenchmarkMutex() const RETURN_CAPABILITY(benchmark_mutex_) {
     return benchmark_mutex_;
   }
 
-  bool StartStopBarrier() EXCLUDES(end_cond_mutex_) {
-    return start_stop_barrier_.wait();
-  }
-
-  void NotifyThreadComplete() EXCLUDES(end_cond_mutex_) {
-    start_stop_barrier_.removeThread();
-    if (--alive_threads_ == 0) {
-      MutexLock lock(end_cond_mutex_);
-      end_condition_.notify_all();
-    }
-  }
+  bool StartStopBarrier() { return start_stop_barrier_.wait(); }
 
-  void WaitForAllThreads() EXCLUDES(end_cond_mutex_) {
-    MutexLock lock(end_cond_mutex_);
-    end_condition_.wait(lock.native_handle(),
-                        [this]() { return alive_threads_ == 0; });
-  }
+  void NotifyThreadComplete() { start_stop_barrier_.removeThread(); }
 
   struct Result {
     IterationCount iterations = 0;
@@ -51,10 +36,7 @@ class ThreadManager {
 
  private:
   mutable Mutex benchmark_mutex_;
-  std::atomic<int> alive_threads_;
   Barrier start_stop_barrier_;
-  Mutex end_cond_mutex_;
-  Condition end_condition_;
 };
 
 }  // namespace internal