Adding Google benchmarking library.

third_party/google_benchmark/src/mutex.h

Index: third_party/google_benchmark/src/mutex.h
diff --git a/third_party/google_benchmark/src/mutex.h b/third_party/google_benchmark/src/mutex.h
new file mode 100644
index 0000000000000000000000000000000000000000..5f461d05a0c64781bcd08ce380e6cfce1ecab3ad
--- /dev/null
+++ b/third_party/google_benchmark/src/mutex.h
@@ -0,0 +1,155 @@
+#ifndef BENCHMARK_MUTEX_H_
+#define BENCHMARK_MUTEX_H_
+
+#include <condition_variable>
+#include <mutex>
+
+#include "check.h"
+
+// Enable thread safety attributes only with clang.
+// The attributes can be safely erased when compiling with other compilers.
+#if defined(HAVE_THREAD_SAFETY_ATTRIBUTES)
+#define THREAD_ANNOTATION_ATTRIBUTE__(x) __attribute__((x))
+#else
+#define THREAD_ANNOTATION_ATTRIBUTE__(x)  // no-op
+#endif
+
+#define CAPABILITY(x) THREAD_ANNOTATION_ATTRIBUTE__(capability(x))
+
+#define SCOPED_CAPABILITY THREAD_ANNOTATION_ATTRIBUTE__(scoped_lockable)
+
+#define GUARDED_BY(x) THREAD_ANNOTATION_ATTRIBUTE__(guarded_by(x))
+
+#define PT_GUARDED_BY(x) THREAD_ANNOTATION_ATTRIBUTE__(pt_guarded_by(x))
+
+#define ACQUIRED_BEFORE(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(acquired_before(__VA_ARGS__))
+
+#define ACQUIRED_AFTER(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(acquired_after(__VA_ARGS__))
+
+#define REQUIRES(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(requires_capability(__VA_ARGS__))
+
+#define REQUIRES_SHARED(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(requires_shared_capability(__VA_ARGS__))
+
+#define ACQUIRE(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(acquire_capability(__VA_ARGS__))
+
+#define ACQUIRE_SHARED(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(acquire_shared_capability(__VA_ARGS__))
+
+#define RELEASE(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(release_capability(__VA_ARGS__))
+
+#define RELEASE_SHARED(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(release_shared_capability(__VA_ARGS__))
+
+#define TRY_ACQUIRE(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(try_acquire_capability(__VA_ARGS__))
+
+#define TRY_ACQUIRE_SHARED(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(try_acquire_shared_capability(__VA_ARGS__))
+
+#define EXCLUDES(...) THREAD_ANNOTATION_ATTRIBUTE__(locks_excluded(__VA_ARGS__))
+
+#define ASSERT_CAPABILITY(x) THREAD_ANNOTATION_ATTRIBUTE__(assert_capability(x))
+
+#define ASSERT_SHARED_CAPABILITY(x) \
+  THREAD_ANNOTATION_ATTRIBUTE__(assert_shared_capability(x))
+
+#define RETURN_CAPABILITY(x) THREAD_ANNOTATION_ATTRIBUTE__(lock_returned(x))
+
+#define NO_THREAD_SAFETY_ANALYSIS \
+  THREAD_ANNOTATION_ATTRIBUTE__(no_thread_safety_analysis)
+
+namespace benchmark {
+
+typedef std::condition_variable Condition;
+
+// NOTE: Wrappers for std::mutex and std::unique_lock are provided so that
+// we can annotate them with thread safety attributes and use the
+// -Wthread-safety warning with clang. The standard library types cannot be
+// used directly because they do not provided the required annotations.
+class CAPABILITY("mutex") Mutex {
+ public:
+  Mutex() {}
+
+  void lock() ACQUIRE() { mut_.lock(); }
+  void unlock() RELEASE() { mut_.unlock(); }
+  std::mutex& native_handle() { return mut_; }
+
+ private:
+  std::mutex mut_;
+};
+
+class SCOPED_CAPABILITY MutexLock {
+  typedef std::unique_lock<std::mutex> MutexLockImp;
+
+ public:
+  MutexLock(Mutex& m) ACQUIRE(m) : ml_(m.native_handle()) {}
+  ~MutexLock() RELEASE() {}
+  MutexLockImp& native_handle() { return ml_; }
+
+ private:
+  MutexLockImp ml_;
+};
+
+class Barrier {
+ public:
+  Barrier(int num_threads) : running_threads_(num_threads) {}
+
+  // Called by each thread
+  bool wait() EXCLUDES(lock_) {
+    bool last_thread = false;
+    {
+      MutexLock ml(lock_);
+      last_thread = createBarrier(ml);
+    }
+    if (last_thread) phase_condition_.notify_all();
+    return last_thread;
+  }
+
+  void removeThread() EXCLUDES(lock_) {
+    MutexLock ml(lock_);
+    --running_threads_;
+    if (entered_ != 0) phase_condition_.notify_all();
+  }
+
+ private:
+  Mutex lock_;
+  Condition phase_condition_;
+  int running_threads_;
+
+  // State for barrier management
+  int phase_number_ = 0;
+  int entered_ = 0;  // Number of threads that have entered this barrier
+
+  // Enter the barrier and wait until all other threads have also
+  // entered the barrier.  Returns iff this is the last thread to
+  // enter the barrier.
+  bool createBarrier(MutexLock& ml) REQUIRES(lock_) {
+    CHECK_LT(entered_, running_threads_);
+    entered_++;
+    if (entered_ < running_threads_) {
+      // Wait for all threads to enter
+      int phase_number_cp = phase_number_;
+      auto cb = [this, phase_number_cp]() {
+        return this->phase_number_ > phase_number_cp ||
+               entered_ == running_threads_;  // A thread has aborted in error
+      };
+      phase_condition_.wait(ml.native_handle(), cb);
+      if (phase_number_ > phase_number_cp) return false;
+      // else (running_threads_ == entered_) and we are the last thread.
+    }
+    // Last thread has reached the barrier
+    phase_number_++;
+    entered_ = 0;
+    return true;
+  }
+};
+
+}  // end namespace benchmark
+
+#endif  // BENCHMARK_MUTEX_H_