Function fsync

lib/cpp/test/TFileTransportTest.cpp:147–152

// This returns immediately, so timing in test_destructor() isn't affected by
// waiting on the actual filesystem.
extern "C" int fsync(int fd) {
  if (fsync_log) {
    fsync_log->fsync(fd);
  }
  return 0;
}

int time_diff(const struct timeval* t1, const struct timeval* t2) {
  return (t2->tv_usec - t1->tv_usec) + (t2->tv_sec - t1->tv_sec) * 1000000;