Method GetOrCreateSubStream

tensorflow/stream_executor/stream.cc:2528–2573

}

Stream *Stream::GetOrCreateSubStream() {
  absl::MutexLock lock(&mu_);

  // Look for the first reusable sub_stream that is ok, dropping !ok sub_streams
  // we encounter along the way.
  for (int64 index = 0; index < sub_streams_.size();) {
    std::pair<std::unique_ptr<Stream>, bool> &pair = sub_streams_[index];
    if (pair.second) {
      // The sub_stream is reusable.
      Stream *sub_stream = pair.first.get();
      if (sub_stream->ok()) {
        VLOG(1) << DebugStreamPointers() << " reusing sub_stream "
                << sub_stream->DebugStreamPointers();
        pair.second = false;
        return sub_stream;
      }

      // The stream is reusable and not ok. Streams have a monotonic state
      // machine; the stream will remain in !ok forever. Swap it with the last
      // stream and pop it off.
      const int64 last = sub_streams_.size() - 1;
      if (index != last) {
        std::swap(pair, sub_streams_[last]);
      }
      sub_streams_.pop_back();
      VLOG(1) << DebugStreamPointers() << " dropped !ok sub_stream "
              << sub_stream->DebugStreamPointers();
    } else {
      // The sub_stream is not reusable, move on to the next one.
      ++index;
    }
  }

  // No streams are reusable; create a new stream.
  sub_streams_.emplace_back(std::unique_ptr<Stream>{new Stream{parent_}},
                            false);
  Stream *sub_stream = sub_streams_.back().first.get();
  sub_stream->Init();
  if (!sub_stream->ok_) {
    LOG(ERROR) << "sub-stream failed to be initialized";
  }
  VLOG(1) << DebugStreamPointers() << " created new sub_stream "
          << sub_stream->DebugStreamPointers();

  return sub_stream;
}

void Stream::ReturnSubStream(Stream *sub_stream) {
  absl::MutexLock lock(&mu_);