Method DoRead

be/src/runtime/io/scan-range.cc:295–332

}

ReadOutcome ScanRange::DoRead(DiskQueue* queue, int disk_id) {
  bool use_local_buffer = false;
  bool use_mem_buffer = false;
  if (disk_file_ != nullptr && disk_file_->disk_type() != DiskFileType::LOCAL
      && disk_buffer_file_ != nullptr) {
    // The sequence for acquiring the locks should always be from the local to
    // the remote to avoid deadlocks.
    shared_lock<shared_mutex> local_file_lock(*(disk_buffer_file_->GetFileLock()));
    shared_lock<shared_mutex> remote_file_lock(*(disk_file_->GetFileLock()));
    {
      unique_lock<SpinLock> buffer_file_lock(*(disk_buffer_file_->GetStatusLock()));
      unique_lock<SpinLock> file_lock(*(disk_file_->GetStatusLock()));
      if (disk_buffer_file_->is_deleted(buffer_file_lock)
          && disk_file_->is_deleted(file_lock)) {
        // If both of the local buffer file and the remote file have been deleted,
        // the only case could be the query is cancelled, so that both files are deleted.
        return ReadOutcome::CANCELLED;
      }

      // The range can be read from local for two cases.
      // 1. If the local buffer file is not deleted(evicted) yet.
      // 2. A block of the file, which contains the range, has been read and stored in
      // the memory.
      // If we don't meet any of the cases, the range needs to be read from the remote.
      if (!disk_buffer_file_->is_deleted(buffer_file_lock)) {
        use_local_buffer = true;
      } else if (disk_buffer_file_->CanReadFromReadBuffer(local_file_lock, offset_)) {
        use_mem_buffer = true;
      } else {
        // Read from the remote file. The remote file must be in persisted status.
        DCHECK(disk_file_->is_persisted(file_lock));
      }
    }
    return DoReadInternal(
        queue, disk_id, use_local_buffer, use_mem_buffer, &local_file_lock);
  }
  return DoReadInternal(queue, disk_id, use_local_buffer, use_mem_buffer);
}

Status ScanRange::ReadSubRanges(
    DiskQueue* queue, BufferDescriptor* buffer_desc, bool* eof, FileReader* file_reader) {