ase all processing will be cancelled immediately
      and all resources will be returned to system by recycle() call. Current
      call of dcraw_process() will return error code
      LIBRAW_CANCELLED_BY_CALLBACK.</p>
    <p>Callback parameters:</p>
    <dl>
      <dt>void *callback_data</dt>
      <dd>void*-pointer, passed as 2nd argument to set_progress_handler(). This
        pointer should be used to pass additional data to callback (i.e. thread
        local data and so on).</dd>
      <dt>enum LibRa