Use known context to close/open stream, question and possible change in v3.1 onward

[walkiry]

Hi, I am considering using the library, however, I am spotting some design choices that I do not understand regarding the open/close packet.

As I understand the packets are closed by the function when the barectf engine is call the callbacks. I understand why you let the user call the function that actually closes the stream's packet.

However, I do not understand why would you use a stream's specific function ( e.g barectf_my_stream_close_packet) rather than a generic function to allow an easy re-usability (e.g close_stream_packet(ctx)). The context holds all the information necessary for this to be possible.

And even better. To allow the same trace to share the callbacks, why not create a barectf ctx and attach all the different streams to it? So we could gain even more re-usability.

[eepp]

Hi there!

A packet closing function is stream-type-specific because it handles stream-type-specific features.

For example, consider this configuration:

%YAML 1.2
--- !<tag:barectf.org,2020/3/config>
trace:
  type:
    native-byte-order: little-endian
    $include:
      - stdint.yaml
    clock-types:
      clk: {}
    data-stream-types:
      A:
        $default-clock-type-name: clk
        event-record-types:
          evt:
            payload-field-type:
              class: structure
              members:
                - val: uint32
      B:
        $features:
          packet:
            discarded-event-records-counter-snapshot-field-type: false
        event-record-types:
          evt:
            payload-field-type:
              class: structure
              members:
                - val: uint32

In the generated barectf.c file, the packet closing functions are different, that is:

• barectf_A_close_packet() gets a value from the user-defined clock value callback and needs the cur_last_event_ts and off_pc_timestamp_end fields of struct barectf_A_ctx (both don't exist in struct barectf_B_ctx).
• barectf_A_close_packet() also needs the off_pc_events_discarded field of struct barectf_A_ctx to know where to write the discarded event record counter snapshot value within the packet context.

Therefore you need to call barectf_A_close_packet() when closing a packet of a data stream of type A and barectf_B_close_packet() when closing a packet of a data stream of type B.

For two data stream types having a default clock type and the exact same features, however, I get your point: barectf could generate a single pair of opening/closing functions for them. Maybe we could define a named class of data stream types in the configuration and link data stream types to this class. Something like this. The tool is just not there yet!