Message and sequence size limited to 4 KiB in protocol sessions

[treiher]

For each message or sequence variable in a session specification, 4 KiB are allocated, independent of the actual type. Larger messages or sequences are not yet supported.

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Tasks

• Enable configuration of buffer sizes using integration file
• Add inference of buffer size for statement-local buffers
• Enable use of separate directory for integration files
• Add documentation

[treiher]

The buffer sizes of message and sequence variables could be made generic parameters of the generated session package. To avoid too many parameters during instantiation, a default value could be predefined. The default value could be settable in the RecordFlux CLI. Custom buffer sizes should be considered in the design of the memory allocator in #629.

[treiher]

Copy of the proposal discussed in #629:

Configuration

Regarding the configuration of memory sizes, we decided to separate those integration aspects into an independent file. For every specification there can be an .rfi (RecordFlux Integration) file which (for now) defines the minimum sizes of all memory regions. For easy human and machine readability we settled on YAML as the format. As there may be multiple such sets of files (e.g. for different system architectures), we'll add a switch to rflx to specify a search path.

The file format looks like this:

Buffer_Size:
    Default: <default_minimum_size>
    Global:
        Global_Variable_1_Name: <minimum_size>
        ...
        Glocal_Variable_n_Name: <minimum_size>
    Local:
        State_1:
            Local_Variable_1_Name: <minimum_size>
            ...
            Local_Variable_n_Name: <minimum_size>
        ...
        State_m:
            Local_Variable_1_Name: <minimum_size>
            ...
            Local_Variable_n_Name: <minimum_size>

The default size is used for all memory regions for which no explicit size is specified.

Calculation

Calculation of the required buffer sizes should be simple. The number of required buffers obviously is the maximum number of local variables used in any state. For every state we sort the required variable sizes in descending order and extend the resulting list to have the maximum length (by adding 0 size values). To calculate the required slot sizes, we simply take the maximum value for every position in every list across all states. The allocation for a local variable in a state simply is the position in the (state-specific) list referring to that local variable.

[kanigsson]

Are multiple sessions in a single .rflx file supported? If yes, we need to specify the session name in the corresponding .rfi file.

[treiher]

Yes, you are right. A specification file can contain multiple sessions, and we need to differentiate them in the .rfi file. We could adapt the proposed file format as follows:

Session_1_Name:
    Buffer_Size:
        Default: <default_minimum_size>
        Global:
            Global_Variable_1_Name: <minimum_size>
            ...
Session_2_Name:
    Buffer_Size:
        Default: <default_minimum_size>
        Global:
            Global_Variable_1_Name: <minimum_size>
            ...

[kanigsson]

Do we want to keep the file open for other uses, including not related to sessions? In that case, it could be better to have a top-level entry for the Buffer_Size stuff, something like that maybe:

Buffer_Size:
    Session_1_Name:
        Default: <default_minimum_size>
        Global:
            Global_Variable_1_Name: <minimum_size>
            ...
    Session_2_Name:
        Default: <default_minimum_size>
        Global:
            Global_Variable_1_Name: <minimum_size>
            ...

Another question: Do we want to allow default values per state, or globally per session only?

[treiher]

You are right, we should keep the file format extendable. I have discussed that with @senier, and we came up with the following format:

Session:
    Session_1_Name:
        Buffer_Size:
            Default: <default_minimum_size>
            Global:
                Global_Variable_1_Name: <minimum_size>
                ...
    Session_2_Name:
        Buffer_Size:
            Default: <default_minimum_size>
            Global:
                Global_Variable_1_Name: <minimum_size>
                ...

This format also makes it easier to add further configuration options to a session which are not related to buffer sizes.

[kanigsson]

I can't add tasks to this issue given that the first post was by Tobias. Tobias, can you please add the item "Documentation" to the task list?

[treiher]

Sure, I have added it.

[kanigsson]

I think this can be closed now. Any other items that anybody can think of?

[treiher]

As all tasks are completed and merged, this issue can be closed.