Libcanard listing active CanardRxSubscription

PetervdPerk · May 20, 2021, 9:14am

Currently you’ve to keep a seperate list of the active CanardRxSubscription to be able to print information e.g. active portIds of all active subscribers. Although technically this information is already available in libcanard.

Would it be something to expose the list of active CanardRxSubscriptions from libcanard so we could easily print status information?

pavel.kirienko · May 20, 2021, 9:16am

This information is already exposed, although the API might be considered a bit quirky:

github.com

UAVCAN/demos/blob/bfdbae036bab4cd389f567127fbd7640021c7e28/ds015_servo/src/main.c#L455-L460


rxs = state->canard._rx_subscriptions[CanardTransferKindRequest];
while (rxs != NULL)
{
    nunavutSetBit(&m.servers.mask_bitpacked_[0], sizeof(m.servers.mask_bitpacked_), rxs->_port_id, true);
    rxs = rxs->_next;
}

Should we improve it?

PetervdPerk · May 20, 2021, 9:22am

github.com

UAVCAN/libcanard/blob/master/libcanard/canard.h#L350


    /// They SHALL be valid function pointers at all times.
    /// The time complexity models given in the API documentation are made on the assumption that the memory management
    /// functions have constant complexity O(1).
    ///
    /// The following API functions may allocate memory:   canardRxAccept(), canardTxPush().
    /// The following API functions may deallocate memory: canardRxAccept(), canardRxSubscribe(), canardRxUnsubscribe().
    /// The exact memory requirement and usage model is specified for each function in its documentation.
    CanardMemoryAllocate memory_allocate;
    CanardMemoryFree     memory_free;
    /// These fields are for internal use only. Do not access from the application.
    CanardRxSubscription*             _rx_subscriptions[CANARD_NUM_TRANSFER_KINDS];
    struct CanardInternalTxQueueItem* _tx_queue;
};
/// Construct a new library instance.
/// The default values will be assigned as specified in the structure field documentation.
/// If any of the pointers are NULL, the behavior is undefined.
///
/// The instance does not hold any resources itself except for the allocated memory.
/// If the instance should be de-initialized, the application shall clear the TX queue by calling the pop function

Well currently it’s stated it’s for internal use only, thus you expect the API can be unstable.
Maybe adding an access function would be nice and futureproof.

pavel.kirienko · May 20, 2021, 9:24am

How about we just remove the leading underscore and update the docs to state “do not modify this” instead of “internal use only”? Adding an extra accessor would go against the spirit of libcanard, I think.

PetervdPerk · May 20, 2021, 9:25am

Yes that will do

pavel.kirienko · May 20, 2021, 9:33am

I won’t be able to work on this soon, but a pull request would be accepted!