Allows to get current frames waiting to be sent on the given connection.
This function will iterate over all channels the connection have checking if there are frames pending to be sent. The cumulative result for this iteration will be returned as the pending message to be sent over this connection or session.
This function is actually used by the vortex writer to be able to normalize its pending task to be processed situation while unreferring connections.
|connection ||a connection to know how many message are pending to be sent.|
- the number or message pending to be sent.