lwm2m: use asynchronous socket io
This restructures the lwm2m_engine to use a non-blocking socket access
instead of the previously used blocking style, and eliminates any
socket-access from outside of the main work loop.
The main motivation behind this is an issue within nordics
nrf_modem_lib/modem-fw on nrf9160, that leads to socket send() calls to
block indefinitely when the shared memory used for
rpc-communication with the modem is already exhausted because of
incoming data.
This lead to the lwm2m_engine locking up on send calls when there is
also a large amount of incoming data.
This works around this issue, by only issuing send calls when poll
reports the socket to be ready for sending, and (more importantly) by
always receiving all buffered incoming data before sending anything.
There might still be a (perhaps academic) possibility where this
situation might be triggered, when the scheduler interrupts the lwm2m
thread in-between receiving and sending, but for now we have not yet
observed this.
Besides working around the aforementioned issue, this also simplifies
the way resends are handled as they are no longer send from the main
system-workqueue, and limits all interaction with the sockets to a
single thread.
Signed-off-by: Henning Fleddermann <henning.fleddermann@grandcentrix.net>
6 files changed
