mosquitto-users team mailing list archive

[Bart Van Der Meerssche <bart.vandermeerssche@xxxxxxxxxx>]

Hi Andy^2,

My use case includes listening on multiple sockets/pipes/devs 
simultaneously, processing and then passing on the message. mqtt_lua is 
not evented AFAIK. You need to call mqtt_client:handler() every second 
or so, much like mosquitto_loop.

I like the fact that libmosquitto allows loop polling, integration with 
an external event loop and a threaded approach with internal event loop.

Cheers
/Bart


On 12/12/2012 10:43 PM, andypiperuk@xxxxxxxxx wrote:
> You know that the Eclipse Paho project has a Lua client due to hit Git
> within days, right?
>
> On Wednesday, December 12, 2012, Bart Van Der Meerssche wrote:
>
>     Hello list,
>
>     I'm currently writing Lua bindings for libmosquitto [1]. Since Lua
>     does not support preemptive multithreading, using
>     mosquitto_loop_start is not an option. As suggested in the
>     libmosquitto documentation, I'm integrating
>     mosquitto_loop_read/write/misc into a Lua event loop instead. The
>     basic functionality works ok. However, when a network error occurs
>     or the broker shuts down, the event loop starts busy looping. strace
>     output:
>
>     poll([{fd=5, events=POLLIN}, {fd=6, events=POLLIN}], 2, -1) = 1
>     ([{fd=6, revents=POLLIN}])
>     read(6, "", 1)                          = 0
>     poll([{fd=5, events=POLLIN}, {fd=6, events=POLLIN}], 2, -1) = 1
>     ([{fd=6, revents=POLLIN}])
>     read(6, "", 1)                          = 0
>
>     ...
>
>     stracing the libmosquitto event loop:
>     [pid 12721] select(4, [3], [], NULL, {1, 0}) = 1 (in [3], left {0,
>     332713})
>     [pid 12721] read(3, "", 1)              = 0
>     [pid 12721] close(3)                    = 0
>
>     Looking at the mosquitto_loop code shows that if a read or write
>     error occurs, the socket is closed with the private
>     _mosquitto_socket_close function, which updates the internal mosq
>     state as well. This means that the current libmosquitto API doesn't
>     allow a proper implementation in an external event loop. Making
>     _mosquitto_socket_close public would be a start. Integrating the rc
>     handling of:
>     * rc = mosquitto_loop_read(mosq, max_packets)
>     * rc = mosquitto_loop_write(mosq, max_packets)
>     inside these public functions could be an even cleaner approach.
>
>     Would such a code change be an option?
>
>     [1]
>     https://github.com/flukso/__flm02/tree/rfm12/openwrt/__package/lua-mosquitto/src
>     <https://github.com/flukso/flm02/tree/rfm12/openwrt/package/lua-mosquitto/src>
>
>
>     Cheers
>     /Bart
>
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