[systemd-devel] sd_bus_process() - ECONNRESET due to bus timeout?

[Al Chu]

Hi,

I have a bit of a code that loosely does the following:

- setup a "org.freedesktop.DBus.Properties" / "PropertiesChanged"
callback via `sd_bus_match_signal_async()`

- through a file descriptor event reactor, watch the file descriptor
returned by `sd_bus_get_fd()`.

- when I see file descriptor activity, call `sd_bus_process()` in a
loop as described in the manpage.

- in the callback determine if the process has exited, check exit code,
etc. and handle as needed.

I've noticed that my code works fine for a process that runs < ~25
seconds, but for tasks that run longer than 25 seconds,
`sd_bus_process()` returns ECONNRESET.

I can't help but wonder if the default BUS_DEFAULT_TIMEOUT of 25
seconds is in play here.  I'm on Centos 8 which is at systemd v239,
which unfortunately does not seem to support SYSTEMD_BUS_TIMEOUT or
`sd_bus_set_method_call_timeout()` (AFAICT v240 is when they were
added).

I'm wondering if I'm just missing some subtlety on how to get this to
work.

- Am I simply required to re-establish the connection when I get
ECONNRESET?  I thought this possible, but 25 seconds seems somewhat
short and callers would just regularly miss changes they want to see.

- Is there some "keepalive" NOOP to be done?

- Is the bus timeout affecting me and I will have to use a newer
systemd version?

Thanks,

Al

-- 
Albert Chu
chu11 at llnl.gov
Computer Scientist
High Performance Systems Division
Lawrence Livermore National Laboratory