[systemd-devel] Fwd: sdbus-filedescriptor does reproducibly NOT get triggered in a specific situation

[Jan Mueller]

> > I have the following issue:

> > An application does not receive dbus signals on its dbus file
descriptor *while waiting* for a

> > dbus-method response. Considered time frame: between sending the
method-call and receiving

> > its response. After the response is being received, the (indefinitely)
queued signal is not delivered

> > until another signal / method call triggers the sdbus file descriptor
(which is supervised by

> > select()/epoll()).

> Don't use select() anymore. It's inefficient and can't handle fds >

> > 1024. Use poll() or epoll(). (I'll prep a patch now that removes any

> > mention of select() from our man pages, as we shouldn't mislead users

> > to ever use it.)

>
> Morever, when waiting on a bus object you need to use the fd returned

> > by sd_bus_get_fd() and wait for the events returned by
> sd_bus_get_events() (which are POLLIN/POLLOUT/… events). Yes this

> > could benefit from documentation. The timeout passed to poll() should

> > be the one returned by sd_bus_get_timeout() or shorter.

>
> Whenever poll() reports anything call sd_bus_process(), which will do

> > the work.

>
> Lennart

>
Hey Lennart - thank you for the quick response!
Ok, originally I stripped it down to select() for better comprehension.
Swichting back to epoll + making use of sd_bus_get_events() did not help
receiving the signals in this very situation. The basic communication
between
sender and receiver works fine so far though. I did already make use of
sd_bus_get_fd() and sd_bus_process() - please see the referenced +
updated example project:
https://github.com/mue-jan/dbus-missing-signals-or-fd-issue

By the way: sd_bus_get_events() returns "0" in the referenced code-example.
The function-result printing is located right before the while(1) loop
around
epoll.

Jan
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