On Sa, 07.01.23 10:35, Stanislav Angelovič (stanislav.angelo...@protonmail.com) wrote:
> Hi everyone, > > According to sd_bus_get_timeout(3) man page, sd_bus_get_timeout() > returns "timeout in us to pass to poll()" and it also states that > "the returned time-value is relative". > > However, in reality, this function returns an absolute time point > (a-ka relative to the monotonic clock epoch). Hence, the returned > value cannot be simply converted to milliseconds and given to > poll(). It must first be subtracted from the current monotonic clock > time. > > I followed the documentation and had a bug in my code for some time > :) Shall the documentation be updated to mention the necessity of > conversion from absolute to relative? Or does sd_bus_get_timeout() > have a bug and shall this function do the subtraction for the user > and return relative time? Hmm, the man page says this currently: https://www.freedesktop.org/software/systemd/man/sd_bus_get_fd.html#Description Note that the returned time-value is absolute, based of CLOCK_MONOTONIC and specified in microseconds. When converting this value in order to pass it as third argument to poll() (which expects relative milliseconds), care should be taken to convert to a relative time and use a division that rounds up to ensure the I/O polling operation doesn't sleep for shorter than necessary, which might result in unintended busy looping (alternatively, use ppoll(2) instead of plain poll(), which understands timeouts with nano-second granularity). That's pretty explicit already, no? (I mean, you have half a point, the first sentence of the explanation might people think this was a relative timeout, but we all read the full documentation, no, before actually using this API, no? ;-)) Anyway, will prep a fix that rewords the first sentence to make this clearer right away. Lennart -- Lennart Poettering, Berlin
