Hi Davide,
> > > > > > As I think about this more, I see more problems with
> > > > > > your argument. timerfd needs the ability to get and
> > > > > > get-while-setting just as much as the earlier APIs.
> > > > > > Consider a library that creates a timerfd file descriptor that
> > > > > > is handed off to an application: that library may want
> > > > > > to modify the timer settings without having to create a
> > > > > > new file descriptor (the app mey not be able to be told about
> > > > > > the new fd). Your argument just doesn't hold, AFAICS.
> > > > >
> > > > > Such hypotethical library, in case it really wanted to offer such
> > > > > functionality, could simply return an handle instead of the raw
> > > > > fd, and take care of all that stuff in userspace.
> > > >
> > > > Did I miss something? Is it not the case that as soon as the
> > > > library returns a handle, rather than an fd, then the whole
> > > > advantage of timerfd() (being able to select/poll/epoll on
> > > > the timer as well as other fds) is lost?
> > >
> > > Why? The handle would simply be a little struct where the timerfd fd
> > > is
> > > stored, and a XXX_getfd() would return it.
> > > So my point is, I doubt such functionalities are really needed, and I
> > > also argue that the kernel is the best place for such wrapper code
> > > to go.
> >
> > So what happens if one thread (via the library) wants modify
> > a timer's settings at the same timer as another thread is
> > select()ing on it? The first thread can't do this by creating
> > a new timerfd timer, since it wants to affect the select()
> > in the other thread?
>
> It can be done w/out any problems. The select thread will be notified
> whenever the new timer setting expires.
We are going in circles here. I think you are missing my point.
Consider the following
[[
Thread A: calls library function which creates a timerfd file
descriptor.
Thread B: calls select() on the timerfd file descriptor.
Thread A: calls library function which wants to:
a) modify timer settings, and retrieve copy of current timer
settings, and later
b) restore old timer settings.
]]
This seems a quite reasonable use-case to me, and the existing
interface simply can't support it.
Cheers,
Michael
--
Michael Kerrisk
maintainer of Linux man pages Sections 2, 3, 4, 5, and 7
Want to help with man page maintenance?
Grab the latest tarball at
http://www.kernel.org/pub/linux/docs/manpages ,
read the HOWTOHELP file and grep the source
files for 'FIXME'.
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