Re: [gentoo-portage-dev] [PATCH] bindbapi: add reentrant lock method (bug 685236)

[Alec Warner]

On Wed, May 8, 2019 at 2:05 PM Zac Medico <zmedico@g.o> wrote:

> On 5/7/19 1:01 PM, Zac Medico wrote:
> > On 5/7/19 7:55 AM, Alec Warner wrote:
> >
> >> Also curious why we are not implementing enter and exit so we can avoid
> >> unbalanced pairs by using context managers.
> >>
> >> e.g. in match(), we could likely write:
> >>
> >> with self.dbapi.lock():
> >>   # try to match
> >>   update_pkgindex = self._populate_local()
> >>   if update_pkgindex:
> >>     self._pkgindex_write(update_pkgindex)
> >>
> >> If the block raises an exception, __exit__ is still called, so we can
> >> eliminate the finally: blocks and replace them with a careful __exit__
> >> implementation?
> >>
> >> -A
> >
> > Yeah, the reference counted lock class could have a method that returns
> > a context manager which increments/decrements the lock count. The
> > context manager can be implemented with the contextlib.contextmanager
> > decorator like this:
> >
> > @contextlib.contextmanager
> > def contextmanager(self):
> >     self.lock()
> >     try:
> >         yield self
> >     finally:
> >         self.unlock()
> >
>
> Since we really don't want asynchronous code to block waiting for a
> lock, we really should use a (python3.5+ only) asynchronous context
> manager:
>
>
> https://www.python.org/dev/peps/pep-0492/#asynchronous-context-managers-and-async-with
>
> Given that python2.7 is scheduled for retirement in 2020
> (https://pythonclock.org/), maybe it's time to drop support for
> python3.4 and earlier.
>

I haven't used that stuff yet, so I will defer to you on its use; same with
python support.

-A


> --
> Thanks,
> Zac
>
>