On 5/7/19 7:55 AM, Alec Warner wrote: > > > On Mon, May 6, 2019 at 8:15 PM Zac Medico <zmed...@gentoo.org > <mailto:zmed...@gentoo.org>> wrote: > > Add a reentrant lock/unlock method which is useful for things like > emaint binhost and eclean-pkg. The vardbapi class already provides > lock/unlock methods that behave the same way. > > > Curious why we are not doing more encapsulation here. > > I'd suggest a new class type in locks.py: > > class RefCountedLock(object): ... > # This implements the Lock() / Unlock() interface, as well as perhaps > __enter__ and __exit__. > # It uses a lockfile at path and a reference count. > > Then in bintree's init, set self.lock to > locks.refCountedLock(self.bintree._pkgindex_file) > > def lock(self): # on bintree > self._lock.Lock() > > def unlock(self): > self._lock.Unlock()
Yes, splitting out a reference counted lock class like this is a good
idea. I'll do that.
> 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()
--
Thanks,
Zac
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