[PATCH] repair: use context manager for lock management

[Gregory Szorc]

On Sun, Mar 26, 2017 at 4:20 AM, Yuya Nishihara <yuya at tcha.org> wrote:

> On Fri, 24 Mar 2017 23:34:28 -0400, Matt Harbison wrote:
> > # HG changeset patch
> > # User Matt Harbison <matt_harbison at yahoo.com>
> > # Date 1490327243 14400
> > #      Thu Mar 23 23:47:23 2017 -0400
> > # Node ID c053dc8a24afad24872397e5cd3f57411fc7d172
> > # Parent  d0c2db2d9f13dca534c598de050eb1919ef79059
> > repair: use context manager for lock management
>
> Sure. Queued this, thanks.
>
> > I found several other instances of acquiring the lock inside of the
> 'try', but
> > those finally blocks handle None references.  I also started switching
> some
> > trivial try/finally blocks to context managers, but didn't get them all
> because
> > indenting over 3x for lock, wlock and transaction would have spilled
> over 80
> > characters.  That got me wondering if there should be a repo.rwlock(),
> to handle
> > locking and unlocking in the proper order.
>
> We have lockmod.release() helper. We also have util.ctxmanager(), but IMHO
> it
> doesn't improve code readability that much.
>
> > It also looks like py27 supports supports multiple context managers for
> a single
> > 'with' statement.  Should I hold off on the rest until py26 is dropped?
>

I think there is room for a helper context manager (like repo.rwlock())
that obtains multiple locks and/or a transaction. This would cut down on a
lot of excessive indentation while simultaneously ensuring we're doing the
correct thing with regards to locking and transaction semantics.
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