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From: "Daniel P. Berrangé" <berrange@redhat.com>
To: "Alex Bennée" <alex.bennee@linaro.org>
Cc: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH 3/4] docs: document use of automatic cleanup functions in glib
Date: Wed, 28 Aug 2019 16:20:28 +0100
Message-ID: <20190828152028.GM2991@redhat.com> (raw)
In-Reply-To: <878srd5nlz.fsf@linaro.org>

On Wed, Aug 28, 2019 at 04:14:00PM +0100, Alex Bennée wrote:
> > +The cleanup functions are not restricted to simply free'ing memory. The
> > +GMutexLocker class is a variant of GMutex that has automatic locking and
> > +unlocking at start and end of the enclosing scope
> > +
> > +In the following example, the `lock` in `MyObj` will be held for the
> > +precise duration of the `somefunc` function
> > +
> > +    typedef struct {
> > +        GMutex lock;
> > +    } MyObj;
> > +
> > +    char *somefunc(MyObj *obj) {
> > +        g_autofree GMutexLocker *locker = g_mutex_locker_new(&obj->lock)
> > +        g_autofree char *foo = g_strdup_printf("foo%", "wibble");
> > +        g_autoptr (GList) bar = .....
> > +
> > +        if (eek) {
> > +           return NULL;
> > +        }
> > +
> > +        return g_steal_pointer(&foo);
> > +    }
> 
> I would personally prefer we get some RFC patches for auto-unlocking under our
> belt before we codify it's usage in our developer docs. Locking is a
> fickle beast at the best of times and I'd like to see where it benefits
> us before there is a rush to covert to the new style.
> 
> For one thing the only uses I see of g_mutex_lock is in our tests, the
> main code base uses qemu_mutex_lock. How would we go about registering
> the clean-up functions for those in the code base?

Ideally we could just relpace qemu_mutex with g_mutex, but if that's
not possible we would have to create a clone of GMutexLocker as
QemuMutexLocker doing exactly the same thing. It is a shame to reinvent
the wheel with our threading code though.

/me tries to remember what it was that we can do with QEMU's threads
that we can't do with GLib's threads.

Regards,
Daniel
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  reply index

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-23 16:39 [Qemu-devel] [PATCH 0/4] docs: add docs about use of automatic cleanup functions Daniel P. Berrangé
2019-08-23 16:39 ` [Qemu-devel] [PATCH 1/4] docs: convert CODING_STYLE and HACKING to markdown syntax Daniel P. Berrangé
2019-08-28 12:25   ` Alex Bennée
2019-08-28 13:08     ` Daniel P. Berrangé
2019-08-23 16:39 ` [Qemu-devel] [PATCH 2/4] docs: merge HACKING.md contents into CODING_STYLE.md Daniel P. Berrangé
2019-08-23 19:35   ` Eric Blake
2019-08-28 15:06     ` Alex Bennée
2019-08-28 15:10       ` Daniel P. Berrangé
2019-08-23 16:39 ` [Qemu-devel] [PATCH 3/4] docs: document use of automatic cleanup functions in glib Daniel P. Berrangé
2019-08-23 19:53   ` Eric Blake
2019-08-28  9:00   ` Stefan Hajnoczi
2019-08-28 15:14   ` Alex Bennée
2019-08-28 15:20     ` Daniel P. Berrangé [this message]
2019-08-28 16:04       ` Alex Bennée
2019-08-23 16:39 ` [Qemu-devel] [PATCH 4/4] docs: add table of contents to CODING_STYLE.md Daniel P. Berrangé
2019-08-23 21:48 ` [Qemu-devel] [PATCH 0/4] docs: add docs about use of automatic cleanup functions Marc-André Lureau
2019-08-28 12:30   ` Alex Bennée
2019-08-28 13:07     ` Daniel P. Berrangé

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