[PATCH 03/43] conf: nwfilter_ipaddrmap: convert virMutex to GMutex

Pavel Mores pmores at redhat.com
Wed Apr 15 12:43:27 UTC 2020

On Sat, Apr 11, 2020 at 08:15:15PM +0200, Rafael Fonseca wrote:
> On Fri, Apr 10, 2020 at 7:06 PM Laine Stump <laine at laine.org> wrote:
> > > Beyond that, why not just use the G_*() macros for *all* locks in
> > > libvirt instead of only using them in cases of static locks? It seems
> > > strange to use the convenience macros in some cases and the raw
> > > functions in others. (I'm looking at this with 0 experience using the
> > > Glib locks, so maybe there's something basic I'm just not aware of -
> > > maybe something necessary is missing from the G_LOCK() macros?).
> >
> >
> > Okay, I already see that the G_LOCK macros don't cover everything - no
> > recursive mutexes and no RW mutexes for example. Too bad - it would be
> > good to be consistent.
> Yes, that's one issue. Another is: how do you use those macros with
> locks inside structs? You can't do `G_LOCK(obj->parent.lock)` because
> it'll result in `g_mutex_lock(&g__obj->parent.lock_lock)` which is
> wrong. You'd have to use the raw function
> `g_mutex_lock(obj->parent.LOCK_NAME(lock))` anyway, which imho, is
> even worse than `g_mutex_lock(&obj->parent.lock)`. The same issue
> happens when using mutexes with conditions: `g_cond_wait(cond,
> obj->parent.LOCK_NAME(lock))
> ` instead of just `g_cond_wait(cond, obj->parent.lock)`. So they work
> better for statically-defined locks
> I don't mind doing whichever you guys prefer, just let me know.

Looking at the source code, the name mangling is pretty much all that the
G_LOCK_DEFINE* macros do.  So - besides some logging - the only advantage to
using them is that you don't have to mangle the lock names manually and can use
names of existing variables as the macros' arguments.

Considering the above, I'd say either use the macros and don't mangle the lock
names in their arguments manually, or don't use the macros.  If consistent
style is a priority I'd lean towards raw functions - unlike the macros, they
can be used everywhere, and having to mangle the lock names by hand doesn't
seem a huge burden to me.  We do loose the logging that the macros do but in my
experience, mutex logging often doesn't turn out as useful in practice as it
might first appear...


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