[Qemu-devel] [PATCH 3/3] glib: add compat wrapper for GStaticMutex

[Michael Tokarev]

Stefan Hajnoczi:

> Avoid duplicating ifdefs for the deprecated GStaticMutex API by
> introducing compat_g_static_mutex_*() in glib-compat.h.
>
> GStaticMutex users should use the compat API to avoid dealing with
> deprecation.

To my taste this is a wrong(ish) approach.

GStaticMutex is nothing more than a pointer to GMutex wrapped in an internal
structure, and each function from g_static_mutex_* family first checks for
this pointer, whenever it is initialized, and calls g_mutex_new() if not.
So if there's a good place to actually init (allocate) a GMutex, it is better
to use it directly instead of checking for the init in every place.

(Note also that this checking itself may need a protection using a mutex,
to avoid 2 threads allocating the same GStaticMutex ;) -- this is done in
g_static_mutex_get_mutex_impl() inside glib).

But that's cosmetics.

More to the point is that this is re-introduction of old API for new program.
It'd be very nice if we were able to actually use the new API everywhere,
instead of re-introducing old API.

And this introduces some (light) wrapper #ifdefery too.

So we not only will use the old API in the code, we also will use wrappers
for almost everything.  So it becomes rather clumsy.

It is, I think, better to try to switch to the new API as much as possible,
or to use our own types and wrappers instead, without resoting to use
foo_compat_deprecated_* (where "deprecated" part comes from staticmutex --
ie, instead of regular g_mutex_foo, we use g_compat_static_mutex_foo).

Other the bit of clumsiness, this should work.


> +/* GStaticMutex was deprecated in 2.32.0.  Use the compat_g_static_mutex_*()
> + * wrappers to hide the GStaticMutex/GMutex distinction.
> + */
> +#if GLIB_CHECK_VERSION(2, 32, 0)

It is actually deprecated in 2.31, even if the glib docs says 2.32.
Probably not a big deal, as, I think, there's no 2.31 glib in the wild
due to bugs in there, so they had to quickly release 2.32.

Thanks,

/mjt