[libvirt PATCH v4 3/9] virthread: Introduce VIR_WITH_MUTEX_LOCK_GUARD

[Daniel P. Berrangé]

On Fri, Jan 28, 2022 at 10:59:16AM +0100, Tim Wiederhake wrote:
> Modeled after "WITH_QEMU_LOCK_GUARD" (see qemu's include/qemu/lockable.h).
> Uses "__LINE__" instead of "__COUNTER__", as the latter is a GNU extension.

GNU extensions are fine to use, as we explicitly only support GCC
or CLang which is compatible with GCC, so I'd stick with __COUNTER__.

> 
> See comment for typical usage.
> 
> Signed-off-by: Tim Wiederhake <twiederh at redhat.com>
> ---
>  src/util/virthread.h | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/src/util/virthread.h b/src/util/virthread.h
> index 6cdaf2820e..da17780908 100644
> --- a/src/util/virthread.h
> +++ b/src/util/virthread.h
> @@ -209,3 +209,23 @@ int virThreadLocalSet(virThreadLocal *l, void*) G_GNUC_WARN_UNUSED_RESULT;
>          return 0; \
>      } \
>      struct classname ## EatSemicolon
> +
> +/**
> + * VIR_WITH_MUTEX_LOCK_GUARD:
> + *
> + * This macro defines a lock scope such that entering the scope takes the lock
> + * and leaving the scope releases the lock. Return statements are allowed
> + * within the scope and release the lock. Break and continue statements leave
> + * the scope early and release the lock.
> + *
> + *     virMutex *mutex = ...;
> + *
> + *     VIR_WITH_MUTEX_LOCK_GUARD(mutex) {
> + *         // `mutex` is locked, and released automatically on scope exit
> + *         ...
> + *     }
> + */
> +#define VIR_WITH_MUTEX_LOCK_GUARD(m) \
> +    for (g_auto(virLockGuard) CONCAT(var, __LINE__) = virLockGuardLock(m); \
> +         CONCAT(var, __LINE__).mutex; \
> +         CONCAT(var, __LINE__).mutex = (virLockGuardUnlock(& CONCAT(var, __LINE__)), NULL))
> -- 
> 2.31.1
> 

Regards,
Daniel
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