Re: [Qemu-devel] [PATCH 2/5] lockable: add QemuLockable

[Eric Blake <eblake@redhat.com>]

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On 01/25/2018 11:59 AM, Paolo Bonzini wrote:
> QemuLockable is a polymorphic lock type that takes an object and
> knows which function to use for locking and unlocking.  The
> implementation could use C11 _Generic, but since the support is
> not very widespread I am instead using __builtin_choose_expr and
> __builtin_types_compatible_p, which are already used by
> include/qemu/atomic.h.
> 
> QemuLockable can be used to implement lock guards, or to pass around
> a lock in such a way that a function can release it and re-acquire it.
> The next patch will do this for CoQueue.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---

> +
> +static inline __attribute__((__always_inline__)) QemuLockable *
> +qemu_make_lockable(void *x, QemuLockable *lockable)
> +{
> +    /* We cannot test this in a macro, otherwise we get * compiler

Spurious '*' ?

> +     * warnings like "the address of 'm' will always evaluate as 'true'".
> +     */
> +    return x ? lockable : NULL;
> +}
> +

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


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