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From: Alex =?utf-8?Q?Benn=C3=A9e?= <alex.bennee@linaro.org>
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Date: Fri, 08 Apr 2016 14:02:11 +0100
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Subject: Re: [Qemu-devel] [PATCH v2 06/13] qemu-thread: add simple
 test-and-set spinlock
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To: "Emilio G. Cota" <cota@braap.org>
Cc: QEMU Developers <qemu-devel@nongnu.org>, MTTCG Devel <mttcg@listserver.greensocs.com>, Paolo Bonzini <pbonzini@redhat.com>, Peter Crosthwaite <crosthwaite.peter@gmail.com>, Richard Henderson <rth@twiddle.net>, Peter Maydell <peter.maydell@linaro.org>, Sergey Fedorov <serge.fdrv@gmail.com>


Emilio G. Cota <cota@braap.org> writes:

> From: Guillaume Delbergue <guillaume.delbergue@greensocs.com>
>
> Signed-off-by: Guillaume Delbergue <guillaume.delbergue@greensocs.com>
> [Rewritten. - Paolo]
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  include/qemu/thread.h | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
>
> diff --git a/include/qemu/thread.h b/include/qemu/thread.h
> index bdae6df..1aa843b 100644
> --- a/include/qemu/thread.h
> +++ b/include/qemu/thread.h
> @@ -1,6 +1,8 @@
>  #ifndef __QEMU_THREAD_H
>  #define __QEMU_THREAD_H 1
>
> +#include <errno.h>
> +#include "qemu/atomic.h"
>
>  typedef struct QemuMutex QemuMutex;
>  typedef struct QemuCond QemuCond;
> @@ -60,4 +62,33 @@ struct Notifier;
>  void qemu_thread_atexit_add(struct Notifier *notifier);
>  void qemu_thread_atexit_remove(struct Notifier *notifier);
>
> +typedef struct QemuSpin {
> +    int value;

If we are throwing true and false around as the only two values can we
use bool here and be consistent when setting/clearing.

> +} QemuSpin;
> +
> +static inline void qemu_spin_init(QemuSpin *spin)
> +{
> +    spin->value = 0;
> +}
> +
> +static inline void qemu_spin_lock(QemuSpin *spin)
> +{
> +    do {
> +        while (atomic_read(&spin->value));
> +    } while (atomic_xchg(&spin->value, true));
> +}
> +
> +static inline int qemu_spin_trylock(QemuSpin *spin)
> +{
> +    if (atomic_read(&spin->value) || atomic_xchg(&spin->value, true)) {
> +        return -EBUSY;
> +    }
> +    return 0;
> +}
> +
> +static inline void qemu_spin_unlock(QemuSpin *spin)
> +{
> +    atomic_mb_set(&spin->value, 0);
> +}
> +
>  #endif


--
Alex Bennée