Re: [PATCH for-8.0 1/7] qemu/main-loop: Introduce QEMU_IOTHREAD_LOCK_GUARD

["Alex Bennée" <alex.bennee@linaro.org>]

Richard Henderson <richard.henderson@linaro.org> writes:

> Create a wrapper for locking/unlocking the iothread lock.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
> Cc: Paolo Bonzini <pbonzini@redhat.com> (maintainer:Main loop)
> ---
>  include/qemu/main-loop.h | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
>
> diff --git a/include/qemu/main-loop.h b/include/qemu/main-loop.h
> index 3c9a9a982d..c25f390696 100644
> --- a/include/qemu/main-loop.h
> +++ b/include/qemu/main-loop.h
> @@ -343,6 +343,35 @@ void qemu_mutex_lock_iothread_impl(const char *file, int line);
>   */
>  void qemu_mutex_unlock_iothread(void);
>  
> +/**
> + * QEMU_IOTHREAD_LOCK_GUARD
> + *
> + * Wrap a block of code in a conditional qemu_mutex_{lock,unlock}_iothread.
> + */
> +typedef struct IOThreadLockAuto IOThreadLockAuto;
> +
> +static inline IOThreadLockAuto *qemu_iothread_auto_lock(const char *file,
> +                                                        int line)
> +{
> +    if (qemu_mutex_iothread_locked()) {
> +        return NULL;
> +    }
> +    qemu_mutex_lock_iothread_impl(file, line);
> +    /* Anything non-NULL causes the cleanup function to be called */
> +    return (IOThreadLockAuto *)(uintptr_t)1;

Oh hang on, what black magic is this. Does the compiler do a NULL check
before calling the cleanup?

> +}
> +
> +static inline void qemu_iothread_auto_unlock(IOThreadLockAuto *l)
> +{
> +    qemu_mutex_unlock_iothread();
> +}
> +
> +G_DEFINE_AUTOPTR_CLEANUP_FUNC(IOThreadLockAuto, qemu_iothread_auto_unlock)
> +
> +#define QEMU_IOTHREAD_LOCK_GUARD() \
> +    g_autoptr(IOThreadLockAuto) _iothread_lock_auto __attribute__((unused)) \
> +        = qemu_iothread_auto_lock(__FILE__, __LINE__)
> +
>  /*
>   * qemu_cond_wait_iothread: Wait on condition for the main loop mutex
>   *


-- 
Alex Bennée