[vlc-devel] [PATCH 2/3] queue: helpers for killable queues

[Steve Lhomme]

On 2020-04-11 21:12, Rémi Denis-Courmont wrote:
> This adds two functions to simplify the common case of a thread waiting on
> a queue until it is terminated.
> ---
>   include/vlc_queue.h | 42 ++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 42 insertions(+)
> 
> diff --git a/include/vlc_queue.h b/include/vlc_queue.h
> index eed69510dc..f41d72fb55 100644
> --- a/include/vlc_queue.h
> +++ b/include/vlc_queue.h
> @@ -214,5 +214,47 @@ VLC_USED;
>    */
>   VLC_API void *vlc_queue_DequeueAll(vlc_queue_t *) VLC_USED;
>   
> +/**
> + * @defgroup queue_killable Killable queues
> + *
> + * Thread-safe queues with an end flag.
> + *
> + * @{
> + */
> +
> +/**
> + * Marks a queue ended.
> + */
> +static inline void vlc_queue_Kill(vlc_queue_t *q,
> +                                  bool *restrict tombstone)
> +{
> +    vlc_queue_Lock(q);
> +    *tombstone = true;

What's the point of returning a bool if it's always the same value. And 
why not return it directly rather than using a pointer ?

> +    vlc_queue_Signal(q);
> +    vlc_queue_Unlock(q);
> +}
> +
> +/**
> + * Dequeues one entry from a killable queue.
> + *
> + * @return an entry, or NULL if the queue is empty and has been ended.
> + */
> +static inline void *vlc_queue_DequeueKillable(vlc_queue_t *q,
> +                                              ptrdiff_t offset,
> +                                              bool *restrict tombstone)
> +{
> +    void *entry;
> +
> +    vlc_queue_Lock(q);
> +    while (vlc_queue_IsEmpty(q) && !*tombstone)

I would put the bool test in a surrounding if().

> +        vlc_queue_Wait(q);
> +
> +    entry = vlc_queue_DequeueUnlocked(q, offset);
> +    vlc_queue_Unlock(q);
> +    return entry;
> +}
> +
> +/** @} */
> +
>   /** @} */
>   #endif
> -- 
> 2.26.0
> 
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