Re: [boost] [lockfree::fifo] Review

Subject: Re: [boost] [lockfree::fifo] Review
From: Chris M. Thomasson (cristom_at_[hidden])
Date: 2010-01-04 02:12:21

"Chris M. Thomasson" <cristom_at_[hidden]> wrote in message 
news:hgoao1$klu$1_at_ger.gmane.org...
[...]
>> which provides a nice, contention-free (no stores by readers!) mechanism 
>> to share read-mostly state.
>
> Interesting... Humm, that kind of reminds me of a sequence lock:
>
> <membars aside for a moment>
> _______________________________________________________________
> template<typename T>
> struct sequence_lock
> {
>    T m_object; // = T()
>    uint32_t m_version; // = 0
>    mutex m_mutex;
>
>
>    T read()
>    {
>        for (;;)
>        {
>            if (LOAD(&m_version) % 2) yield(), continue;
>
>            T object = m_object;
>
>            if (LOAD(&m_version) % 2) yield(), continue;

I forgot to load and compare the version!

let me fix that:
___________________________________________________________
     T read()
     {
         for (;;)
         {
             uint32_t version1 = LOAD(&m_version);

             if (! (version1 % 2))
             {
                 T object = m_object;

                 uint32_t version2 = LOAD(&m_version);

                 if (version1 == version2)
                 {
                     return object;
                 }
             }

             backoff();
         }
     }
___________________________________________________________

Sorry about that!

;^o

>    void write(T const& object)
>    {
>        mutex::scoped_lock lock(m_mutex);
>
>        STORE(&m_version, LOAD(&m_version) + 1);
>
>        m_object = object;
>
>        STORE(&m_version, LOAD(&m_version) + 1);
>    }
> };
> _______________________________________________________________