Re: [boost] [FSM] Review library version update

From: Andreas Huber (ahd6974-spamgroupstrap_at_[hidden])
Date: 2007-02-05 15:41:53

Fabien Niñoles wrote:
>> In a multithreaded app this might work on some platforms, on others
>> it doesn't:
>>
>> Quote from http://msdn2.microsoft.com/en-us/library/s1sb61xd.aspx:
>> "Assigning to a static local variable is not thread safe and is not
>> recommended as a programming practice."
>>
>> Although this isn't very concise wording (IIRC, the standard says
>> that it should work for literals assigned to PODs) it seems clear
>> that it won't work for non-PODs...
>
>
> For assignation, sure, but I don't see any in my code...

As I said the wording isn't very concise. I think it's obvious that it 
will not work if state_dispatcher has a non-trivial ctor (which I assume 
it has).

>  However, if
> that's bother, I think then only something like Loki Singleton
> pattern will do.
> You then need a double lock for accessing it correctly, something
> like this:
>
> static state_dispatcher const& get()
> {
>    static state_dispatcher* pInstance;
>    scoped_lock first_lock(m_mutex1)
>    if (!pInstance)
>    {
>       scoped_lock second_lock(m_mutex2);
>       if (!pInstance)
>       {
>          pInstance = new state_dispatcher;
>       }
>    }
>    return *pInstance;
> }

>From where did you get m_mutex1 & m_mutex2?? Where are they initialized?

-- 
Andreas Huber
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