Re: [boost] Review request: Boost.FSM

From: Andrey Semashev (andysem_at_[hidden])
Date: 2007-01-08 16:48:54

Hello Steven,

Monday, January 8, 2007, 11:26:29 PM, you wrote:

> AMDG

> Andrey Semashev wrote:
>> Oh, you're right. But isn't it enough just to mark "m_fInitialized" as
>> "volatile"? According to 1.9/7 it would enforce the compiler to
>> initialize "m_StatesInfo" prior to setting "m_fInitialized".
>>   
> No, m_StatesInfo has to be volatile too.

Why? The Standard says all side effects prior to access to a volatile
object will be completed at a sequence point (1.9/7, 1.9/11). There is
a sequence point after returning from a function (1.9/17). At this
sequence point all expressions of the function will be complete (IOW,
m_StatesInfo will be initialized). So, in our case no matter what a
compiler does, the call to "init_states_info" must be done before
"m_fInitialized" assignment, shouldn't it?

Actually, thinking of is some more I got some doubts about wether a
compiler is allowed to shuffle expressions. The "init_states_info"
function call and "m_fInitialized" assignment are both
full-expressions and thus have sequence points at completion of
each of them (1.9/16). So they should be executed in the the same
order as they written in code. Sorry if I'm asking dumb questions, I'm
just trying to get to the bottom of this. Am I wrong?

-- 
Best regards,
 Andrey                            mailto:andysem_at_[hidden]