Re: [boost] platform specific structures

From: Peter Dimov (pdimov_at_[hidden])
Date: 2004-09-20 07:17:43

Matt Hurd wrote:
> On Mon, 20 Sep 2004 14:25:46 +0300, Peter Dimov <pdimov_at_[hidden]>
> wrote:
>>
>>
>> Matt Hurd wrote:
>>>> Peter Dimov <pdimov_at_[hidden]> wrote:
>>>>> Matt Hurd wrote:
>>>>> I'm interested in getting something like "needs_lock" below into
>>>>> the normal traits, perhaps as part of boost thread.  It informs
>>>>> you whether of not an operation on such a contiguous block needs
>>>>> a lock to be atomic.
>>>>>
>>>>> For example, on ia32 32 bit aligned ops are atomic, on ia64 it is
>>>>> 64 bit.  doubles on ia32 need locking to be atomic, on ia64 they
>>>>> don't.
>>>>
>>>> What do you mean by "atomic"? Do you expect the change to the value
>>>> to be visible to other threads?
>>>
>>> Just memory consistent / atomic.  That is, if you write to memory or
>>> read from memory all the bits will be guaranteed to make it as an
>>> indivisible unit.  It doesn't say anything about the timing of the
>>> visibility or ordering w.r.t. like memory transactions.
>>
>> How would you use such a thing? :-)
>
> My main current use is in a macro I use than generates getter and
> setters with and without locking for simplifying the construction
> concurrent aware classes.

But why is a concurrent-aware setter useful if its effects aren't visible to 
the other threads?