druntime thread_needLock()
Fawzi Mohamed
fmohamed at mac.com
Sun Dec 7 02:01:44 PST 2008
On 2008-12-07 09:23:01 +0100, Sean Kelly <sean at invisibleduck.org> said:
> Fawzi Mohamed wrote:
>> On 2008-12-07 03:48:40 +0100, Sean Kelly <sean at invisibleduck.org> said:
>>>
>>> Not true. You would need an acquire barrier in thread_needLock.
>>> However, on x86 the point is probably moot since loads have acquire
>>> semantics anyway.
>>
>> You would need a very good processor to reorder speculative loads
>> before a function call and a branch. As far as I know even alpha did
>> not do it.
>
> But if thread_needLock() is inlined...
>
>> A volatile statement will probably be enough in all cases, but you are
>> right that to be really correct a load barrier should be done, an even
>> in a processor where this might matter the cost of it in the fast path
>> will be basically 0 (so still better than a lock).
>
> Aye. I'd do this if there were a common use case that justified it,
> but I don't see one.
I fully agree with you (see my answer to Robert Fraser)
>
>
> Sean
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