development efforts on the Solaris side.

[Theo Schlossnagle]

On Feb 14, 2008, at 5:48 AM, Dag-Erling Smørgrav wrote:

> Theo Schlossnagle <theo at omniti.com> writes:
>> [re: stv = stevedores = stevedores->next;]
>>
>> [...]  Was worried that the assumption that both assignments were
>> atomic.  One is, then the next is.  Perhaps that doesn't matter.  It
>> does seem like a hard to trigger race condition to me because while
>> the assignment is atomic, the access to stevedores->next is not
>> guaranteed to be view consistent in that assignment:
>>
>> T1: get stevedores->next in R(T1,a)
>> T2: get stevedores->next in R(T2,a)
>> T1: set stevedores to R(T1,a)
>> T2: set stevedores to T(T2,a)
>>
>> Now T1 and T2 both "advanced the pointer" but they did the same work
>> and the stv they have is the same.  Is that not a problem?  Perhaps
>> I don't understand the impact of that scenario correctly.
>
> There is a race, but it's irrelevant.  The point of this code is to
> spread the load between the stevedores.  It doesn't matter if two
> simultaneours allocations go to the same stevedore as long as *all*
> allocations don't go to the same stevedore.  It will balance out in
> the long run.

The comment made me think that the code was relying on different  
threads getting different stevedores for safety reasons -- not  
efficiency.  Thanks for clearing that up.

--
Theo Schlossnagle
Esoteric Curio -- http://lethargy.org/
OmniTI Computer Consulting, Inc. -- http://omniti.com/