[Vm-dev] Explicitly avoiding process switch

Nicolas Cellier nicolas.cellier.aka.nice at gmail.com
Thu Aug 11 11:17:36 UTC 2011


I would properly comment the places where this "ATOMIC" operation is
really used.

Nicolas

2011/8/11 Mariano Martinez Peck <marianopeck at gmail.com>:
>
> Hi guys. We were discussing yesterday with Marcus about the following....
>
>  I remember a problem we have in Pharo because of changing "foo == nil" to "foo isNil"  in some important places like Process/Delay/Semaphore. Such change introduces a suspension point, where if I understand correctly, the scheduler can switch to another process only during method sends. #== is optimized with a special bytecode and there is no message send. Sending #isNil is a message sent, and hence we introduce a suspension point. In 99% of the cases this is not a problem.  But I can imagine that there are places (mostly those related to Process/Delay/Semaphore) where this changes can be very very bad.
>
>
> To do some experiments, I want to remove the bytecode for #== but of course, I think I will have all these problems. And there are more. Marcus told me that some optimizations done by the compiler end up sending #==. And I also remember some code he told me (I think it was #allObjectsDo:) that would never finish because of the block closure objects creation.
>
> So...what about making the necessity of NOT sending a message or NOT introducing a suspension point more explicit?  first we should have the support for that and second know each place where we need them.
>
> The most basic thing I can think of is doing something like:
>
> (ParseNode classVarNamed:  'StdSelectors') at: #== put: #bytecodedEqualEqual.
> Compiler recompileAll.
>
> And put a nice comment why one may want to use #optimizedEqualEqual. But again, in which places should I change #== for #bytecodedEqualEqual
>
>
> Any thought or idea about them is really appreciated.
>
> Thanks
>
>
> --
> Mariano
> http://marianopeck.wordpress.com
>
>
>


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