[fpc-pascal] Traits Proposal

[Benito van der Zander]

Hi,

> If you need to create 1000 class instances each frame then you have a 
> flaw in your logic in my opinion.
>
I have more like a million class instances

For my XPath stuff, and every returned value is put in a variant-like 
class. Selecting all nodes on an GB large XML, could even create almost 
a billion class instances


I once did a benchmark. It is 10% faster to reuse the class instances 
rather than recreating them, my commit log says. And I only implemented 
one interface (actually, two interfaces, since IUnknown always gets 
pulled in, too. )


> Interfaces are not slow because they are are interfaces! When you call 
> a interface method it has the same costs as a virtual method call! And 
> the cost for reference counting that interfaces have right now would 
> be there for ARC as well.


But it is not calling the method, it is calling the wrapper function

That is a additional second method call/jump for every interface method 
call.


E.g. _AddRef on TInterfacedObject as an interface, does not call 
TInterfacedObject._AddRef, it calls this:

WRPR_$SYSTEM_$$_TINTERFACEDOBJECT_$_IUNKNOWN_$_1_$_SYSTEM$_$TINTERFACEDOBJECT_$__$$__ADDREF$$LONGINT 

0000000000424600 4883ef10                 sub    $0x10,%rdi
0000000000424604 e997f8feff               jmpq   0x413ea0 
<SYSTEM$_$TINTERFACEDOBJECT_$__$$__ADDREF$$LONGINT>


Bye,
Benito
On 16.02.21 19:48, Sven Barth via fpc-pascal wrote:
> Ryan Joseph via fpc-pascal <fpc-pascal at lists.freepascal.org 
> <mailto:fpc-pascal at lists.freepascal.org>> schrieb am Di., 16. Feb. 
> 2021, 19:21:
>
>     >
>     > There we have:
>     >
>     > * slower creation of the class, because each implemented
>     interface adds another VMT reference to the class which needs to
>     be initialized.
>
>     How bad is this? We need to make a test case we can profile. For
>     example if you have a game that creates 1000 classes 60 frames per
>     second. If adding interfaces to the classes hurts this process we
>     may have a deal breaker.
>
>
> If you need to create 1000 class instances each frame then you have a 
> flaw in your logic in my opinion.
>
>
>     > * slow reference counting. Especially if it is thread safe and
>     exception safe with the implicit exception block
>
>     It's a whole other topic but FPC needs opt-in ARC at the language
>     level for classes. Interfaces are not only slow but then you need
>     to pass around a reference to the interface instead of the class
>     you actually care about. It makes no sense to me whatsoever.
>
>
> Interfaces are not slow because they are are interfaces! When you call 
> a interface method it has the same costs as a virtual method call! And 
> the cost for reference counting that interfaces have right now would 
> be there for ARC as well.
>
> Regards,
> Sven
>
>
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