Re: objective-c: how slow ?

[Nicola Pero]

> does the current objc compiler/runtime optimizes in some way
> message lookups (inline caches, polymorphic inline caches,...).

> PS:
> Polymorphic inline caches  (PIC) have the cost of a test and a direct 
> jump in the best case (cache hit) and 3 or 4 tests (pipelined) and a 
> normal method lookup. There could be performance issues because of the 
> self-modifying code (icache flushes) but a cache update should not 
> happen frequently.
> Please refer to the Self prototyping OO language implementation,
> and documentation for furhter informations look at: 
> http://www.sun.com/research/self/

Thanks for the pointers, I didn't know about that and it was a very
interesting reading. 

Plainly, my answer is to your suggestion of using inline caches in the
Objective-C runtime is that the current Objective-C runtime can message at
a very high speed in multithreading, in a totally thread-safe way.  The
current method cache is amazingly designed in such a way to run
thread-safe without locks, thus it is thread safe without incurring *any*
thread lock overhead.

My feeling reading about inline caches is that they require self-modifying
code, and for the solution to be viable you would need to have
self-modifying code which can run multithreading in a thread-safe way
without using locks (as adding thread locking would kill the performance). 
It might actually be possible to implement it, but if it is, it is not
going to be trivial.