Hi,
    looking at the method lookup algorithm I found that when a message 
is not understood by an object, the search for the #doesNotUnderstand: 
does not uses the global cache.
    Currently, in the method Interpreter>>lookupMethodInClass: class, 
after doing the search in the method dictionaries of the hole class 
hierarchy does:

    .... [ code that searchs on the method dictionaries.... ]
    "Cound not find a normal message -- raise exception #doesNotUnderstand:"
    self pushRemappableOop: class.  "may cause GC!"
    self createActualMessageTo: class.
    rclass _ self popRemappableOop.
    messageSelector _ self splObj: SelectorDoesNotUnderstand.
    ^ self lookupMethodInClass: rclass

    The last line shows that it looks for the #doesNotUnderstand: using 
the "lookupMethodInClass:". It means that the search will start directly 
on the method dictionaries, not the global lookup cache. Just changing 
that line for:

    (self lookupInMethodCacheSel: messageSelector class: rclass) 
ifFalse: [ self lookupMethodInClass: rclass ]. "(No return needed, it is 
not used...)"

    will double the search speed.
    I've try the change on the InterpreterSimulator (I have an old 
version were it still works) and everything works as usual but the 
search for #doesNotUnderstand: is much faster.
    I could not try the change on a compiled VM because I don't have a C 
compiler with me right now, but for sure it is an easy change that the 
VM's guys can try.

    On the current version, after it looks for the #doesNotUnderstand: 
method, it store the result on the global lookup cache, but it never 
uses it!! (unless an explicit #doesNotUnderstand: is sent). With the 
change I suggest, it uses the cache not matter if the send is implicit 
or explicit.

    Well, I hope it helps.

    Bye,
    Hernan.

-- 
______________________________
Lic. Hernán A. Wilkinson
Gerente de Desarrollo y Tecnología
Mercap S.R.L.
Tacuari 202 - 7mo Piso - Tel: 54-11-4878-1118
Buenos Aires - Argentina
http://www.mercapsoftware.com
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