Re: [Kissme-general] Re: Proposal for changes to Classpath's JNI libraries

[Artur Biesiadowski]

Etienne M. Gagnon wrote:

> So, you probably agree that adding an indirection for doing "blocking
> calls" and providing VM-specific implementation of those calls is not
> a good idea.


Please note that this trick is more useful then just making life easier 
for Kissme at the moment (because their JNI needs to be fixed anyway I'm 
afraid). It can be also used by any jvm which wants to implement n-to-m 
thread model (or even green threads).

I suppose, that all this trick could be done even transparent for most 
jvms. Just make default indirection structure inside classpath lib and 
only allow, not require, to change it on library init by jvm. This would 
mean zero implementation cost for jvms out there, and only one or two 
extra pointer dereferences of runtime cost. It is really _null_ cost - 
these calls go through complicated code paths, ending up with context 
switch inside kernel, often also blocking on I/O. We are talking about 
adding maybe few cycles per call taking thousands cycles in best case, 
seconds in worst case (like reading from network).

Only real cost is that we need to go through all classpath native code 
and replace read by context.read (or something like this). But I suppose 
that Kissme people will probably be quite eager to do it for us ;)

Artur