[fedora-java] gcj-dbtool --rebuild

[Bryce McKinlay]

Andrew Haley wrote:

>Gary Benson writes:
> > Thomas Fitzsimmons wrote:
> > > Here's what "gcj-dbtool --rebuild" needs to do:
> > > 
> > > Merge all db files in "$prefix/lib/gcj-$gcc_version/classmap.db.d/" into
> > > "$prefix/lib/gcj-$gcc_version/classmap.db".
> > >
> > > Even better for FC5 would be eliminating the need for individual .db
> > > files altogether.
> > 
> > This would require the hashes to be stored in the .so, which I don't
> > think they are at present.  Is this something which is possible?
>
>Yes.  It is part of the Grand Plan.  But reading the hashes out of a
>.so is going to be far slower than out of a .db.  It wouldn't be
>practical if you had thousands of them.
>  
>
With hashes stored in the .so's, we'd still want to keep the .db as a 
sort of cache. The advantage would be that updating/rebuilding the db 
becomes much faster, as dbtool just needs to compare the hashes in each 
.so with what is in the database rather than reading all the bytecode 
and recomputing the hashes.

It would be too slow for the general case to have libgcj reading hashes 
from all the shared libraries at runtime, but it would allow things to 
work better in the case where the classes in a particular .so at runtime 
don't match the contents of the db - something that could happen during 
development or in case someone forgets to run dbtool. Currently we just 
quietly fall back to the interpreter in that case, resulting in 
(seemingly) mysterious performance problems.

Bryce