Re: What's all this about Swarm modifying the runtime?

[W . Northcott]

Paul wrote
> I don't even really know what "runtime" means, so take this with a grain
> of salt.

Basically the runtime is a set of C functions which implement the nitty 
gritty of objects messages etc.

The runtime in GNU is libobjc.  Swarm builds its own from the source files 
in the libobjc directory.  The standard GNU runtime is part of the gcc 
package and will typicaly be installed in /usr/lib with symlinks from 
elsewhere.   I think the Apple runtime is libobjc4.dylib.  The Darwin 
project is certainly libobjc4.

> Does Swarm really use a different runtime?

Yes really.  To convince yourself, alter the linking specifications in the 
build scripts to link to the standard GNU library.  You will get a heap of 
missing symbols.

This is a major portability issue.  If Swarm used the GNU runtime , it 
would be trivial to recompile the code on MacOS X using the Apple runtime 
which is essentially identical at the Objective-C API level although 
totally different at the C function or binary level.

> Swarm can be built with the stock gcc.  There is an optional patch we
> make to gcc to allow method functions, but it is not necessary.  I
> suspect that since gcc 3.2 has many optimizations incorporated from the
> Apple research team (they claim messaging is now orders of magnitudes
> faster) perhaps we don't even benefit from that one little gcc patch.

The method functions as you say can be patched around.  However the show 
stopper is the system of phases for objects.  (createbegin createend etc)  
Currently this is implemented via the modified runtime, which from an OO 
perspective is unspeakably nasty.  In principle, it should be possible to 
achieve a similar effect on the standard runtime, but it would require 
large amounts of the Swarm code to be rewritten.  Scott Christley, who 
understands this much better than I, has written quite a bit about this.

> If you get a gcc snapshot on or after 2002-09-09 (not 3.2, but rather

I am desperately trying to make Swarm easier to install.  At the moment 
there is a long list of libraries and tools that need to be installed on 
any system to get Swarm to compile.
So I stick to using Apple compilers.  AFAIK the last update to the Apple 
sources from the FSF tree was done on 25 August.  However, there is 
probably neglible functional difference between what you refer to as  3.2 
snapshot and the current Apple surces.

<RANT>MacOS X should be the best and easiest platform on which to install 
and use Swarm.  It is derived directly from the NextStep platform which I 
believe was used for the original Swarm development.  Also like Swarm it 
is Objective-C based.  It comes out of the box with an excellent ObjC IDE 
replete with compiler, debuggers, profilers, cvs and a host of other 
tools.  All the required libraries compile and run with little if any 
modification.  Although MacOS X is proprietry, all of it which is of 
interest to Swarm programmers is opensource.   Apple are investing very 
heavily in this opensource code including the compilers and runtime. More 
than that, they are very responsive to the needs of the opensource 
community.  Within days of Marcus sending them a clear explanation of the 
nested functions issue, they fixed the compiler code.  However, neither 
Apple nor the FSF are ging to change their runtime libraries or compilers 
to incorporate Swarm weirdness. </RANT>

> updates that come after it), you can build Swarm if you apply 3 small
> patches to Swarm itself.  (I can give you those patches.)

The best place for the patches would be on the Savannah site.  If you want 
to send them to me, I will put them up.

> Doesn't that mean we are using the GNU runtime?

As above, NO.

Bill Northcott

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