Callbacks from C into Squeak

Andreas Raab andreas.raab at
Thu Dec 14 17:57:25 UTC 2006

   - Andreas

John M McIntosh wrote:
> Well you can't callback from C to Squeak, once you are in a primitive 
> call the interpeter is suspended, triggering a GC event requires
> special care to ensure object pointers you many have will still be valid 
> (remapped) after the GC completes.  You can of course do a limited set 
> of VM calls to manipulate or make new object, but that does not include 
> running byte codes.  Likely this can be overcome by $ (euros preferred).
> Other options include running a VM (or VMs) as a sub process and talking 
> to it via pipes or shared memory areas for it to do computational work.  
> Technially this is done by mac carbon and unix VM when they run headless 
> to provide support as a browser plugin.
> On Dec 14, 2006, at 6:17 AM, daniel poon wrote:
>> Callbacks from C into Smalltalk
>> We currently use VSE (Visual Smalltalk Enterprise). If you have a C
>> callback into VSE, while the callback is running, it is very difficult
>> to debug. If the callback halts, or there is an error, you can't debug
>> and resume in the normal way that you can in Smalltalk. Apparently this
>> is something to do with VSE using the machine stack as the Smalltalk
>> stack.
>> However, one of the nice things about VSE is: if I put a halt in the
>> callback, will I see the entire stack, including the methods before the
>> initial entry into C. Also if I throw an exception in the call back
>> that is not caught in the callback, will it be caught further down the
>> stack by code running before the initial entry into C. If it a
>> resumable exception, I can resume as per normal.
>> Now, we do a lot of numerical computing, re-using all the C and Fortran
>> libraries that are already out there. It is common in a numerical
>> library to use callbacks. Say you want to integrate f(x). The
>> integrator is written in Fortran, and f(x) is written in Smalltalk. You
>> need a way for the integrator to call f(x), and you do that with a
>> callback. So to leverage these libraries we need an easy way to do
>> callbacks, and once you have a callback you need a way of debugging
>> these callbacks that a mathematician (rather than a comuputer
>> scientist) will feel comfortable with.
>> So my questioin is: when you callback into Squeak from C/Fortran,
>> can you throw and catch exceptions, halt, debug and resume execution
>> of the callback in the normal Smalltalk way. Or does the fact that
>> you are in a callback compromise Smalltalk's usual execution?
>> Cheers
>> Daniel
> -- 
> ===========================================================================
> John M. McIntosh <johnmci at>
> Corporate Smalltalk Consulting Ltd.
> ===========================================================================

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