Getting locks and sharing: was RE: Getting concurrency

[Matthias Lang]

Reto Kramer writes:

 > Where can I learn about what's been done in the past and get a sense of 
 > the Erlang specific challenges and the complexity of such a multi CPU 
 > aware VM?  Did the HiPE group attempt this in the past?

Pekka Hedqvist and Tony Rogvall (not the HIPE group) implemented
exactly such a beast for the (now defunct) JAM VM. I can't find the
report online, but here's a summary from memory:

   - We implemented a multithreaded erlang VM by hacking the JAM
     VM.

   - On a four-CPU machine, it got an almost linear speedup on
     code which wasn't entirely contrived

   - Our VM modifications got to the "99% complete" stage, but then the BEAM 
     VM came out and we felt ill at the thought of having to do
     it all again. Suddenly, other problems looked much more interesting.

Matthias