On 10/16/07, Jason Orendorff <jason.orendorff@gmail.com> wrote:
GIL-slayers take note. Here are two papers about concurrent reference counting:
An On-The-Fly Reference Counting Garbage Collector for Java Levanoni and Petrank, 2001. http://www.cs.technion.ac.il/~erez/Papers/refcount.ps
Efficient On-the-Fly Cycle Collection Paz, Bacon, Kolodner, Petrank, and Rajan, 2005. http://www.cs.technion.ac.il/%7Eerez/Papers/CycleCollection.ps
"On-the-fly" means the algorithm is neither "fully concurrent" nor "stop the world". Rather, each thread pauses occasionally to do some work. Instead of a GIL, you have a lock that covers this periodic bookkeeping.
The details are awfully complex, but there may be insights worth gleaning regardless.
A key assumption of these papers (and presumably most such papers) is that you have a true tracing GC to fall back on, not one bootstrapped from reference counts like CPython has. This means that long-lived or shared objects can disable reference counting entirely, and not face the severe contention it would otherwise create. -- Adam Olsen, aka Rhamphoryncus