Lately I've been trying out new (to me) languages and one of the things I keep running into is "fake" threading support, i.e. the threads are "real" in the sense they can preempt one another and map to native OS threads, but in practice they can't actually run at the same time so there is no parallel speedup (concurrency, not parallelism). Python has the GIL, and Racket has futures that technically can run simultaneously but only as long as no thread allocates -- which is a pretty big limitation since so much as sneezing in Lisp causes an allocation. Python also has the multiprocessing library which works in for some problems but not others and Racket has the places mechanism which is almost identical and has the same limitations.
What is the state of multithreading in Perl 6 (MoarVM)? Specifically: * Can two threads preempt one another? * Is there a GIL? (Think I asked around before and the answer is no) * Can two threads allocate at the same time? * Does a GC stop all threads? * Are there any other common operations, besides allocation, that trigger locks? * If allocation triggers a lock, how feasible is it to write in an allocation free style? Hyper operators and junctions and future promises of autothreading are great, but without answers to these it's hard to know whether the threading is or will be actually worth taking advantage of. I've noticed nobody outside the CLR and the JVM seems to actually implement real multithreaded GC so I'm a bit skeptical. It seems like a common implementation stumbling block and a genuinely hard problem. Joe G.
