[Sbcl-devel] (p)threads and amd64

[Daniel B. <da...@te...>]

Subscribers to the sbcl-commits list will have observed already that
I've been hacking amd64 threads.  IRC denizens will know that it's
based on pthreads this time, not on clone().  The current status is

- the basic runtime support stuff (thread creation, gc, etc) is there.
   Except for the cleanup routines, which aren't.
- the lisp support stuff (mostly involves vops for special variable
   operations) is there
- it builds, compiles PCL and dumps a core capable of executing 
   (sb-thread:make-thread (lambda () (sleep 1) (format t "hello~%")))

Untested or known to be missing
- stack exhaustion checking is broken - because, well, it's always the
   first thing to break
- almost anything to do with locking, though the futex locking is still in
   there and still ought still to work, given that I'm still on a
   Linux system.  Obviously it would be nice to remove this
   requirement, though, so that other platforms with pthreads can also
   build threaded sbcl
- any kind of stress testing
- the assembly stuff is believed not to be saving/restoring all the 
   registers it needs to - at least, this is not working on jsnell's
   system

FAQ

Q1) why pthreads now when you previosuly said it was crap?
A1) No, I said that _LinuxThreads_ was crap - and indeed it was.  Happily,
    it's obsolete these days.

Q2) segment registers?
A2) No, the amd64 has more than a stupidly small number of general
    purpose registers available, so we've dedicated r12 to thread base

Q3) thread objects?
A3) may well be forthcoming.  pthreads aren't identified by pids as 
    clone-based threads are, but by pointers (actually, on
    sufficiently weird systems even this isn't true - a pthread_t
    may even be a structure) which look really ugly when printed.

Q4) other architectures?
A4) should be possible.  you need to choose a thread base register, 
    amend call_into_lisp to load pthread_getspecific(specials) into
    it, and create new threaded vops for lots of special variable
    stuff (compiler/target/cell.lisp), and macros for thread-safe
    pseudo-atomic/allocation stuff (compiler/target/macros.lisp).
    And probably some runtime stuff too, but reading the diff should
    give you some clues

Q5) other OSes?
A5) see above: we're still using futexes 

Q6) where?
A6) on the amd64-pthread-branch cvs tag


Enjoy

-dan