[M3devel] cooperative suspend?

[Jay K]

cooperative suspend


Tony, you mind if I take a stab at "cooperative suspend"
fairly soon?
I can't find a good way to suspend threads on VMS.
  Or even get context in a signal handler.
It will be a boolen in Target.i3, so no existing targets affected.
  Of course I'll test it on an existing target with the boolean set wrong. :)
  
  
To optimize size instead of speed, I think the "every so often
extra generated code" should be a call to a parameter-less function.
Instead of checking a per-thread or global variable.

Something like:


VAR threadRequestingSuspend: ADDRESS;


PROCEDURE Thread.PollSuspend()
  BEGIN
    IF threadRequestingSuspend = NIL THEN RETURN END;
    PollSuspendSlow();
  END PollSuspend;


(* This is split to avoid needing a frame in PollSuspend. *)  
PROCEDURE PollSuspendSlow()
  VAR self: ADDRESS;
  BEGIN
    IF threadRequestingSuspend = NIL THEN RETURN END;
    self := GetActivation();
    IF self = threadRequestingSuspend THEN RETURN END; (* important consideration! *)
    GetContext(self.context); (* roughly *)
    self.suspended := TRUE; (* roughly *)
    WaitForResume(); (* details to be determined, either the semaphore
                      * or maybe acquire per-thread lock. *)
  END PollSuspendSlow;


The poll call could also be a function pointer and usually point to a function that does nothing.
But that'd require loading the address from a global, and calling it.
Probably more bloat than calling direct instead of indirect.


 - Jay