Threads and asyncs

[Marius Vollmer]

Hi,

currently, when you mark a system-async, it is run at the next 'safe'
point.  This does not take the current thread into account and thus,
you can not have thread-specific system-asyncs.  One example where you
might want to have a thread-specific async is when you want to
interrupt the computation in a certain thread, the way you can now
interrupt the repl via C-c.

I would like to specify explicitely that marking a system-async will
run its thunk in the thread that did the marking.  That should not be
a large change since the next safe point will most likely occur before
the next thread switch.

Also, I'd like to add a function that marks a system-async for a
specified thread.  The async would run at the next safe point in that
thread.

The implementation can be changed from a global list of system-asyncs,
each with a mark, to a per-thread list of marked system-asyncs.
Marking a system-asnyc for a thread would add that system-async to the
thread's lists.  SCM_ASYNC_TICK would check whether the current
thread's list is non-empty.  Also, a thread would wake up when it is
blocked and run its asyncs anyway.

'sigaction' can be extended to allow marking of an async for a
specified thread.

With this change, an async would simply be a thunk.  We could just use
the thunk directly and deprecate the async abstraction.

OK?

(Non-system asyncs would not be affected.)

-- 
GPG: D5D4E405 - 2F9B BCCC 8527 692A 04E3  331E FAF8 226A D5D4 E405