[q-lang-users] q in Q

[John C. <co...@cc...>]

Albert Graef scripsit:

> Yes, that should be possible, but I'm probably not the one who is going 
> to do it. ;-) I'd rather like to bootstrap Q in Q once we have native 
> compilation.

Well, there's a few approaches to that.  I presume a classical compiler
to assembly language chain is out.  Then there's compilation to C,
or compilation to something else (Chicken, e.g.) that compiles to C.
Then there is compilation to some standard byte code set with JIT
compilation in place, like the JVM or the CLR.  Any or all of these
would probably make q-in-Q feasible.

> I'm not sure about that. At least it would still need to do reference 
> counting, since I want objects encapsulating state to be cleaned up 
> (closing files, etc.) as soon as possible. This makes handling temporary 
> stateful objects much more convenient.

Reference counting has its own costs, though, specifically the cost of
recursive freeing, which is unpredictable in scope.

Chicken has two garbage collectors, both stop-and-copy.  The first one
is intertwined with how Chicken uses the stack.  All Scheme objects
are initially allocated on the C stack, and each Scheme procedure is
compiled into a C procedure which explicitly calls its continuation.
However, the continuation never returns.  Instead, when the stack gets
full, all live Scheme objects are copied to the heap and a longjmp()
is done to reset the stack.  A regular Baker two-space collector is
periodically run on the two halves of the heap.  Any object can have a
finalizer, which is run when the object becomes garbage.

> > Chicken doesn't do native threads, though, only call/cc based ones.
> 
> I guess that this would be a showstopper for me, with all the realtime 
> multimedia applications I'm doing.

Q has a global interpreter lock, right?  So all threads except one have
to be running C code, but which one it is can change.  I'm not sure
whether Chicken can safely spawn OS threads, but if so, they can't be
running Chicken code, at least not easily, given the mechanism
explained above.

The whole idea probably isn't practical.

-- 
John Cowan                                <co...@cc...>
Yakka foob mog.  Grug pubbawup zink wattoom gazork.  Chumble spuzz.
    -- Calvin, giving Newton's First Law "in his own words"