Scott Dillard wrote:
Thanks for the response guys.
I'm still curious as to the specific mechanism by which a strictly
compile-time function affects the run-time behavior of the GC. Bulat
says that touch# makes the runtime aware that the fptr object is still
in use, but how does it do this if, at runtime, it doesn't do
anything? Does if affect the scheduling of collections? Does it mark
the fptr object with some flag when its allocated? What if, for
example, if I put the touch# behind a branch that is conditional on
run-time values? How would this affect things?
It's not as complicated as you think. touch# takes a single argument, and
does nothing with it; it's only purpose is to ensure that the value passed
as its argument is "alive" as far as the rest of the compiler and runtime
is concerned.
There's no special mechanism at work here: touch# is just like an ordinary
IO operation, except that its implementation is empty, and the compiler
cannot use this fact for optimisation purposes. The compiler therefore
arranges that the argument to touch# is available, just as it would for any
other function.
Cheers,
Simon
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