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