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Postings from October 2005
Guys, As mentioned on the list yesterday I started evaluating ffcall as a way of providing NCI functionality. http://www.haible.de/bruno/packages-ffcall.html I actually really like the current NCI implementation, although it suffers from a large nci.c file and all the usable prototypes need to be specified at compile time in call_list.txt. Over time as more libraries become supported this list will quickly grow. My main reason for visiting this is that I couldn't write the simple NCI example that I had in mind because callbacks are too restrictive, and unlikely to be fixable. I've now got a working POC for function calls, and although callbacks don't work yet, they're not far off. All but 11 of the 59 NCI tests pass, and those that don't work exercise callbacks or reading back values from types for which I haven't done yet. For those that want to try it, you'll of course need ffcall installed and rerun Configure. Being a Proof of Concept, I've hacked the '-l's for the libraries into the Makefile in the wrong place which means some of the other tests fail. For now, just try: perl -Ilib t/pmc/nci.t To recap the (mostly obvious) Pros & Cons. Pros: * Makes any prototype possible, not just those in call_list.txt * Probably won't initially make code much smaller, but would over time (stripped nci_ffcall.o & library is currently < 1/6 size of nci.o) * Callbacks can have any prototype as well, not just a data/user data pair * Callbacks no longer require user data to be managed by the 3rd party library (this is a biggy) * Callbacks will be able to support a return type Cons: * Reliance on a library, although NCI may be an optional feature * Performance? There are a few additional loops and switches, but I can't see this being a real issue * NCI would only be available on platforms which support the library we use; from what I've seen dynamic function calls is not easy to do cross-platform * Possibly incompatible 3rd party licensing To address some of the points in the Cons section, it would be possible to maintain multiple NCI backends, although more work. As far as PIR/PASM code, the interface is unchanged, although I would like to suggest that at some point the newclass signature include the return type in common with other opcodes, as hopefully we can support this. Cheers, Nick p.s. As you can see, I've been won over by ffcall, but I've only been using it for a day so there may well be show stoppers to using it.