Tim Peters writes:
I'm not a fan of continuations myself; coroutines can be implemented faithfully via threads (I posted a rather complete set of Python classes for that in the pre-DejaNews days, a bit more flexible than Icon's coroutines); and:
Continuations are more powerful than coroutines, though I admit they're a bit esoteric. I programmed in Scheme for years without seeing the need for them. But when you need 'em, you *really* need 'em. No way around it. For my purposes (massively scalable single-process servers and clients) threads don't cut it... for example I have a mailing-list exploder that juggles up to 2048 simultaneous SMTP connections. I think it can go higher - I've tested select() on FreeBSD with 16,000 file descriptors. [...] BTW, I have actually made progress borrowing a bit of code from SCM. It uses the stack-copying technique, along with setjmp/longjmp. It's too ugly and unportable to be a real candidate for inclusion in Official Python. [i.e., if it could be made to work it should be considered a stopgap measure for the desperate]. I haven't tested it thoroughly, but I have successfully saved and invoked (and reinvoked) a continuation. Caveat: I have to turn off Py_DECREF in order to keep it from crashing. | >>> import callcc | >>> saved = None | >>> def thing(n): | ... if n == 2: | ... global saved | ... saved = callcc.new() | ... print 'n==',n | ... if n == 0: | ... print 'Done!' | ... else: | ... thing (n-1) | ... | >>> thing (5) | n== 5 | n== 4 | n== 3 | n== 2 | n== 1 | n== 0 | Done! | >>> saved | <Continuation object at 80d30d0> | >>> saved.throw (0) | n== 2 | n== 1 | n== 0 | Done! | >>> saved.throw (0) | n== 2 | n== 1 | n== 0 | Done! | >>> I will probably not be able to work on this for a while (baby due any day now), so anyone is welcome to dive right in. I don't have much experience wading through gdb tracking down reference bugs, I'm hoping a brave soul will pick up where I left off. 8^) http://www.nightmare.com/stuff/python-callcc.tar.gz ftp://www.nightmare.com/stuff/python-callcc.tar.gz -Sam