From mboxrd@z Thu Jan  1 00:00:00 1970
To: 9fans@cse.psu.edu
Subject: Re: [9fans] vfork and paging
From: rog@vitanuova.com
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Date: Thu,  4 Oct 2001 15:09:00 +0100
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> There are (at least) two libraries providing CSP-style channels for Java:
>
>   http://www.cs.ukc.ac.uk/projects/ofa/jcsp
>   http://www.rt.el.utwente.nl/javapp/

and they both (well, especially jcsp) look substantially more complex
(and awkward) than the plan 9 threads library, let alone Limbo...

i took a simple example from CTJ and wondered what it looked like
under the various systems:

Limbo:
	for (i := 0; i < 20; i++) {
		alt {
		n := <-inChannel[0] =>
			... do something with n
		n := <-inChannel[1] =>
			... do something with n
		}
	}

Plan 9:
	int i, n;
	Alt alts[3];
	alts[0].c = inChannel[0];
	alts[0].v = &n;
	alts[0].op = CHANRCV;
	alts[1].c = inChannel[1];
	alts[1].v = &n;
	alts[1].op = CHANRCV;
	alts[2].op = CHANEND;

	for (i = 0; i < 20; i++) {
		switch(alt(alts)) {
		case 0:
			... do something with n
			break;
		case 1:
			... do something with n
			break;
		}
	}

CTJ:
	Integer n = new Integer(); // n is an Object
	Process alt = new Alternative(new Guard[] {
		new Guard(inChannel[0], new Process() {
			public void run() {
				inChannel[0].read(n);
				... do something with n
			}
		}),
		new Guard(inChannel[1], new Process() {
			public void run() {
				inChannel[1].read(n);
				... do something with n
			}
		})
	};
	for (int i=0; i<20; i++) {
		alt.run();
	}


JCSP:
	i couldn't quickly work out how to do it with jcsp.
	it has about 40 classes just for the basic primitives...
	the plan 9 thread library has 38 functions *in total*.

basically, when it comes down to it, there's no substitute for decent
language-level primitives.  though it's nice to see there are others
around that acknowledge the inadequacies of the conventional
schemes...

  rog.