Re: [9fans] python csp

[roger peppe <rogpeppe@gmail.com>]

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2009/3/12 John Barham <jbarham@gmail.com>:
>>> How about using queues (http://docs.python.org/library/queue.html)?
>>
>> no alt.
>
> Couldn't you implement it approximately using
> http://docs.python.org/library/queue.html#Queue.Queue.qsize?

no. "approximately" in this case would mean "wrong".

for the time being, as i'm limited on time, i'm using pycsp
with a very slim wrapper around it to make its interface
palatable. it'll all be hideously inefficient, but i'm not
too concerned about that currently. i've attached it in case
anyone's interested.

joel: multiple readers and writers isn't the same thing as alt
at all - you need to be able to read from more than
one channel at once. sharing a single channel between
several processes doesn't get you that (although it's
great to have, and the plan9/inferno channel model
supports it)

  rog.

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import pycsp

Channel = pycsp.Channel

def chan(*n):
	'''Create a channel. If an argument is given, it specifies
	the buffer size (default 0, unbuffered)'''
	if len(n) == 0:
		n = 0
	else:
		n = n[0]
	if n > 0:
		c = pycsp.BufferedAny2OneChannel(buffer = pycsp.FifoBuffer(n))
	else:
		c = pycsp.Any2OneChannel();
	return c;

def alt(*cs):
	'''alt(chan....)
	Alt waits until one of the channels becomes ready for reading,
	then returns its read member - it is up to the caller
	to do the read'''
	return pycsp.Alternative(*map(lambda c: c.read, cs)).select();

def altf(*cs):
	'''altf(chan..., fn, chan..., fn, ...)
	Altf waits until one of the channels is ready for reading,
	then reads from it, calls its associated function,
	and returns the result of that call.'''

	as = []
	fs = []
	i = 0
	while i < len(cs):
		j = i
		while isinstance(cs[j], Channel):
			j = j + 1
		if i == j:
			raise 'expected channel(s)'
		f = cs[j]
		k = i
		while k < j:
			as.append(cs[k].read)
			fs.append(f)
			k = k + 1
		i = j + 1
	a = pycsp.Alternative(*as)
	s = a.select()
	i = 0
	while i < len(as):
		if s == as[i]:
			return fs[i](s())
		i = i + 1

def spawn(f, *args, **kwargs):
	pycsp.Process(f, *args, **kwargs).start();