Re: [9fans] critique of sockets API

[Eris Discordia <eris.discordia@gmail.com>]

> i don't think i understand what you're getting at.
> it could be that the blog was getting at the fact that select
> funnels a bunch of independent i/o down to one process.
> it's an effective technique when (a) threads are not available
> and (b) processing is very fast.

This might help: what he is getting at is probably the question of why not
make possible network applications that consist of a bunch of callbacks or
a mix of callbacks and listener/worker threads. Windows implements both
synchronous and asynchronous I/O. Threads are available. Callbacks, too, as
well as message queues. Ideally, it is the programmer's informed choice
based on their understanding of their application's priorities whether to
use callbacks, listener/worker threads, message queues, or a combination.
Someone may find it worth the effort to compare these approaches on a
platform that provides both. (COM is notorious for implementing things
through callback that get some wrapping of one's head around them before
making sense.)

--On Tuesday, June 09, 2009 20:07 -0400 erik quanstrom
<quanstro@quanstro.net> wrote:

> On Tue Jun  9 19:22:39 EDT 2009, bpisupat@cs.indiana.edu wrote:
>> Well, select() or alt might or might not be required depending on
>> whether  you want your thread to wait till the read operation waiting
>> for data from the network completes.
>
> your thread will always wait until any system call completes;
> they're all synchronous all the time.  if you want your application
> to do something else at the same time, you're going to need two
> threads and a synch device (like a lock + shared memory or a channel).
>
>> read()->process()->read()... alternating sequence of operations that is
>> required, wherein the application has to explicitly go fetch data from
>> the network  using the read operation. To borrow text from the paper:
>> <snip>
>> The API does not provide the programmer a way in which to say, "Whenever
>> there is data for me, call me to process it directly."
>> </snip>
>
> i don't think i understand what you're getting at.
> it could be that the blog was getting at the fact that select
> funnels a bunch of independent i/o down to one process.
> it's an effective technique when (a) threads are not available
> and (b) processing is very fast.
>
> perhaps you think this is doging the question, but the cannonical
> plan 9 approach to this is to note that it's easy (trivial) to have a n
> reader threads and m worker threads s.t. i/o threads don't block
> unless (a) there's nothing to i/o, or (b) the workers aren't draining
> the queue fast enough; and s.t. worker threads don't block
> unless (a) the i/o threads can't keep up.  in this case, there is no
> work to do anyway.  consider these two types of threads;
> let mb be a pointer to a message buffer.
>
> thread type 1
> 	for(;;)
> 		mb <- freechan
> 		read(fd, mb->wp, BUFSIZE);
> 		mb -> fullchan
> thread type 2;
> 	for(;;)
> 		mb <- fullchan
> 		do stuff
> 		mb -> freechan
>
> if your server issues responses, it's easy to add thread type 3.
>
> as you can see, this is a simple generalization of your case.  (if we
> have a queue depth of 0 and one thread 1 and one thread 2,
> we will get your loop.)  yet there should be no waiting.
>
>> The question was meant to ask as to how easy it is to programmatically
>> use the filesystem interface in a multi home network. But I agree that
>> support for  multiple network interfaces in Plan9 is way superior.
>
> i think the answer to your question is that programs don't care.
> programs that take a cannonical network address are just as
> happy to accept /net/tcp!www.example.com!http as they are to
> accept /net.alt/tcp!www.example.com!http.  for a short while
> i ran a 10gbit network on /net.10g.
>
> - erik
>