Java "ports" and OutPort

[Erik Pearson]

Hi,

I'm hooking Kawa into an existing servlet that also runs Jacl. So far, the 
experience is very impressive!

Kawa needs to coexist as part of a web pages template processor which 
writes html or Jacl output to the servlet response stream independently of 
Kawa. I'm finding some strange side-effects of the OutPort class, mainly, I 
believe, having to do with the usage of PrintWriter as the base classs.

For instance, since OutPort/PrintWriter seems to buffer independently of 
the underlying stream it is possible to write to the PrintWriter first 
(e.g. via Kawa), then write through the OutputStream via Jacl (or java) and 
find that the second write appears in the stream first. In fact, if output 
is not forced with a (newline myport) then nothing indeed may be output at 
all.

Now some of this can be solved by the servlet handling the response port 
interaction with Kawa a little smarter (like flushing the port after all 
the scheme-ing is done). However, the main issue, I think, is that there 
should be some way of making display, write, etc. atomic in relation to 
getting the output through to the underlying stream. A simple flush at the 
end of each call would be sufficient.

However, to support more efficient sequences of output, it would also be 
good to be able to control flushing behavior (i.e. flush at end of call or 
not).

So one question is -- what would be the best method of controlling this?

Some suggestions are...

A top-level variable which the output functions look at? E.g. 
output-flush-per-call with #t and #f

A field of the output port that can be controlled and queried via a couple 
of functions.

A keyword option for each output function to determine the desired behavior

(display "blah blah" myport flush: #t)


I will need to make this change for myself, for practical purposes, in some 
form or fashion. Would this be a candidate for folding back into the 
codebase? Is it something that, assuming it is a good idea, Per would 
rather do at the core level and I pick up from CVS? (Assuming something 
like this is not already in the pipeline).

Thanks!

Erik Pearson.