From r.d.morey at rug.nl  Wed Oct 24 20:13:21 2012
From: r.d.morey at rug.nl (Richard D. Morey)
Date: Wed, 24 Oct 2012 20:13:21 +0200
Subject: [Rd] concurrent requests (Rook,
	but I think the question is more general)
Message-ID: <50882FC1.40608@rug.nl>

This question involves Rook, but I think the answer will be general 
enough that it pays to post here. At any rate, I don't know enough to 
know whether this is a Rook only issue or a general R issue.

Here's what I'd like to do (and indeed, have code that should do this):

1. Start R, Rook
2. Start an analysis via a HTTP request to Rook. This analysis uses 
.Call() to some compiled C code, if that matters. The C code calls a 
callback function to update a variable with its progress.
3. While the analysis is happening, use Rook to obtain current status 
with an HTTP request

The problem is that once the analysis starts, Rook does not respond to 
requests. All of the status requests to Rook pile up, and then are 
answered when the analysis (step 2) is done. Here is some example code 
to demonstrate what the issue:

##########

library(Rook)
s <- Rhttpd$new()
s$add(
   name="pingpong",
   app=Rook::URLMap$new(
     '/ping' = function(env){
       req <- Rook::Request$new(env)
       res <- Rook::Response$new()
       res$write('This is ping.')
       Sys.sleep(20)
       res$finish()
     },
     '/pong' = function(env){
       req <- Rook::Request$new(env)
       res <- Rook::Response$new()
       res$write("This is pong.")
       res$finish()
     },
     '/?' = function(env){
       req <- Rook::Request$new(env)
       res <- Rook::Response$new()
       res$redirect(req$to_url('/pong'))
       res$finish()
     }
   )
)

s$start(quiet=TRUE)
s$browse('pingpong')

#############################

If you request /ping, R runs Sys.sleep() for 20 seconds. This is where 
my .Call() statement would be. While the .Call() (Sys.sleep()) function 
is doing its thing, I need to get Rook to respond on /pong (which would 
simply respond with the progress), but if you run this code, request 
/ping, then immediately request /pong, you'll see that the /pong request 
will not be answered until the Sys.sleep() is done.

Of course, for a progress report to be useful, the requests have to be 
answered immediately. Is this a Rook issue, or an R issue? Or am I 
asking something unreasonable?



[Rd] concurrent requests (Rook, but I think the question is more general)
Richard D. Morey