On Oct 24, 2012, at 2:13 PM, Richard D. Morey wrote:
> 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
>
You can't. R doesn't support threading so it's simply not possible to have an
asynchronous eval. The R HTTP server works by simply enqueuing an eval to run
while R is idle, it can't do that if R is busy. (Note that the HTTP server was
*only* designed for the internal help).
What you can do is have your C code start another thread that reports the
progress when asked e.g. on a socket, but that thread is not allowed to call
any R API so you want that progress to be entirely in your C code.
Note that if your C code is robust enough, it can call R_CheckUserInterrupt()
to allow external events to happen, but a) your C code must in that case be
prepared for early termination (clean up memory etc.) and b) I don't remember
if the httpd is allowed to run during interrupt check on all platforms - you
may want to check that first.
Cheers,
Simon
> 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?
>
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>
>
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