On Oct 24, 2012, at 3:09 PM, Richard D. Morey wrote:
> On 24/10/12 8:53 PM, Simon Urbanek wrote:
>> 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.
> How can I start a new thread? By running R again from the command line, or is
> there a better way?
>
No, you have to use the system thread API like pthreads, NSThread etc. If you
have to ask about this, you probably don't want to go there ;) - threads can be
quite dangerous if you are not familiar with them.
Another poor man's solution is to simply have your C code write out a file with
the progress. Along the same lines you could use a shared object to store the
progress (e.g. via bigmemory) ...
>> 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.
> I do use R_CheckUserInterrupt(), but if I understand what you're saying then
> given that it doesn't work, httpd must not run during the interrupt check. At
> least, on OSX, which is what I'm testing on.
>
Yes, if your code calls R_CheckUserInterrupt() and httpd doesn't respond at
that point then it may not be allowed to run. On OS X you can try your luck
with R_ProcessEvents() as well.
Cheers,
Simon
>> 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?
>>>
>>> ______________________________________________
>>> R-devel@r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>>
>>>
>
>
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