[Opensim-dev] Is it OK performance-wise to long-poll a money module?

[Justin Clark-Casey]

I also used a long poll technique to integrate a webpage user interface for water-resource usage game work I did with 
Intel and Sandia National Labs a while back.  This made the webpage long pull for updates from OpenSimulator so that 
actions done by a player in-world (such as clicking on a water-using crop) would be received by javascript on the 
webpage and acted on appropriately (in this case by changing the webpage tab to the crop information page).  This was to 
get around the limitations of in-world user interfaces (MOAP on a hud wasn't working back then).

The code is at [1] if an example would be useful.  The polling is done by getUpdate() in [2] and the simulator sets up 
and initially handles a webservice call at [3], using JSON as the data transport.  When I get some spare time I'm going 
to write some blog posts about its technical aspects.

I didn't find any issue with timeouts - I found that the javascript could poll indefinitely.

[1] https://github.com/justincc/waterwars
[2] https://github.com/justincc/waterwars/blob/master/web/waterwars/js/waterwars/waterwars.js
[3] https://github.com/justincc/waterwars/blob/master/src/WaterWars/WebServices/ViewerWebServices.cs

On 15/09/12 10:53, Dahlia Trimble wrote:
> I've had excellent luck serving many simultaneous long-poll requests with the HTTP server that comes with OpenSimulator.
> Bear in mind though that each active request may consume a thread so you might need to increase available threads if you
> see problems. I'm not certain if the request threads are managed by the threadpool in OpenSimulator or if they are
> direct calls into .NET framework. I did search through the code once and found many threads that were not treadpool
> managed but I can't remember if HTTP threads were or not.
>
>
> On Fri, Sep 14, 2012 at 9:07 PM, Edmund Edgar <ed at avatarclassroom.com <mailto:ed at avatarclassroom.com>> wrote:
>
>     I've got a situation with the money module I'm working on where I'd
>     like an external program (running on the client PC in parallel to the
>     viewer) to be able to be in almost constant contact with the server
>     while the user is logged in. (I want it to be able to find out
>     whenever the user wanted to buy something.)
>
>     I figure I can do this by having the external program long-poll the
>     OpenSim server. (The external program makes a request, the server
>     waits such time as it has something to tell the external program, then
>     responds. It gives up and responds if there's nothing to say after 30
>     seconds or so, at which point the external program will make a new
>     request and start the cycle again.)
>
>     At this point if I was serving a web application with Apache I'd start
>     worrying that I was hogging a bunch of threads and eating through the
>     memory. Is this the kind of thing I should be worrying about with
>     OpenSim, or can I merrily go ahead and long-poll without worrying?
>
>     The kind of thing I'm thinking of follows:
>
>
>     public void FirstRegionLoaded ()
>
>              MainServer.Instance.AddHTTPHandler ("/checkfortransactions/",
>     CheckForTransactions);
>
>     }
>
>     public Hashtable CheckForTransactions(Hashtable request) {
>
>              UUID userUUID = (get a user id using a session ID passed in the
>     request or something);
>
>              int i;
>              // poll for 30 seconds then give up
>              for (i=0; i<30; i++) {
>                      if (m_transactionsAwaitingNotification.containsKey("userUUID")) {
>                              // Reply to the request
>                              Hashtable reply = new Hashtable ();
>                              reply["int_response_code"] = 200;
>                              reply["str_response_string"] = "{ Some JSON goes here }";
>                              reply["content_type"] = "text/json";
>                              return reply;
>                      }
>                      Thread.Sleep (1000);
>              }
>
>              Hashtable reply = new Hashtable ();
>              reply["int_response_code"] = 204; // No Content
>              return reply;
>
>              // The client will get this reply then hit /checkfortransactions/ again.
>
>     }
>
>     PS. Thanks for the replies to my C#-ignorant questions on previous threads.
>
>     --
>     Edmund Edgar
>     Avatar Classroom
>     Your classroom, on the web, in a virtual world.
>
>     ed at avatarclassroom.com <mailto:ed at avatarclassroom.com>
>     +81 090 3912 3380 <tel:%2B81%20090%203912%203380>
>     Skype: edmundedgar
>     Second Life: Edmund Earp
>     Linked In: edmundedgar
>     Twitter: @edmundedgar
>     http://www.avatarclassroom.com
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-- 
Justin Clark-Casey (justincc)
OSVW Consulting
http://justincc.org
http://twitter.com/justincc