[undertow-dev] Unexpected RequestLimitingHandler behavior after queue gets full

[Stuart Douglas]

I created a JIRA:

https://issues.jboss.org/browse/UNDERTOW-349

Fix is upstream, will be in release of 1.1.2.Final and 1.2.0.Beta7. 

Stuart

----- Original Message -----
> From: "Piotr Betkier" <pbetkier at gmail.com>
> To: undertow-dev at lists.jboss.org
> Sent: Thursday, 4 December, 2014 9:12:25 AM
> Subject: [undertow-dev] Unexpected RequestLimitingHandler behavior after	queue gets full
> 
> Hello,
> 
> I wanted to introduce a constraint on the number of requests my server tries
> to handle at a time and played around with RequestLimitingHandler a little
> bit. However, I observed unexpected behavior once RequestLimit's queue gets
> full.
> 
> I've created a RequestLimitingHandler with both maximumConcurrentRequests and
> queueSize set to 1 and nextHandler that responds after a 3 second sleep.
> This is what I observed:
> 
> When I sent 2 concurrent requests with a curl, I got the first response after
> 3 seconds and the second one after 6 - just as expected, the second request
> got queued.
> 
> When I sent 3 concurrent requests, I got two correct responses and one 513 -
> just as expected, my third request couldn't fit into the queue so a failure
> handler got called.
> 
> Now it got tricky - this made RequestLimit enter an invalid state, where its
> "state" field got decremented below the value that represents 0 current
> requests. Now "state & MASK_CURRENT" gives 2147483647 instead of 0, so the
> next time I make a single request, RequestLimit thinks there are 2147483647
> requests in the system currently and queues my request instead of handling
> it. Then I make yet another request and now the queue is full, so 513 error
> is generated instantly which in turn makes RequestLimit poll my first
> pending request from the queue and dispatch it for handling. RequestLimit
> got corrupted and is unusable from now on.
> 
> I hope I explained my observations clearly. Is there something wrong in my
> setup, my understanding of Undertow or it's a bug? This is my code snippet,
> tested with undertow 1.1.0.Final and 1.2.0.Beta5:
> 
> import io.undertow.Undertow;
> import io.undertow.server.HttpHandler;
> import io.undertow.server.HttpServerExchange;
> import io.undertow.server.handlers.RequestLimitingHandler;
> import io.undertow.util.Headers;
> 
> public class Main {
> 
> public static void main(String[] args) {
> Undertow server = Undertow.builder()
> .addHttpListener(8080, "localhost")
> .setHandler(new RequestLimitingHandler(1, 1, handler()))
> .build();
> 
> server.start();
> }
> 
> private static HttpHandler handler() {
> return new HttpHandler() {
> @Override
> public void handleRequest(final HttpServerExchange exchange) throws Exception
> {
> Thread.sleep(3000);
> exchange.getResponseHeaders().put(Headers.CONTENT_TYPE, "text/plain");
> exchange.getResponseSender().send("Hello World");
> }
> };
> }
> 
> }
> 
> 
> Cheers,
> Piotr
> 
> 
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