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Date: Fri, 5 Apr 2013 16:22:33 -0400
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 <CAGV1rDKeFU50_pGrtggvS_mZdsE97hvEoQxar0ri+Bp29+HLDw@mail.gmail.com>
Subject: Re: websockets holding on to threads.
From: "Howard W. Smith, Jr." <smithh032772@gmail.com>
To: Tomcat Users List <users@tomcat.apache.org>
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On Fri, Apr 5, 2013 at 9:07 AM, Anton Piatek1 <anton.piatek@uk.ibm.com>wrote:

> I am seeing what at first appears to be a bug, but given the lack of other
> reports I can't believe I am the only person seeing this, so maybe it is
> user-error.
>
> I have tomcat (was 7.0.30, but I just tried with 7.0.39) running a website
> which uses websockets. The websockets code in tomcat isn't that
> complicated - My servlet returns a new subclass of StreamInbound which has
> overridden the onTextData() and onBinaryData() methods. This seems to
> generally work fine, and I can send and receive data happily.
>
> However when I load up several browser windows I find that tomcat hangs. I
> used jconsole to check the tomcat threads and found that as I open each
> new websocket, the tomcat worker threads go from idle threads waiting for
> work to the following busy, blocking threads waiting for websocket data.
>
>
I have not written low-level websocket code as you are doing, but I think I
have seen this behavior even in/with my app, and others have reported and
discussed this issue in more ways than one.

I am using Atmosphere Framework via PrimeFaces Push to implement websockets
in my app, and it does work well with one browser tab/window, but it is
commonly reported that websockets do not work when one client (machine) has
multiple simultaneous websocket connections to the server.

Since I use Atmosphere Framework, I searched their google groups for the
following:

browser windows

and found the following (URL and quote from page at URL below):

https://github.com/Atmosphere/atmosphere/issues/493

According to HTTP RFC<http://www.w3.org/Protocols/rfc2616/rfc2616-sec8.html>
:

Clients that use persistent connections SHOULD limit the number of
simultaneous connections that they maintain to a given server. A
single-user client SHOULD NOT maintain more than 2 connections with any
server or proxy.

This can cause problems if you have multiple tabs/window open, which all
maintain a persistent connection. It would be great if persistent
connections should be shared (as GWT or Bayeux
Protocol<http://svn.cometd.com/trunk/bayeux/bayeux.htm> does
it).


> Name: http-bio-4415-exec-5
> State: RUNNABLE
> Total blocked: 50  Total waited: 112
>
> Stack trace:
> java.net.SocketInputStream.socketRead0(Native Method)
> java.net.SocketInputStream.read(SocketInputStream.java:161)
> java.net.SocketInputStream.read(SocketInputStream.java:132)
>
> org.apache.coyote.http11.upgrade.UpgradeBioProcessor.read(UpgradeBioProcessor.java:81)
> org.apache.catalina.websocket.WsFrame.nextFrame(WsFrame.java:214)
>
> org.apache.catalina.websocket.WsInputStream.nextFrame(WsInputStream.java:68)
> org.apache.catalina.websocket.StreamInbound.onData(StreamInbound.java:149)
>
> org.apache.coyote.http11.upgrade.UpgradeProcessor.upgradeDispatch(UpgradeProcessor.java:83)
>
> org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:587)
>
> org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
>    - locked org.apache.tomcat.util.net.SocketWrapper@ddb0d168
>
> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1156)
>
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:626)
> java.lang.Thread.run(Thread.java:780)
>
> I am trying to figure out what I am missing. I didn't think I needed to
> override StreamInbound.onData() in my class, but as that seems to be what
> is keeping the thread busy, presumably waiting for data looking at that
> stack.
>
> Am I misunderstanding something, or is this possibly a tomcat bug?
>

I don't think this is a tomcat bug, but I could be mistaking.


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> IBM United Kingdom Limited - Registered in England and Wales with number
> 741598.
> Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
>

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