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Posted to dev@tomcat.apache.org by bu...@apache.org on 2014/03/23 07:11:07 UTC
[Bug 56304] New: WebSocket send locks and timeout does not occur
after 20 seconds
https://issues.apache.org/bugzilla/show_bug.cgi?id=56304
Bug ID: 56304
Summary: WebSocket send locks and timeout does not occur after
20 seconds
Product: Tomcat 7
Version: 7.0.52
Hardware: PC
OS: Linux
Status: NEW
Severity: major
Priority: P2
Component: Catalina
Assignee: dev@tomcat.apache.org
Reporter: rstoyanchev@yahoo.com
Created attachment 31429
--> https://issues.apache.org/bugzilla/attachment.cgi?id=31429&action=edit
Extract from thread dump
Start a WebSocket server on one computer.
Connect from aonther using a browser.
Starts sending messages from server to client periodically.
Turn off wifi or unplug network cable on client side. Initially Tomcat appears
to be sending messages but eventually one of the sends hangs indefinitely.
The 20 second timeout as documented on the WebSocket FAQ does not occur and
attempts to close the WebSocket session from another thread also locks that
thread as well.
If you now turn the wifi back on or plug the network cable, at last the two
threads that are stuck are released and the WebSocket handler gets a
notification of the session closing.
In the attachment, the first two stack traces are of (1) the thread trying to
send and (2) the thread that attempted to close. The 3rd stack trace is of
another hung thread.
NOTE that this does not occur on Tomcat 8 where the timout does occur and also
attempts to close a session do succeed.
Also I am told that the timeout does occur on Windows but I haven't verified it
myself. I am using Linux.
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[Bug 56304] WebSocket send locks and timeout does not occur after 20
seconds
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=56304
--- Comment #5 from rstoyanchev@yahoo.com ---
Thanks, when you say it's expected to work this way, does it also mean the send
timeout cannot be enforced with the BIO connector?
Can anything meaningful be done if an application can detect a timeout
situation? Currently trying to close the session from another thread locks up
that thread too.
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[Bug 56304] WebSocket send locks and timeout does not occur after 20
seconds
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=56304
--- Comment #2 from rstoyanchev@yahoo.com ---
The reference to Windows is for the server.
I am using default server configuration on both Tomcat 7 and 8 so I guess that
probably accounts for the different behavior. I can try Tomcat 7 with NIO
connector to confirm what the behavior is.
That said is the BLOCKING_SEND_TIMEOUT property not supported with default
Tomcat 7 configuration? This is not reflected in the WebSocket FAQ.
Also should an attempt to close the session from a separate thread block as
well? It would be difficult then (or rather not possible) for an application
not to lose two threads to a client that disconnected abnormally.
If that is indeed the case then perhaps it should probably be recommended
prominently in the FAQ to switch to the NIO connector if using Tomcat 7 with
WebSockets.
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[Bug 56304] WebSocket send locks and timeout does not occur after 20
seconds
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=56304
--- Comment #7 from rstoyanchev@yahoo.com ---
I guess that makes the combination of WebSocket and BIO pretty unusable. Good
to know in any case. I have to double check the behavior with Servlet 3 async
in the same scenario with NIO.
BTW while you're in the FAQ, it says that the buffer size limit is for incoming
messages. However an exception is raised also when trying to send messages
larger than 8K. I suspect it is an issue with the FAQ?
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[Bug 56304] WebSocket send locks and timeout does not occur after 20
seconds
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=56304
--- Comment #8 from Mark Thomas <ma...@apache.org> ---
If you have an issue sending more than 8k then that is a separate question for
the users mailing list. Tomcat imposes no such limitation as it has no need to
buffer then entire message.
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[Bug 56304] WebSocket send locks and timeout does not occur after 20
seconds
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=56304
--- Comment #4 from Mark Thomas <ma...@apache.org> ---
Add info from the users list that the timeout does occur after approx 15
minutes.
This is - believe it or not - working as designed! See this thread from SO (it
is off topic for SO but spot on for this problem)
http://stackoverflow.com/questions/15484906/change-the-tcp-timeout-for-a-linux-network-device
It would appear that the only way to handle this if you want to continue to use
the BIO connector is is to reduce /proc/sys/net/ipv4/tcp_retries2
I'll add some information about this to the WebSocket docs.
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[Bug 56304] WebSocket send locks and timeout does not occur after 20
seconds
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=56304
--- Comment #9 from rstoyanchev@yahoo.com ---
Okay thanks Mark.
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[Bug 56304] WebSocket send locks and timeout does not occur after 20
seconds
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=56304
Mark Thomas <ma...@apache.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |FIXED
--- Comment #6 from Mark Thomas <ma...@apache.org> ---
There is no Java API available for setting a write timeout.
Closing the socket may or may not be possible - it depends on the locking
implemented by the JRE. I've taken a look at the Java side and there is a lock
on close but not on write. However, a lock could occur on the same object in
the native code.
Given your experience, it looks like tweaking the kernel network parameters are
the best (only?) option if you want to run WebSocket + HTTP BIO + Linux.
I have added some appropriate notes to the WebSocket docs for 8.0.x (8.0.5+)
and 7.0.x (7.0.53+)
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[Bug 56304] WebSocket send locks and timeout does not occur after 20
seconds
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=56304
--- Comment #1 from Mark Thomas <ma...@apache.org> ---
Are you sure you used the same connector on Tomcat 7 and Tomcat 8? The default
connector on Tomcat 7 is BIO whereas it is NIO on Tomcat 8.
When you refer to Windows or Linux is that client side, server side or both?
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[Bug 56304] WebSocket send locks and timeout does not occur after 20
seconds
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=56304
--- Comment #3 from Mark Thomas <ma...@apache.org> ---
For the record, I can reproduce this with 8.0.x using:
- Unbuntu 12.04.04 LTS VM as the server (fully patched)
- Latest 8.0.x code
- Oracle 1.7.0_45 64-bit JVM
- Snake WebSocket example
- Firefox on OSX (fully patched) as the client
Simply turning off the WiFi on the OSX client leads to a read thread
(http-bio-8080-exec-NN) and a write thread (SnakeTimer) blocking indefinitely.
I'm looking into what can be done about this now.
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