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From "Filip Hanik (JIRA)" <j...@apache.org>
Subject [jira] Created: (AMQ-1993) Systems hang due to inability to timeout socket write operation
Date Mon, 03 Nov 2008 00:33:05 GMT
Systems hang due to inability to timeout socket write operation
---------------------------------------------------------------

                 Key: AMQ-1993
                 URL: https://issues.apache.org/activemq/browse/AMQ-1993
             Project: ActiveMQ
          Issue Type: Bug
          Components: Broker
    Affects Versions: 5.2.0, 5.1.0
         Environment: Unix (Solaris and Linux tested)
            Reporter: Filip Hanik
            Priority: Critical


the blocking Java Socket API doesn't have a timeout on socketWrite invocations.
This means, if a TCP session is dropped or terminated without RST or FIN packets, the operating
system it left to eventually time out the session. On the linux kernel this timeout usually
takes 15 to 30minutes. 

For this entire period, the AMQ server hangs, and producers and consumers are unable to use
a topic.

I have created two patches for this at the page:
http://www.hanik.com/covalent/amq/index.html

Let me show a bit more
---------------------------------
"ActiveMQ Transport: tcp:///X.YYY.XXX.ZZZZ:2011" daemon prio=10 tid=0x0000000055d39000 nid=0xc78
runnable [0x00000000447c9000..0x00000000447cac10]
   java.lang.Thread.State: RUNNABLE
	at java.net.SocketOutputStream.socketWrite0(Native Method)
	at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:92)

This is a thread stuck in blocking IO, and can be stuck for 30 minutes during the kernel TCP
retransmission attempts.
Unfortunately the thread dump is very misleading since the name of the thread, is not the
destination or even remotely related to the socket it is operating on.
To mend this, a very simple (and configurable) ThreadNameFilter has been suggested to the
patch, that appends the destination and helps the system administrator correctly identify
the client that is about to receive data. 

-----------------------------------
	at org.apache.activemq.broker.region.Topic.dispatch(Topic.java:581)
	at org.apache.activemq.broker.region.Topic.doMessageSend(Topic.java:421)
	- locked <0x00002aaaec155818> (a org.apache.activemq.broker.region.Topic)
	at org.apache.activemq.broker.region.Topic.send(Topic.java:363)
The lock being held at this issue unfortunately makes the entire Topic single threaded. 
When this lock is being held, no other clients (producers and consumers) can publish to/receive
from this topic.
And this lock can hold up to 30 minutes.
I consider solving this single threaded behavior a 'feature enhancement' that should be handled
separately from this bug. Because even if it is solved, threads still risk being stuck in
socketWrite0 for dropped connections that still appear to be established.

For this, I have implemented a socket timeout filter, based on a TransportFilter, this filter
only times out connections that are actually writing data.

The two patches are at:
http://www.hanik.com/covalent/amq/patch-1-threadname-filter.patch
http://www.hanik.com/covalent/amq/patch-3-tcp-writetimeout.patch

the binary 0000.jar applies to both 5.1 and trunk and can be used today in existing environments.





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