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Posted to dev@tomcat.apache.org by bu...@apache.org on 2011/06/22 17:10:41 UTC

DO NOT REPLY [Bug 51417] New: Apache mod_jk worker gets stuck in OK/BUSY.

https://issues.apache.org/bugzilla/show_bug.cgi?id=51417

             Bug #: 51417
           Summary: Apache mod_jk worker gets stuck in OK/BUSY.
           Product: Tomcat Connectors
           Version: 1.2.31
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Common
        AssignedTo: dev@tomcat.apache.org
        ReportedBy: smendenh@redhat.com
    Classification: Unclassified


Created attachment 27193
  --> https://issues.apache.org/bugzilla/attachment.cgi?id=27193
busy.patch created by Mladen turn and verified independently to fix this issue

An AJP worker can get stuck in the OK/BUSY state and - in the case of a
stateless web service - not handle any further requests. 

In jk_lb_worker.c's service(), a worker is set to busy if it can't provide a
free endpoint. If a request is finished and releases one of the worker's
endpoints then the busy state is cleared. 

The problem is that as one thread performs the final jk_sleep() in
jk_ajp_common's do_ajp_service(), all endpoints for the worker may be released. 

Now the worker is marked busy, but no requests will complete subsequently which
would clear the busy state. The worker is stuck, indefinitely. 

The problem is fairly easy to reproduce as follows: 

- Configure an lb worker with a few AJP member workers. 
- Configure one of the AJP workers with connection_pool_size=1. 
- Run only the application servers corresponding to the worker with
connection_pool_size=1. 
- Deploy a servlet that sleeps for 200ms (default 2 retries * 100ms sleep). 
- Invoke the servlet twice in parallel, via Apache and mod_jk. 

The above is a pathological setup and just for testing, however it has been
encountered in a specific use case with a web service.

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DO NOT REPLY [Bug 51417] Apache mod_jk worker gets stuck in OK/BUSY.

Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=51417

--- Comment #2 from Mladen Turk <mt...@apache.org> 2011-06-22 16:40:31 UTC ---
Oops. Gave a wrong SVN reference. It's r1137200
http://svn.apache.org/viewvc?rev=1137200&view=rev

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DO NOT REPLY [Bug 51417] Apache mod_jk worker gets stuck in OK/BUSY.

Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=51417

Mladen Turk <mt...@apache.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED

--- Comment #1 from Mladen Turk <mt...@apache.org> 2011-06-22 16:37:40 UTC ---
The fix was applied to the trunk as r1137160
http://svn.apache.org/viewvc?view=revision&revision=1137160

Thanks for filling the issue with the better explanation of symptoms.
I tested the patch and it cleanly applies for all mod_jk versions from
1.2.27 up, so anyone affected with the bug can use the attached patch
until 1.2.32 gets released.

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DO NOT REPLY [Bug 51417] Apache mod_jk worker gets stuck in OK/BUSY.

Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=51417

Samuel Mendenhall <sm...@redhat.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #27193|0                           |1
           is patch|                            |
  Attachment #27193|application/octet-stream    |text/plain
          mime type|                            |
  Attachment #27193|busy.patch created by       |busy.patch created by
        description|Mladen turn and verified    |Mladen Turk and verified
                   |independently to fix this   |independently to fix this
                   |issue                       |issue

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