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: [email protected]
ReportedBy: [email protected]
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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