ClassNotFoundException can occur when using parallel deployments

[edwardsmatt]

Background:
• Tomcat Parallel Deployments are in use
• The session object contains a custom data type only available on the web-application class-path
• Requests are occurring whilst the application is being redeployed
• Hazelcast is configured to use non-sticky sessions and deferred write.

Description:
When using parallel deployments whilst an application is processing requests, a new deployment can trigger a class not found exception in the HazelcastSession deserializeMap method. I believe this is because the web-application classpath has begun to unload whilst the session manager runs in the tomcat common classloader.

Impact:
Once Tomcat has entered this state, the instance becomes unstable and will only respond with a 500 - InternalServerError until the tomcat instance is restarted.

More Details

An example to reproduce can be found here: https://github.com/edwardsmatt/hazelcast-cnfe-parallel-deployment-example.