[GEODE-8671] Two threads calling get and retrieve the same PdxInstance, resulting in corruption

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.12.2, 1.13.2, 1.14.0, 1.15.0
• Component/s: regions
• Labels: blocks-1.14.0​ pull-request-available
• Assignee: Jianxia Chen
• Reporter: Dan Smith
• Created: 29/Oct/20 18:39
• Updated: 29/Mar/21 18:31
• Resolved: 04/Mar/21 09:12

Description

Even if copy-on-read is set to true, two threads calling get on a partitioned region can end up with the same PdxInstance object.

This is problematic because some PdxInstances methods are not thread safe. Although the underlying bytes are immutatable, the PDXInstance has a ByteSource with a position field that changes. That means two threads doing serialization or calling toString on the PdxInstance could result in one or more threads getting a corrupt read.

It looks like they are ending up with the same instance because of the behavior in LocalRegion.optimizedGetObject. We use futures to make sure there is only 1 get that goes through, and both threads receive the same value.

Ending up in optimizedGetObject requires a race with the put, because if the value was in the cache at the beginning of the get it would be returned earlier in the get process.

I put a test that reproduces this issue here - https://github.com/upthewaterspout/geode/pull/new/feature/pdx-instances-shared

Issue Links

• links to: GitHub Pull Request #5925