z2-Environment

The code in com.zfabrik.impl.resources.NamespaceImpl._getResourceHandleImplNonNull(String) may run into a concurrency situation, where a collected resource handle leads to a repeated tick() and invq adding and then invalidation of a concurrently just newly created resource.

Example¶

• Threads T1, T2.
• Resource name N

Flow:

1. T1: lookup for N returns value holder with null resource handle.
2. T1: Goes into looping = true
3. T1: leaves synchronized block
4. T2: runs tick() and enters synchronized block
5. T2: Creates and adds new resource handle
6. T2: leaves synchronized block
7. T1: enters synchronized block again
8. T1: finds that it is looping and the value holder for N is not in the invQ and hence puts it into invQ (although the resource handle is NOT null anymore!!!)
9. T1: invalidates the resource for N right away

Acceptance Criteria¶

• When looping for pending invalidations make sure not to accidentally consider a valid non-null handle as to be invalidated

Test Cases¶

• com.zfabrik.test.core.resources.tests.Invalidations.concurrentLookupOfCollectedResource: Concurrent lookup and GCing on weakly held resource.