https://issues.redhat.com/browse/WFLY-20430 reports a ThreadLocal leak as described below. We can see that OverridingClassFileLocator#close + SafeCacheProvider#remove are called to remove single classes at a time but clear is never called to remove all classes.

From https://hibernate.zulipchat.com/#narrow/channel/132094-hibernate-orm-dev/topic/WFLY-20430.20.2B.20leak.3F/near/503330528 :

“probably Enhancer needs expose a clear method that can be called from the EnhancingClassTransformerImpl
”

Note that EnhancingClassTransformerImpl does call bytecodeProvider.resetCaches()which might be a good place to call Enhancer#clear to clear all from the thread local.

Details of the thread local leak copied from WFLY-20430:

Class Name                                                                         | Referenced Objects | Shallow Heap | Ref. Shallow Heap | Retained Heap

org.jboss.threads.JBossThread @ 0xc78b9638  ServerService Thread Pool – 262 Thread|             23,051 |          128 |         1,844,080 |    19,866,856
'- threadLocals java.lang.ThreadLocal$ThreadLocalMap @ 0xcb724348                  |             23,051 |           24 |         1,844,080 |    19,866,560
   '- table java.lang.ThreadLocal$ThreadLocalMap$Entry[1024] @ 0xc9c995e8          |             23,051 |        4,112 |         1,844,080 |    19,866,536
      '- [66] java.lang.ThreadLocal$ThreadLocalMap$Entry @ 0xcc1c3680              |                215 |           32 |            17,200 |       183,128
         '- value java.util.HashMap @ 0xcc1c36a0                                   |                215 |           48 |            17,200 |       183,072
            '- table java.util.HashMap$Node[16] @ 0xcc1c36d0                       |                215 |           80 |            17,200 |       183,024
               |- [3] java.util.HashMap$Node @ 0xce1925f0                          |                151 |           32 |            12,080 |           128
               |- [11] java.util.HashMap$Node @ 0xce1902f8                         |                 36 |           32 |             2,880 |        33,048
               |- [6] java.util.HashMap$Node @ 0xcb707618                          |                 25 |           32 |             2,000 |        20,296
               |- [13] java.util.HashMap$Node @ 0xcc1c3720                         |                  3 |           32 |               240 |         3,008
               '- Total: 4 entries                                                 |                    |              |                   |              

Values for the ^ HashMap$Node entries:

Type|Name |Value

ref |next |null
ref |value|net.bytebuddy.pool.TypePool$Resolution$Simple @ 0xcb3665c8
ref |key  |org.jboss.as.test.integration.jpa.hhh18901.Department
int |hash |-1592475309

Type|Name |Value

ref |next |java.util.HashMap$Node @ 0xce192570
ref |value|net.bytebuddy.pool.TypePool$Resolution$Simple @ 0xce190380
ref |key  |org.jboss.as.test.integration.jpa.hhh18901.PartTimeEmployee
int |hash |-1974976725

Type|Name |Value

ref |next |null
ref |value|net.bytebuddy.pool.TypePool$Resolution$Simple @ 0xcb707698
ref |key  |org.jboss.as.test.integration.jpa.hhh18901.Employee
int |hash |587571174

Type|Name |Value

ref |next |null
ref |value|net.bytebuddy.pool.TypePool$Resolution$Simple @ 0xcc1c37a8
ref |key  |org.jboss.as.test.integration.jpa.hhh18901.AbstractPersonnel
int |hash |185882269