PR gh-25038 introduced regressions in SimpleThreadScope and
SimpleTransactionScope in Spring Framework 5.2.7. Specifically, if a
thread-scoped or transaction-scoped bean has a dependency on another
thread-scoped or transaction-scoped bean, respectively, a
ConcurrentModificationException will be thrown on Java 11 or higher.
The reason is that Java 11 introduced a check for concurrent
modification in java.util.HashMap's computeIfAbsent() implementation,
and such a modification can occur when a thread-scoped bean is being
created in order to satisfy a dependency of another thread-scoped bean
that is currently being created.
This commit fixes these regressions by switching from HashMap to
ConcurrentHashMap for the instance maps in SimpleThreadScope and
SimpleTransactionScope.
Closes gh-25618
148dc95eb1