Two or more threads hold one lock on an instance of java.util.Collections$SynchronizedMap and attempt to obtain a lock on a different instance (e.g. locks on 0x00000001d0d08bd8 and 0x00000001cea22628 in the example below) "thread-one" ... java.lang.Thread.State: BLOCKED (on object monitor) at java.util.Collections$SynchronizedMap.get(Collections.java:2584) waiting to lock <0x00000001cea22628> (a java.util.Collections$SynchronizedMap) at java.util.AbstractMap.equals(AbstractMap.java:495) at java.util.Collections$SynchronizedMap.equals(Collections.java:2631) locked <0x00000001d0d08bd8> (a java.util.Collections$SynchronizedMap) at org.jboss.jca.adapters.jdbc.xa.XAManagedConnectionFactory.isEqual(XAManagedConnectionFactory.java:563) locked <0x00000001d0d08bd8> (a java.util.Collections$SynchronizedMap) at org.jboss.jca.adapters.jdbc.xa.XAManagedConnectionFactory.equals(XAManagedConnectionFactory.java:598) at org.jboss.jca.adapters.jdbc.BaseWrapperManagedConnectionFactory$SubjectActions.doCheck(BaseWrapperManagedConnectionFactory.java:1397) at org.jboss.jca.adapters.jdbc.BaseWrapperManagedConnectionFactory$SubjectActions.addMatchingProperties(BaseWrapperManagedConnectionFactory.java:1508) at org.jboss.jca.adapters.jdbc.BaseWrapperManagedConnectionFactory.getConnectionProperties(BaseWrapperManagedConnectionFactory.java:1135) at org.jboss.jca.adapters.jdbc.xa.XAManagedConnectionFactory.matchManagedConnections(XAManagedConnectionFactory.java:533) ... at org.jboss.jca.adapters.jdbc.WrapperDataSource.getConnection(WrapperDataSource.java:138) at org.jboss.as.connector.subsystems.datasources.WildFlyDataSource.getConnection(WildFlyDataSource.java:66) ... "thread-two" ... java.lang.Thread.State: BLOCKED (on object monitor) at java.util.Collections$SynchronizedMap.size(Collections.java:2572) waiting to lock <0x00000001d0d08bd8> (a java.util.Collections$SynchronizedMap) at java.util.AbstractMap.equals(AbstractMap.java:482) at java.util.Collections$SynchronizedMap.equals(Collections.java:2631) locked <0x00000001cea22628> (a java.util.Collections$SynchronizedMap) at org.jboss.jca.adapters.jdbc.xa.XAManagedConnectionFactory.isEqual(XAManagedConnectionFactory.java:563) locked <0x00000001cea22628> (a java.util.Collections$SynchronizedMap) at org.jboss.jca.adapters.jdbc.xa.XAManagedConnectionFactory.equals(XAManagedConnectionFactory.java:598) ... [same stack as thread-one above] ... at org.jboss.jca.adapters.jdbc.WrapperDataSource.getConnection(WrapperDataSource.java:138) at org.jboss.as.connector.subsystems.datasources.WildFlyDataSource.getConnection(WildFlyDataSource.java:66) ...