Affects Version/s: framework-4.2.1
Fix Version/s: framework-4.4.0
Environment:MacOS 10.7.5, java version "1.6.0_65", Java(TM) SE Runtime Environment (build 1.6.0_65-b14-462-11M4609), Java HotSpot(TM) 64-Bit Server VM (build 20.65-b04-462, mixed mode)
As discussed on the user list () there is a deadlock in Java 6 (if bug 4670071  is not fixed). The problem is the hidden, implicit ClassLoader.loadClassInternal which is is synchronized(this) in that case.
Consider the following scenario:
- bundle 2 wants to load a class of bundle 1 - hence is not synchronized with bundle 1's classloader - thus uses the m_classLocks locking mechanism to lock bundle 1's classloader for the particular class being loaded. Then calls defineClass (with bundle 1's classloader)
- before it can do so, bundle 1 wants to load the same class (of bundle 1) - hence does a synchronized loadClassInternal. then reaches the m_classLocks locking mechanism and notices that there's another thread loading the class
-> this results in the deadlock reported.
There's multiple fixes for this:
- use Java 7
- use -XX:+UnlockDiagnosticVMOptions -XX:+UnsyncloadClass
- create a special Java 6 classloader (Java 7 would use the current one) which does a plain synchronized findClass() - and replaces all synchronized(m_classLocks) with synchronized(this)