A patch was already created and applied for classpath/gcc 4.1. It needs to be backported to the 4.0 branch.
See http://gcc.gnu.org/ml/java/2005-09/msg00053.html -- Summary: [gcc 4.0 only] Deadlock in java.net.URLClassLoader Product: gcc Version: 4.0.3 Status: UNCONFIRMED Severity: normal Priority: P2 Component: libgcj AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: mark at gcc dot gnu dot org CC: gcc-bugs at gcc dot gnu dot org,java-prs at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24147