Found one Java-level deadlock:
=============================
"exec_null_1":
  waiting to lock monitor 0x08084938 (object 0x73dac270, a org.apache.tools.ant.Project),
  which is held by "AWT-XAWT"
"AWT-XAWT":
  waiting to lock monitor 0x0808499c (object 0x72652190, a java.lang.Object),
  which is held by "exec_null_1"

Java stack information for the threads listed above:
===================================================
"exec_null_1":
	at org.apache.tools.ant.Project.fireMessageLoggedEvent(Project.java:2149)
	- waiting to lock <0x73dac270> (a org.apache.tools.ant.Project)
	at org.apache.tools.ant.Project.fireMessageLogged(Project.java:2271)
	at org.apache.tools.ant.Project.log(Project.java:449)
	at org.apache.tools.ant.Task.log(Task.java:294)
	at net.sourceforge.pmd.util.AntLogHandler.publish(AntLogHandler.java:45)
	at java.util.logging.Logger.log(Logger.java:472)
	at java.util.logging.Logger.doLog(Logger.java:494)
	at java.util.logging.Logger.log(Logger.java:517)
	at java.util.logging.Logger.fine(Logger.java:1068)
	at org.openide.util.Task.notifyRunning(Task.java:197)
	- locked <0x70a67d40> (a org.openide.util.RequestProcessor$Task)
	at org.openide.util.RequestProcessor$Task.schedule(RequestProcessor.java:608)
	- locked <0x72652190> (a java.lang.Object)
	at org.openide.util.RequestProcessor.post(RequestProcessor.java:279)
	at org.openide.util.RequestProcessor.post(RequestProcessor.java:250)
	at org.apache.tools.ant.module.bridge.impl.BridgeImpl.run(BridgeImpl.java:300)
	at org.apache.tools.ant.module.run.TargetExecutor.run(TargetExecutor.java:460)
	- locked <0x73c905f0> (a org.apache.tools.ant.module.run.TargetExecutor)
	at org.netbeans.core.execution.RunClassThread.run(RunClassThread.java:151)
"AWT-XAWT":
	at org.openide.util.RequestProcessor$Task.schedule(RequestProcessor.java:607)
	- waiting to lock <0x72652190> (a java.lang.Object)
	at org.apache.tools.ant.module.bridge.impl.NbBuildLogger.checkForStop(NbBuildLogger.java:188)
	at org.apache.tools.ant.module.bridge.impl.NbBuildLogger.messageLogged(NbBuildLogger.java:578)
	at org.apache.tools.ant.Project.fireMessageLoggedEvent(Project.java:2171)
	- locked <0x73dac270> (a org.apache.tools.ant.Project)
	at org.apache.tools.ant.Project.fireMessageLogged(Project.java:2271)
	at org.apache.tools.ant.Project.log(Project.java:449)
	at org.apache.tools.ant.Task.log(Task.java:294)
	at net.sourceforge.pmd.util.AntLogHandler.publish(AntLogHandler.java:45)
	at java.util.logging.Logger.log(Logger.java:472)
	at java.util.logging.Logger.doLog(Logger.java:494)
	at java.util.logging.Logger.log(Logger.java:517)
	at java.util.logging.Logger.finest(Logger.java:1100)
	at sun.awt.X11.XMappingEvent.get_send_event(XMappingEvent.java:44)
	at sun.awt.X11.XMappingEvent.getFieldsAsString(XMappingEvent.java:68)
	at sun.awt.X11.XWrapperBase.toString(XWrapperBase.java:12)
	at sun.awt.X11.XMappingEvent.toString(XMappingEvent.java:8)
	at java.lang.String.valueOf(String.java:2827)
	at java.lang.StringBuilder.append(StringBuilder.java:115)
	at sun.awt.X11.XEvent.getFieldsAsString(XEvent.java:115)
	at sun.awt.X11.XWrapperBase.toString(XWrapperBase.java:12)
	at sun.awt.X11.XEvent.toString(XEvent.java:8)
	at sun.awt.X11.XBaseWindow.dispatchEvent(XBaseWindow.java:1075)
	at sun.awt.X11.XBaseWindow.dispatchToWindow(XBaseWindow.java:1070)
	at sun.awt.X11.XToolkit.dispatchEvent(XToolkit.java:471)
	at sun.awt.X11.XToolkit.run(XToolkit.java:584)
	at sun.awt.X11.XToolkit.run(XToolkit.java:519)
	at java.lang.Thread.run(Thread.java:619)