I've had a webapplication with JRebel running and set a method breakpoint in an exception. Then this exception popup up:
Read access is allowed from event dispatch thread or inside read-action only (see com.intellij.openapi.application.Application.runReadAction())
Details: Current thread: Thread[ApplicationImpl pooled thread,5,Idea Thread Group] 23857951
Our dispatch thread:Thread[AWT-EventQueue-1 9.0.1#IU-93.67, eap:true,6,Idea Thread Group] 4524013
SystemEventQueueThread: Thread[AWT-EventQueue-1 9.0.1#IU-93.67, eap:true,6,Idea Thread Group] 4524013
java.lang.Throwable
at com.intellij.openapi.diagnostic.Logger.error(Logger.java:52)
at com.intellij.openapi.application.impl.ApplicationImpl.assertReadAccessAllowed(ApplicationImpl.java:787)
at com.intellij.psi.impl.compiled.ClsFileImpl.getStubTree(ClsFileImpl.java:371)
at com.intellij.psi.impl.compiled.ClsFileImpl.getStub(ClsFileImpl.java:364)
at com.intellij.psi.impl.compiled.ClsFileImpl.getClasses(ClsFileImpl.java:128)
at com.intellij.psi.impl.compiled.ClsFileImpl.getChildren(ClsFileImpl.java:123)
at com.intellij.psi.impl.compiled.ClsElementImpl.a(ClsElementImpl.java:186)
at com.intellij.psi.impl.compiled.ClsElementImpl.findElementAt(ClsElementImpl.java:153)
at com.zeroturnaround.javarebel.idea.plugin.debugger.JavaRebelPositionManager.getClassAt(JavaRebelPositionManager.java:189)
at com.zeroturnaround.javarebel.idea.plugin.debugger.JavaRebelPositionManager.createPrepareRequest(JavaRebelPositionManager.java:75)
at com.intellij.debugger.engine.CompoundPositionManager.createPrepareRequest(CompoundPositionManager.java:86)
at com.intellij.debugger.engine.requests.RequestManagerImpl.callbackOnPrepareClasses(RequestManagerImpl.java:307)
at com.intellij.debugger.ui.breakpoints.Breakpoint.createOrWaitPrepare(Breakpoint.java:129)
at com.intellij.debugger.ui.breakpoints.BreakpointWithHighlighter.createRequest(BreakpointWithHighlighter.java:304)
at com.intellij.debugger.engine.requests.RequestManagerImpl$4.action(RequestManagerImpl.java:433)
at com.intellij.debugger.engine.requests.RequestManagerImpl$3.action(RequestManagerImpl.java:423)
at com.intellij.debugger.engine.events.DebuggerCommandImpl.run(DebuggerCommandImpl.java:48)
at com.intellij.debugger.engine.DebuggerManagerThreadImpl.processEvent(DebuggerManagerThreadImpl.java:148)
at com.intellij.debugger.engine.DebuggerManagerThreadImpl.processEvent(DebuggerManagerThreadImpl.java:36)
at com.intellij.debugger.impl.InvokeThread.run(InvokeThread.java:139)
at com.intellij.debugger.impl.InvokeThread$WorkerThreadRequest.run(InvokeThread.java:56)
at com.intellij.openapi.application.impl.ApplicationImpl$5.run(ApplicationImpl.java:328)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:619)
at com.intellij.openapi.application.impl.ApplicationImpl$1$1.run(ApplicationImpl.java:124)