I'm not sure if I'm doing the wrong thing, or if I've bumped into a problem with step <Over>. I'm trying to add some debugging support into multi-threaded code to help properly sequence debugging different priority processes. I've extracted a little demo... TestCase subclass: #Example instanceVariableNames: 'doCycle debug highPriorityProcess' classVariableNames: '' package: 'KernelX-DelayScheduler' Example >> highPriorityCycle debug ifTrue: [ self halt ]. Transcript show: 'H'. Example >> highPriorityRunLoop doCycle := Semaphore new. ^[ [ doCycle wait. self highPriorityCycle ] repeat. ] forkAt: 45 named: 'Example high side' Process >> isWaiting ^myList isKindOf: Semaphore Example >> wakeHighPriorityLoop doCycle signal. debug ifTrue: [ "wait until high priority process is sleeping" [ highPriorityProcess isWaiting & highPriorityProcess isTerminated not] whileFalse: [ Transcript show: '.'. 100 milliSeconds wait ]. self halt ]. Example >> testUserPriority debug := true. highPriorityProcess := self highPriorityRunLoop. Transcript cr. debug ifTrue: [self halt]. 3 timesRepeat: [ Transcript crShow: 'U'. self wakeHighPriorityLoop.]. highPriorityProcess terminate. Running #testUserPriority, on Transcript you'll see.... UH UH UH _______________ Changing "debug := true" and run #testUserPriority and the UI will lockup, until "TestTookTooMuchTime" appears. But it works with the following change... ClyRunTestsFromMethodsCommand >> runTest: testSelector of: testClass [ | testResult | testResult := testClass debug: testSelector. self notifyUserAboutResults: testResult with: 'Method: ' , testClass asString , '>>#' , testSelector asString ] forkNamed: 'TESTING ' , testClass asString , '>>#' , testSelector asString Now running #testUserPriority and pressing <Proceed> at each pre-debug window gives the following result... U................H U..............H U............H It also works properly to run #testUserPriority and debug <Into> #wakeHighPriorityLoop initially ignoring the #highPriorityCycle pre-debug that pops up to step around the #whileFalse: loop a few times. Then <Proceed>ing the #highPriorityCycle pre-debug and stepping until out of #wakeHighPriorityLoop. Works fine. However running #testUserPriority, debugging into #wakeHighPriorityLoop but stepping <Over> #wakeHighPriorityLoop locks up the UI, and I can't tell why. Can anyone advise? cheers -ben P.S. What I'm trying to do it make it easier for others to trace the operation of the delay scheduler to understand its unit tests.