fix: pin Task.Factory.StartNew to TaskScheduler.Default (#4071)#4079
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iancooper merged 2 commits intoApr 26, 2026
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…and#4071) Dispatcher.Start, Performer.Run, TimeoutPolicyHandler, and the Mediator Runner/Waker called Task.Factory.StartNew without an explicit scheduler, inheriting TaskScheduler.Current. Under any limited-concurrency scheduler (BrighterAsyncContext, ASP.NET, async test hosts), the spawned tasks queued behind the very thread waiting for them and End() / await never returned. LongRunning is only a hint — only TaskScheduler.Default guarantees a fresh thread. Pass TaskScheduler.Default explicitly at every affected call site and add a regression test using ConcurrentExclusiveSchedulerPair that deadlocks without the fix.
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Closes #4071.
Summary
Dispatcher.Start,Performer.Run,TimeoutPolicyHandler,Mediator.Runner, andMediator.WakercalledTask.Factory.StartNewwithout an explicitTaskScheduler, inheritingTaskScheduler.Current. Under any limited-concurrency scheduler (BrighterAsyncContext, ASP.NET, async test hosts), the control task / message pump queued behind the very thread waiting for them andEnd()/awaitnever returned.TaskCreationOptions.LongRunningis only a hint — onlyTaskScheduler.Defaultguarantees a fresh thread.TaskScheduler.Defaultexplicitly at every affected call site.Performer.Runalso dropped its redundantasync/awaitwrapper.DispatcherOnLimitedConcurrencySchedulerTestsusingConcurrentExclusiveSchedulerPair— verified red without the fix (30 s deadlock) and green with it (~600 ms).Test plan
TaskCreationOptions.LongRunning-only call (deadlock at 30 s) and passes withTaskScheduler.Defaultpin.MessageDispatchtests pass onnet9.0.net9.0(2 pre-existing skips on obsolete Timeout API).Paramore.Brighter.ServiceActivatorandParamore.Brighter.Mediatorbuild clean.