The only thing that needs to be part of the API is the run loop mode *name*. If for some reason in the future the JDK stops using a native run loop when the AppKit main thread calls Java, there is no harm if a native (JNI) library calls performOnMainThread and passes that name as one of the run loop modes. The obsolete run loop mode name will have no effect if no native run loop uses that name.
A problem arises only if the run loop mode name is *changed* and the run loop mode is still important, which is the case now. I don’t think it matters how rare the problem is. There was no reason to change the name of the run loop mode, so even *one* new deadlock is a regression. I have two examples, but only one is repeatable. That doesn’t mean the other one isn’t important. To be clear about my repeatable example, my Java code running on the AWT thread starts a secondary Java run loop because it wants to block on the result of the native file dialog. AppKit is calling Java because the native file dialog contains an accessory view that is implemented using a Swing component. This works fine before your change. Although this example deadlocks reliably, I don’t see how it would help you. I think the problem is obvious. Using JavaNativeFoundation to perform code on the main thread (which is how third party JNI libraries have been told to do it), the old run loop mode name is used, so the code is not performed while the AppKit main thread is blocked in a JDK-implemented native run loop. If the JNI library was called on the AWT thread and the AppKit main thread is waiting for its code to be performed on the AWT thread, deadlock results. The second example uses a native file dialog (no accessory) and deadlocks when a key shortcut is used causing AppKit to inquire about the application menus. It is more timing sensitive and has happened only once. >> Changing the name seems to have at least been useful to find cases such as >> this which I suspect are very, very rare. I trust you are being sarcastic. I have yet to see a CSR that says an incompatible change is being made solely to find out what breaks. Alan > On Jul 8, 2021, at 2:39 PM, Philip Race <philip.r...@oracle.com> wrote: > > > Changing the name seems to have at least been useful to find cases such as > this which I suspect are very, very rare. > > > My Java code sets up a secondary run loop. > > But JDK only enters that mode if *it* creates a secondary run loop. > > > The AppKit implementation of the file dialog calls Java to get > > accessibility information. > > Why would Appkit call Java to ask about A11y info for a platform native > dialog ? > > I suppose the situation isn't as clear to me as it should be. > > I might be asking a lot but is there a test case you can provide ? > > As to making something like this part of a "public API" it seems to me that > Java setting up this > mode in a 2ndary run loop in some situations is really an implementation > choice and I wouldn't > know where to expose it even if it were something appropriate to do. > I'd sooner find a way to dispense with it entirely. > In fact there is some provision when doing FX interop to not use this mode at > all. > > -phil. > > > On 6/28/21 5:51 AM, Alan Snyder wrote: >> Hmm… it appears that in removing JavaNativeFoundation from the JDK the name >> of the run loop was changed from AWTRunLoopMode to javaRunLoopMode. >> >> If that is correct, it is an incompatible change that breaks third party use >> of JavaNativeFoundation for running code on the main thread. >> >> It also sounds like a gratuitous change. >> >> >> >>> On Jun 27, 2021, at 10:24 AM, Alan Snyder <javali...@cbfiddle.com> wrote: >>> >>> I have a program that reliably deadlocks when run on JDK 17, but not on JDK >>> 16 (although that may be due to timing differences, so it may not imply a >>> new bug). >>> >>> It’s a fairly complicated situation. >>> >>> On the AWT thread, my program calls native code that displays a native file >>> dialog. My Java code sets up a secondary run loop. The native code blocks >>> on JNFRunLoop performOnMainThread to create the native file dialog. >>> >>> The AppKit implementation of the file dialog calls Java to get >>> accessibility information. This sets up a run loop on the main thread and >>> upcalls to Java. I presume this posts an AWT event. >>> >>> Before the AWT secondary run loop can process the request for accessibility >>> information, it runs an invocation event (previously posted by a timer) >>> that calls native code. This native code blocks attempting to perform code >>> on the main thread using JNFRunLoop. Apparently, this request is never >>> processed and the AWT thread remains blocked forever. >>> >>> If I change this latter native code to perform the main thread operation >>> without blocking, there is no deadlock and all is fine. >>> >>> But I have encountered other deadlocks (not reliably repeatable) where this >>> option is not available. Therefore, I would like to understand why this >>> deadlock is happening. >>> >>> With run loops on both threads, what would cause the deadlock? >>> >>> [Question: does JDK 17 and JNFRunLoop use the same NSString to identify the >>> java run loop mode? If not, might that matter?] >>> >>> I would appreciate any suggestions of what might be going wrong or how to >>> track it down. >>> >>> Alan >>> >
