On Fri, 21 Mar 2025 20:56:01 GMT, Martin Fox <m...@openjdk.org> wrote:
> There is an undocumented limit on nesting calls to CFRunLoopRun (or the
> equivalent wrapper NSRunLoop methods). When the limit is hit the OS
> terminates the Java app. The situation arises when a JavaFX app creates too
> many nested event loops from within Platform.runLater runnables.
>
> This PR doesn't change the limit (which is 250+ nested loops) but it does
> throw an exception just before the limit is reached so a JavaFX developer
> will get a useful Java stack trace instead of an OS crash log.
>
> On the Mac the nested event loop has two stages: first we ask the run loop to
> run, then we pull an event out and process it. A Platform.runLater runnable
> is executed in the first stage so if the runnable starts a new nested event
> loop the system will re-enter CFRunLoopRun. The same isn't true if an input
> event handler starts a new nested event loop; at that point we're in stage
> two and are past the call to CFRunLoopRun.
If the hard-coded 250 is a robust limit, then the fix looks reasonable to me.
I'll test it and finish the review next week.
modules/javafx.graphics/src/main/native-glass/mac/GlassApplication.m line 759:
> 757: + (BOOL)canStartNestedEventLoop
> 758: {
> 759: return nestedRunLoopRunCount <= 250;
How sure are you that 250 is a safe limit? Are there situations where we might
not be able to do this many?
I recommend added a comment as to where the magic number "250" comes from. And
maybe put it in a static const variable?
-------------
PR Review: https://git.openjdk.org/jfx/pull/1741#pullrequestreview-2707278351
PR Review Comment: https://git.openjdk.org/jfx/pull/1741#discussion_r2008341553
