On Mon, 24 Mar 2025 15:30:33 GMT, Martin Fox <[email protected]> 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.
>
> Martin Fox has updated the pull request incrementally with one additional
> commit since the last revision:
>
> Added explanation for limit on nested run loop calls
modules/javafx.graphics/src/main/java/com/sun/javafx/tk/quantum/QuantumToolkit.java
line 637:
> 635: if (!canStartNestedEventLoop()) {
> 636: if (!Application.GetApplication().canStartNestedEventLoop())
> {
> 637: throw new RuntimeException("Exceeded limit on nested
> event loops");
should we tell what the limit is (using the static constant mentioned earlier)?
e.g.
"Too many nested event loops (250)"? or something like that.
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PR Review Comment: https://git.openjdk.org/jfx/pull/1741#discussion_r2010377313
