On Fri, 21 Mar 2025 20:56:01 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.
It is better to use dynamically calculated safe limit instead of a hardcoded
value like 250. The dynamic calculation should be based on system resource and
and 250 would be fallback value. like
static int getSafeRunLoopLimit() {
struct rlimit limit;
if (getrlimit(RLIMIT_STACK, &limit) == 0) {
return (int)(limit.rlim_cur / (512 * 1024));
}
return 250; // Fallback to 250 if stack size retrieval fails
}
macOS does not document an exact limit, nested CFRunLoopRun calls can cause
stack growth. 512 KB is a safe approximation.
-------------
PR Comment: https://git.openjdk.org/jfx/pull/1741#issuecomment-2744896944
