Our code and some libraries do enter some nested event loops at a few
places when it makes sense, but we didn't do anything to explicitly
provoke this, this occurred naturally in our application. So it would be
nice if JavaFX could somehow guard against this, especially since
crashing the JVM is probably the worst thing that can happen.
I looked at the documentation, but it seems like the public API at
Platform::enterNestedEventLoop does not mention this.
From my understanding, the method Platform::canStartNestedEventLoop is
potentially the right method to indicate to the caller that the limit is
close by returning false.
And even if something like an exception is thrown when a nested event
loop is started while it is close to the limit, that would still be much
better than a direct crash.
Best
Christopher Schnick
On 10/03/2025 18:51, Andy Goryachev wrote:
This looks to me like it might be hitting the (native) thread stack
size limit.
c.s.glass.ui.Application::enterNestedEventLoop() even warns about it:
* An application may enter several nested loops recursively.
There's no
* limit of recursion other than that imposed by the native stack
size.
-andy
*From: *openjfx-dev <openjfx-dev-r...@openjdk.org> on behalf of Martin
Fox <martinfox...@gmail.com>
*Date: *Monday, March 10, 2025 at 10:10
*To: *Christopher Schnick <crschn...@xpipe.io>
*Cc: *OpenJFX <openjfx-dev@openjdk.org>
*Subject: *Re: JVM crashes on macOS when entering too many nested
event loops
Hi Christopher,
I was able to reproduce this crash. I wrote a small routine that
recursively calls itself in a runLater block and then enters a nested
event loop. The program crashes when creating loop 254. I’m not sure
where that limit comes from so it’s possible that consuming some other
system resource could lower it. I couldn’t see any good way to
determine how many loops are active by looking at the crash report
since it doesn’t show the entire call stack.
I did a quick trial on Linux and was able to create a lot more loops
(over 600) but then started seeing erratic behavior and errors coming
from the Java VM. The behavior was variable unlike on the Mac which
always crashes when creating loop 254.
Martin
> On Mar 7, 2025, at 6:24 AM, Christopher Schnick <crschn...@xpipe.io>
wrote:
>
> Hello,
>
> I have attached a JVM fatal error log that seemingly was caused by
our JavaFX application entering too many nested event loops, which
macOS apparently doesn't like.
>
> As far as I know, there is no upper limit defined on how often an
event loop can be nested, so I think this is a bug that can occur in
rare situations.
>
> Best
> Christopher Schnick<hs_err_pid.txt>
