While it might be possible to make the shutdown experience a little more
graceful, your expectation of being able to use the GUI after the start
of the shutdown sequence is unlikely to be met. Quoting from the
shutdown docs [1] :
"Shutdown hooks run at a delicate time in the life cycle of a virtual
machine ... Attempts to use other thread-based services such as the AWT
event-dispatch thread, for example, may lead to deadlocks.
Shutdown hooks should also finish their work quickly. When a program
invokes exit, the expectation is that the virtual machine will promptly
shut down and exit. When the virtual machine is terminated due to user
logoff or system shutdown the underlying operating system may only allow
a limited amount of time in which to shut down and exit. *It is
therefore inadvisable to attempt any user interaction or to perform a
long-running computation in a shutdown hook.*"
Note, particularly, that last sentence. Asking JavaFX to ignore the fact
that there is a shutdown in progress doesn't change that. Having said
that, I can take another look at this (not right away, though) and see
what else we can do.
-- Kevin
[1]
https://docs.oracle.com/en/java/javase/22/docs/api/java.base/java/lang/Runtime.html#addShutdownHook(java.lang.Thread)
On 7/26/2024 10:11 AM, PavelTurk wrote:
Hello, Kevin
Yes, I filed that enhancement request.
When user presses CTRL+C then SIGINT signal is sent to the process.
SIGINT is a signal used to request a graceful termination of a
process, typically initiated by the user(more details are here
https://urldefense.com/v3/__https://stackoverflow.com/a/4047975__;!!ACWV5N9M2RV99hQ!Kubf8U462HbtwSv0HaNgAZNyYpFS94_WfV0T8TAjTcNx56xb2lUr9jPR5ezZHSUjZ1C-tStV9j5KxWUduzx7XjC0BR1D$
).
Now, we are talking about GUI application (if we didn't develop a GUI
application, we wouldn't need JavaFX, would we?). So, our GUI
application gets SIGINT or SIGTERM (I didn't test with SIGTERM, but I
think result is the same) and after that immediately stops working
because of the damned shutdown hook. For example, if our application
is a simple text editor, our application can't let user save file.
Why? Because GUI platform doesn't work anymore.
That's why I opened that issue. I saw you suggested working with
exceptions. But that issue is not about exceptions, but about letting
application developers control when to shutdown platform.
Best regards, Pavel
On 7/26/24 16:54, Kevin Rushforth wrote:
I am not sure we will want to disabling the shutdown hook, since that
is likely to cause problems (they were added to fix bugs that
resulted from applications calling System.exit()).
In the bug report for JDK-8320923, you mentioned that Swing doesn't
have this problem, but that's because Swing closes all of its windows
before effecting the shutdown (that's something JavaFX could do as
well).
Related to this, I see that someone (perhaps it was you?) just filed
an enhancement request to consider optionally disabling the shutdown
hook:
https://bugs.openjdk.org/browse/JDK-8337247
I haven't looked at it closely, but my sense is that disabling the
shutdown hooks in a way that tries to keep the JavaFX runtime active
is unlikely to be something we want to do. I added the following
comment to the above JBS issue with some initial thoughts:
--------------------------------------------------
“I can take a look, but I do not think we will implement this
Enhancement request -- at least not as described.
Instead, we might consider whether this can be done using existing
mechanisms, such as overriding Application::exit. If it turns out
there isn't a suitable existing mechanism, we might consider other
solutions. A couple possibilities:
1. Provide a Platform setting that will cause Platform.runLater to
throw an exception if called after shutdown (this might be require
adding a few try/catch blocks in our own cleanup code)
2. Rather than a setting as described above, create a new overload of
Platform.runLater that throws an exception if the Platform is not
able to queue the request.
There might be other solutions.”
-------------------------------------------------------
-- Kevin
On 7/25/2024 8:43 AM, PavelTurk wrote:
Hello all.
JavaFX adds its own shutdown hook. That gives many problems when it
is necessary to work with application,
when system is shutting down, for example, if user presses CTRL+C.
The first problem I described here -
https://bugs.openjdk.org/browse/
Another problem is that after pressing CTRL+C JavaFX seems not to
respond anymore. For example I've
observed that if after that we try to do Platform.runLater(() ->
myCode is here), then myCode will never execute.
So, it is necessary to check in system, how it is shutting down, if
it is. And this problem creates other problems.
Before opening a feature request, I decided to ask JavaFX
developers, if it possible to disable JavaFX shutdown hook.
I mean, if there is no system property (something like
javafx.shutdownhook.disabled), it will be added, but if I want
to call Platform.exit() manually I want to be able to disable JavaFX
shutdown hook.
Best regards, Pavel
