Thread.dispatchUncaughtException possible NPE?

[Remi Forax]

----- Original Message -----
> From: "Andrey Turbanov" <turbanoff at gmail.com>
> To: "core-libs-dev" <core-libs-dev at openjdk.java.net>
> Sent: Monday, January 17, 2022 10:37:04 AM
> Subject: Thread.dispatchUncaughtException possible NPE?

> Hello.

Hello Andrey,

> I see that Thread.dispatchUncaughtException calls
> getUncaughtExceptionHandler() which reads volatile field twice:
> https://github.com/openjdk/jdk/blob/master/src/java.base/share/classes/java/lang/Thread.java#L1978
> 
> private volatile UncaughtExceptionHandler uncaughtExceptionHandler;
> 
> public UncaughtExceptionHandler getUncaughtExceptionHandler() {
>    return uncaughtExceptionHandler != null ?
>        uncaughtExceptionHandler : group;
> }
> 
> private void dispatchUncaughtException(Throwable e) {
>    getUncaughtExceptionHandler().uncaughtException(this, e);
> }
> 
> 
> I wonder if it's possible to get a NPE here? Another thread could
> change uncaughtExceptionHandler between 2 volatile reads.
> Or JVM somehow forbid this?

yes, it's a bug, the field should be read only once.

> 
> 
> 
> 
> Andrey Turbanov

Rémi