[foreign] RFR 8226250: Calling callback from different native threads causes a VM crash

[Maurizio Cimadamore]

Fixed aarch64 problems and pushed.

Henry, I tried to address your comment, but CPP complains if I just 
replace JavaVM_ with JavaVM. I also noted that the same pattern is 
spread everywhere in hotspot, so I figured it was 'ok'.

Of course if somebody knows a better way to do this, we can update the code.

Cheers
Maurizio

On 17/06/2019 18:14, Maurizio Cimadamore wrote:
> Hi,
> Under JNI, it is user responsibility to attach native threads to the 
> VM using attachCurrentThread/detachCurrentThread.
>
> Panama doesn't do this and, as a result, if native code creates a new 
> thread and uses it to call a Java callback, an hard crash occurs.
>
> This patch adds a call to AttachCurrentThreadAsDaemon before calling 
> the Java callback, only if the native thread has no associated Java 
> thread.
>
> The AttachCurrentThreadAsDaemon allows the VM to be shutdown w/o 
> waiting for native threads to complete, which is, I think the 
> semantics we want.
>
> We don't call the dual detach method for two reasons:
>
> * re-attaching the same thread over and over can be expensive
>
> * calling detach after the callback means that we'd lose some register 
> values, so we would additional save/restore
>
> Overall, it seems like the 'leak' of JavaThread is not worth the extra 
> complexity?
>
> Webrev:
>
> http://cr.openjdk.java.net/~mcimadamore/panama/8226250_v2/
>
> Maurizio
>