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

[Samuel Audet]

Hi, Maurizio,

What about just leaving the choice up to the user? It works fine in JavaCPP:
https://github.com/bytedeco/javacpp/issues/143#issuecomment-262138799

Samuel

On 6/18/19 2:14 AM, 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
>