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

[Henry Jen]

> On Jun 18, 2019, at 4:09 AM, Maurizio Cimadamore <maurizio.cimadamore at oracle.com> wrote:
> 
> 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’.
> 

Did you change the way you make calls?
I think there is a bug in jni.h, 

typedef JavaVM_ JavaVM;

should be

typedef struct JavaVM_ JavaVM;


Cheers,
Henry

> 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
>>