RFR: 8189633: Missing -Xcheck:jni checking for DeleteWeakGlobalRef

[Kim Barrett]

> On Jan 3, 2018, at 12:31 AM, David Holmes <david.holmes at oracle.com> wrote:
> 
> Hi Kim,
> 
> On 3/01/2018 9:30 AM, Kim Barrett wrote:
>> Please review this change to the checking form of DeleteWeakGlobalRef
>> to actually perform some checking.  The checking that is now being
>> done was cribbed from DeleteGlobalRef.
>> CR:
>> https://bugs.openjdk.java.net/browse/JDK-8189633
>> Webrev:
>> http://cr.openjdk.java.net/~kbarrett/8189633/open.00/
> 
> Doesn't the fact it is a weak-ref mean that resolving it could return NULL, in which case validate_object will trigger a JNI fatal error:
> 
> oop jniCheck::validate_object(JavaThread* thr, jobject obj) {
>    if (!obj)
>        return NULL;
>    ASSERT_OOPS_ALLOWED;
>    oop oopObj = jniCheck::validate_handle(thr, obj);
>    if (!oopObj) {
>      ReportJNIFatalError(thr, fatal_bad_ref_to_jni);
>    }
>    return oopObj;
> }
> 
> ?

You’re right.  I thought I’d used validate_handle, but obviously not.

I think I should leave this issue alone for now, and come back to it after JDK-8194312 is done.
There are some changes to jniCheck there already, and I think some more, like here, can
be simplified or improved by relying on the JDK-8194312 changes to JNIHandles.