RFR (S): 8238676: jni crashes on accessing it from process exit hook

[Anton Tarasov]

Hi David,

Thanks, please tag it, hope someone else will backport it (or if not I'm
ready to do that job).

With regards,
Anton.

On Tue, Mar 3, 2020 at 1:56 AM David Holmes <david.holmes at oracle.com> wrote:

> Hi Anton,
>
> On 3/03/2020 1:12 am, Anton Tarasov wrote:
> > Hi David,
> >
> > Thank you for fixing this! Is it possible to backport the fix to jdk11?
>
> I can tag it for backporting once it is pushed, but I can't do the
> actual backport for OpenJDK 11u.
>
> David
>
> > Thanks,
> > Anton.
> >
> > On Sat, Feb 29, 2020 at 8:16 AM David Holmes <david.holmes at oracle.com
> > <mailto:david.holmes at oracle.com>> wrote:
> >
> >     Hi Gerard,
> >
> >     Are you okay with this?
> >
> >     Thanks,
> >     David
> >
> >     On 26/02/2020 10:11 am, David Holmes wrote:
> >      > Hi Gerard,
> >      >
> >      > Thanks for taking a look at this.
> >      >
> >      > On 26/02/2020 2:45 am, gerard ziemski wrote:
> >      >> hi David,
> >      >>
> >      >> On 2/18/20 8:04 PM, David Holmes wrote:
> >      >>> Bug: https://bugs.openjdk.java.net/browse/JDK-8238676
> >      >>> webrev: http://cr.openjdk.java.net/~dholmes/8238676/webrev/
> >      >>>
> >      >>> If an application tries to use JNI from an atexit handler, the
> >      >>> attempt can't succeed (the VM has already logically terminated)
> >     but
> >      >>> it should not crash. The JNI Invocation API code was missing
> some
> >      >>> checks in places and wasn't aware of the possibility of trying
> to
> >      >>> make calls from the VMThread.
> >      >>>
> >      >>> Testing:
> >      >>>  - new test added for the JNI Invocation API
> >      >>>  - tiers 1-3
> >      >>>
> >      >>> Thanks,
> >      >>> David
> >      >>
> >      >> In jni_GetEnv() we have:
> >      >>
> >      >> 4120   if (vm_created == 0) {
> >      >> 4121     *penv = NULL;
> >      >> 4122     ret = JNI_EDETACHED;
> >      >> 4123     return ret;
> >      >> 4124   }
> >      >>
> >      >> but in jni_DetachCurrentThread() we have:
> >      >>
> >      >> 4063   if (vm_created == 0) {
> >      >> 4064     HOTSPOT_JNI_DETACHCURRENTTHREAD_RETURN(JNI_ERR);
> >      >> 4065     return JNI_ERR;
> >      >> 4066   }
> >      >>
> >      >> should lines 4064,4065 perhaps be:
> >      >>
> >      >> 4064     HOTSPOT_JNI_DETACHCURRENTTHREAD_RETURN(JNI_EDETACHED);
> >      >> 4065     return JNI_EDETACHED;
> >      >>
> >      >> to be consistent?
> >      >
> >      > Well ... ideally the JNI spec would have considered the question
> of
> >      > "what if the JavaVM is no longer live?" and had an JNI_ENOJVM
> errro
> >      > code. But it doesn't. Nor does it allow for any JNI method to
> return
> >      > JNI_ERR for unexpected errors situations. So we have to adhere to
> >     the
> >      > specifications for each method.
> >      >
> >      > For GetEnv the spec only allows for returning JNI_EDETACHED,
> >      > JNI_EVERSION or JNI_OK. As you can't be attached to a VM that
> >     doesn't
> >      > exist then JNI_EDETACHED is the only possible return code - and
> >     it isn't
> >      > wrong, it just doesn't tell you why you aren't attached.
> >      >
> >      > If you apply the same logic to DetachCurrentThread, and follow
> >     the spec
> >      > then it states
> >      >
> >      > "Trying to detach a thread that is not attached is a no-op."
> >      >
> >      > which suggests we do nothing and report JNI_OK. But I think that
> >     would
> >      > be a disservice to the programmer in the case where the JVM is no
> >     longer
> >      > live. And we're allowed to return "a suitable JNI error code on
> >     failure"
> >      > so that is what I chose to do. And I return JNI_ERR rather than
> >      > JNI_EDETACHED for two reasons:
> >      >
> >      > 1. It is consistent with what we do for attach in the same
> >     circumstance:
> >      >
> >      > jint JNICALL jni_AttachCurrentThread(JavaVM *vm, void **penv, void
> >      > *_args) {
> >      >    HOTSPOT_JNI_ATTACHCURRENTTHREAD_ENTRY(vm, penv, _args);
> >      >    if (vm_created == 0) {
> >      >      HOTSPOT_JNI_ATTACHCURRENTTHREAD_RETURN((uint32_t) JNI_ERR);
> >      >      return JNI_ERR;
> >      >    }
> >      >
> >      > 2. It would be confusing to return JNI_EDETACHED as that means
> >     "thread
> >      > detached from the VM" yet the spec says "Trying to detach a
> >     thread that
> >      > is not attached is a no-op.". So I need to convey that there is a
> >     more
> >      > specific underlying error here.
> >      >
> >      >> Looks good otherwise.
> >      >
> >      > Thanks for the review.
> >      >
> >      > David
> >      > -----
> >      >
> >      >>
> >      >> cheers
> >      >>
> >
>