Re: RFR(XS): 8234882: JVM TI StopThread should only allow ThreadDeath

Fri, 29 May 2020 12:51:50 -0700

Hi David and reviewers,

The updated webrev version is:
  http://cr.openjdk.java.net/~sspitsyn/webrevs/2020/jvmti-stop-thread.2/src/

This update adds testing that StopThread can return JVMTI_ERROR_INVALID_OBJECT error code.

The JVM TI StopThread spec is:
  http://cr.openjdk.java.net/~sspitsyn/webrevs/2020/jvmti-stop-thread.2/docs/specs/jvmti.html#StopThread


There is a couple of comments below.


On 5/29/20 06:18, David Holmes wrote:
On 29/05/2020 6:24 pm, serguei.spit...@oracle.com wrote:
On 5/29/20 00:56, serguei.spit...@oracle.com wrote:
On 5/29/20 00:42, serguei.spit...@oracle.com wrote:
Hi David,

Thank you for reviewing this!

On 5/28/20 23:57, David Holmes wrote:
Hi Serguei,

On 28/05/2020 3:12 pm, serguei.spit...@oracle.com wrote:
Hi David,

I've updated the CSR and webrev in place.

The changes are:
  - addressed David's suggestion to rephrase StopThread description change
  - replaced JVMTI_ERROR_INVALID_OBJECT with JVMTI_ERROR_ILLEGAL_ARGUMENT
  - updated the implementation in jvmtiEnv.cpp to return JVMTI_ERROR_ILLEGAL_ARGUMENT
  - updated one of the nsk.jvmti StopThread tests to check error case with the JVMTI_ERROR_ILLEGAL_ARGUMENT


I'm reposting the links for convenience.

Enhancement:
   https://bugs.openjdk.java.net/browse/JDK-8234882

CSR draft:
   https://bugs.openjdk.java.net/browse/JDK-8245853

Spec updates are good - thanks.

Thank you for the CSR review.

Webrev:
http://cr.openjdk.java.net/~sspitsyn/webrevs/2020/jvmti-stop-thread.1/src/

src/hotspot/share/prims/jvmtiEnv.cpp

The ThreadDeath check is fine but I'm a bit confused about the additional null check that leads to JVMTI_ERROR_INVALID_OBJECT. I can't see how resolve_external_guard can return NULL when not passed in NULL. Nor why that would result in JVMTI_ERROR_INVALID_OBJECT rather than JVMTI_ERROR_NULL_POINTER. And I note JVMTI_ERROR_NULL_POINTER is not even a listed error for StopThread! This part of the change seems unrelated to this issue.

I was also surprised with the JVMTI_ERROR_NULL_POINTER and JVMTI_ERROR_INVALID_OBJECT error codes.
The JVM TI spec automatic generation adds these two error codes for a jobject parameter.

Also, they both are from the Universal Errors section:
http://cr.openjdk.java.net/~sspitsyn/webrevs/2020/jvmti-stop-thread.1/docs/specs/jvmti.html#universal-error

You can find a link to this section at the start of the Error section:
http://cr.openjdk.java.net/~sspitsyn/webrevs/2020/jvmti-stop-thread.1/docs/specs/jvmti.html#StopThread

My understanding (not sure, it is right) is that NULL has to be reported with JVMTI_ERROR_NULL_POINTER and a bad
jobject (for instance, a WeakReference with a GC-ed target) has to be reported with JVMTI_ERROR_INVALID_OBJECT.
At least, I was not able to construct a test case to get this error code returned.
So, I'm puzzled with this. I'll try to find some examples with JVMTI_ERROR_NULL_POINTER errors.

Found the explanation.
The JDI file:
  src/jdk.jdi/share/classes/com/sun/tools/jdi/JDWPException.java

has a fragment that translate the INVALID_OBJECT error to the ObjectCollectedException:
    RuntimeException toJDIException() {
        switch (errorCode) {
            case JDWP.Error.INVALID_OBJECT:
                return new ObjectCollectedException();

So, the INVALID_OBJECT is for a jobject handle that is referencing a collected object.
It means that previous implementation incorrectly returned JVMTI_ERROR_NULL_POINTER error code.

I should create and delete local or global ref to construct a test case for this.

Interesting that the JDWPException::toJDIException() does not convert the ILLEGAL_ARGUMENT error code to an IllegalArgumentException.
I've just added this conversion.

Given the definition of JDWP INVALID_OBJECT then obviously JDI converts it to ObjectCollectedException.

So reading further in JNI spec:

"Weak global references are a special kind of global reference. Unlike normal global references, a weak global reference allows the underlying Java object to be garbage collected. Weak global references may be used in any situation where global or local references are used."

So it seems that any function that takes a jobject cxould in fact accept a jweak, in which case JVMTI_ERROR_INVALID_OBJECT is a possibility in all cases. So IIUC JNIHandles::resolve_external_guard can return NULL if a weak reference has been collected. So the new code you propose seems correct.

You are right about weak global references.
I was able to construct a test case for JVMTI_ERROR_INVALID_OBJECT.
The JNI NewGlobalRef and DeleteGlobalRef are used for it.
You can find it in the updated webrev version.

However, this still is unrelated to the current issue and I do not see other JVM TI doing checks for this case. So this seems to be a much broader issue.
There are many such checks in JVM TI.
For instance, there are checks like the following in jvmtiEnv.cpp:
  NULL_CHECK(o, JVMTI_ERROR_INVALID_OBJECT)

Thanks,
Serguei


David
-----

Thanks,
Serguei



Thanks,
Serguei

test/hotspot/jtreg/vmTestbase/nsk/jvmti/StopThread/stopthrd006/TestDescription.java

The copyright year should be change to "2018, 2020,".
Thank you for the catch.
I planned to update the copyright comments.

I'm a little surprised the test doesn't actually check that a valid call doesn't produce an error. But that's an existing quirk of the test and not something you need to address here (if indeed it needs addressing - perhaps there is another test for that).

There are plenty of other nsk.jvmti tests which check valid calls.

Thanks,
Serguei

Thanks,
David
-----


Updated JVM TI StopThread spec:
http://cr.openjdk.java.net/~sspitsyn/webrevs/2020/jvmti-stop-thread.1/docs/specs/jvmti.html#StopThread


The old webrev and spec are here:
http://cr.openjdk.java.net/~sspitsyn/webrevs/2020/jvmti-stop-thread.0/


Thanks,
Serguei

On 5/27/20 18:03, serguei.spit...@oracle.com wrote:
Hi David,


On 5/27/20 02:00, David Holmes wrote:
On 27/05/2020 6:36 pm, serguei.spit...@oracle.com wrote:
Hi David,


On 5/27/20 00:47, David Holmes wrote:
Hi Serguei,

On 27/05/2020 1:01 pm, serguei.spit...@oracle.com wrote:
Please, review a fix for:
https://bugs.openjdk.java.net/browse/JDK-8234882

CSR draft (one CSR reviewer is needed before finalizing it):
https://bugs.openjdk.java.net/browse/JDK-8245853

I have some thoughts on the wording which I will add to the CSR.

Thank you a lot for looking at this!

Also on reflection I think JVMTI_ERROR_ILLEGAL_ARGUMENT would the best error to use, and it has an equivalent in JDWP and at the Java level for JDI.

This is an interesting variant, thanks!
We need to balance on several criteria:
  1) Compatibility: keep returning error as close as possible to the current spec

If you are adding a new error condition I don't understand what you mean by "close to the current spec" ??

If the JVMTI_ERROR_INVALID_OBJECT is returned than the JDWP agent does not need any new error handling.
The same can be true in the JDI if the JDWP returns the same error as it returned before.
In this case we do not add new error code but extend the existing to cover new error condition.

But, in fact (especially, after rethinking), I do not like the JVMTI_ERROR_INVALID_OBJECT
error code as it normally means something different.
So, let's avoid using it and skip this criteria.
Then we need new error code to cover new error condition.

  2) Best error naming match between JVM TI and JDI/JDWP
  3) Best practice in errors naming

If the argument is not a ThreadDeath instance then it is an illegal argument - perfect fit semantically all the specs involved have an "illegal argument" error form.

I agree with this.
It is why I like this suggestion. :)
The JDWP equivalent is: ILLEGAL_ARGUMENT.
The JDI equivalent is:  IllegalArgumentException

I'll prepare and send the update.

Thanks!
Serguei


Cheers,
David

I think the #1 is most important but will look at it once more.

Thanks,
Serguei

Thanks,
David

Webrev:
http://cr.openjdk.java.net/~sspitsyn/webrevs/2020/jvmti-stop-thread.1/src/

Updated JVM TI StopThread spec:
http://cr.openjdk.java.net/~sspitsyn/webrevs/2020/jvmti-stop-thread.1/docs/specs/jvmti.html#StopThread

Summary:

   The JVM TI StopThread method mirrored the functionality of the
   java.lang.Thread::stop(Throwable t) method, in that it allows any exception
   type to be installed as an asynchronous exception in the target thread.
   However, the java.lang.Thread::stop(Throwable t) method was inherently unsafe
   and in Java 8 (under JDK-7059085) it was "retired" so that it always threw
   UnsupportedOperationException.
   The updated JVM TI StopThread spec disallows an arbitrary Throwable from being passed,
   and instead restricts the argument to being an instance of ThreadDeath, thus
   mirroring the (deprecated but still functional) java.lang.Thread::stop() method.
   The error JVMTI_ERROR_INVALID_OBJECT is returned if the exception argument
   is not an instance of ThreadDeath.

   Also, I will file similar RFE and CSR on the JDI and JDWP spec.


Testing:
   Built docs and checked the doc has been generated as expected.
   Will run the nsk.jvmti tests locally.
   Will submit hs-tiers1-3 to make sure there are no regressions in the JVM TI and JDI tests.

Thanks,
Serguei







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