RFR (S) 8210842: Handle JNIGlobalRefLocker.cpp
JC Beyler
jcbeyler at google.com
Wed Sep 19 22:56:47 UTC 2018
Hi Alex,
I've updated the webrev to:
Webrev: http://cr.openjdk.java.net/~jcbeyler/8210842/webrev.02/
Bug: https://bugs.openjdk.java.net/browse/JDK-8210842
That webrev has the code that is shown here in snippets.
Thanks for the reviews, I've relatively followed your reviews except for
one detail due to me wanting to handle the NSK_JNI_VERIFY macros via this
system as well later down the road. For an example:
We currently have in the code:
if ( ! NSK_JNI_VERIFY(pEnv, (mhClass = NSK_CPP_STUB2(GetObjectClass, pEnv,
mhToCall)) != NULL) )
1) The NSK_CPP_STUB2 is trivially removed with a refactor (JDK-8210728)
<https://bugs.openjdk.java.net/browse/JDK-8210728> to:
if ( ! NSK_JNI_VERIFY(pEnv, (mhClass = pEnv->GetObjectClass(pEnv,
mhToCall)) != NULL) )
2) Then the NSK_JNI_VERIFY, I'd like to remove it to and it becomes via
this wrapping of JNIEnv:
if ( ! (mhClass = pEnv->GetObjectClass(pEnv, mhToCall)) )
3) Then, via removing the assignment, we'd arrive to a:
mhClass = pEnv->GetObjectClass(pEnv, mhToCall));
if (!mhClass)
Without any loss of checking for failures, etc.
So that is my motivation for most of this work with a concrete example
(hopefully it helps drive this conversation).
I inlined my answers here, let me know what you think.
On Wed, Sep 19, 2018 at 2:30 PM Alex Menkov <alexey.menkov at oracle.com>
wrote:
> Hi Jc,
>
> Updated tests looks good.
> Some notes about implementation.
>
> - FatalOnException implements both verification and error handling
> It would be better to separate them (and this makes easy to implement
> error handling different from JNIEnv::FatalError).
> The simplest way is to define error handler as
> class SafeJNIEnv {
> public:
> typedef void (*ErrorHandler)(JNIEnv *env, const char* errorMsg);
> // error handler which terminates jvm by using FatalError()
> static void FatalError(JNIEnv *env, const char *errrorMsg);
>
> SafeJNIEnv(JNIEnv* jni_env, ErrorHandler errorHandler = FatalError);
> (SafeJNIEnv methods should create FatalOnException objects passing
> errorHandler)
>
Agreed, I tried to keep the code simple. The concepts you talk about here
are generally what I reserve for when I need it (ie extensions and handling
new cases). But a lot are going to be needed soon so I think it is a good
time to iron the code out now on this "simple" webrev.
So done for this.
>
>
> - FatalOnException is used in SafeJNIEnv methods as
> FatalOnException marker(this, "msg");
> ret = <JNI call>
> (optional)marker.check_for_null(ret);
> return ret;
> But actually I'd call it something like JNICallResultVerifier and create
> the object after JNI call. like
> ret = <JNI call>
> JNICallResultVerifier(this, "msg")
> (optional).notNull(ret);
> return ret;
> or even (if you like such syntax sugar) you can define
> template<typename T>
> T resultNotNull(T result) {
> notNull(result);
> return result;
> }
> and do
> ret = <JNI call>
> return JNICallResultVerifier(this, "msg").resultNotNull(ret);
>
So I renamed FatalOnException to now being JNIVerifier.
Though I like it, I don't think we can do it, except if we do it slightly
differently:
I'm trying to solve two problems with one stone:
- How to check for returns of JNI calls in the way that is done here
- How to remove NSK_JNI_VERIFY* (from nsk/share/jni/jni_tools)
However, the NSK_JNI_VERIFY need to start a tracing system before the call
to JNI, so it won't work this way. (Side question would be do we still care
about the tracing in NSK_JNI_VERIFY, if we don't then your solution works
well in most situations).
My vision or intuition is that we would throw a template at some point on
SafeJNIEnv to handle both cases and have JNIVerifier become a
specialization in certain cases and something different for the
NSK_JNI_VERIFY case (or have a different constructor to enable tracing).
But for now, I offer the implementation that does:
jclass SafeJNIEnv::GetObjectClass(jobject obj) {
JNIVerifier<jclass> marker(this, "GetObjectClass");
return marker.ResultNotNull(_jni_env->GetObjectClass(obj));
}
and:
void SafeJNIEnv::SetObjectField(jobject obj, jfieldID field, jobject value)
{
JNIVerifier<> marker(this, "SetObjectField");
_jni_env->SetObjectField(obj, field, value);
}
>
>
> - you added #include <memory> in the test (and you have to add it to
> every test).
> It would be simpler to add the include to SafeJNIEnv.hpp and define
> typedef std::unique_ptr<SafeJNIEnv> SafeJNIEnvPtr;
> Then each in the test methods:
> SafeJNIEnvPtr env(new SafeJNIEnv(jni_env));
> or you can add
> static SafeJNIEnv::SafeJNIEnvPtr wrap(JNIEnv* jni_env, ErrorHandler
> errorHandler = fatalError)
> and get
> SafeJNIEnvPtr env = SafeJNIEnv::wrap(jni_env);
>
Done, I like that, even less code change to tests then.
>
>
> - it would be better to wrap internal classes (FatalOnException) into
> unnamed namespace - this helps to avoid conflicts with other classes)
>
> - FatalOnException::check_for_null(void* ptr)
> should be
> FatalOnException::check_for_null(const void* ptr)
> And calling the method you don't need reinterpret_cast
>
Also done, it got renamed to ResultNotNull, is using a template now, but
agreed, that worked.
Thanks again for the review,
Jc
> --alex
>
>
> On 09/18/2018 11:07, JC Beyler wrote:
> > Hi David,
> >
> > Thanks for the quick review and thoughts. I have now a new version here
> > that addresses your comments:
> >
> > Webrev: http://cr.openjdk.java.net/~jcbeyler/8210842/webrev.01/
> > <http://cr.openjdk.java.net/%7Ejcbeyler/8210842/webrev.01/>
> > Bug:https://bugs.openjdk.java.net/browse/JDK-8210842
> >
> > I've also inlined my answers/comments.
> >
> >
> >
> > > I've slowly started working on JDK-8191519
> > > <https://bugs.openjdk.java.net/browse/JDK-8191519>. However
> before
> > > starting to really refactor all the tests, I thought I'd get a few
> > > opinions. I am working on internalizing the error handling of JNI
> > calls
> > > via a SafeJNIEnv class that redefines all the JNI calls to add an
> > error
> > > checker.
> > >
> > > The advantage is that the test code will look and feel like
> > normal JNI
> > > code and calls but will have the checks we want to have for our
> > tests.
> >
> > Not sure I get that. Normal JNI code has to check for
> errors/exceptions
> > after every call. The tests need those checks too. Today they are
> > explicit, with this change they become implicit. Not sure what we are
> > gaining here ??
> >
> >
> > In my humble opinion, having the error checking out of the way allows
> > the code reader to concentrate on the JNI code while maintaining error
> > checking. We use something similar internally, so perhaps I'm biased to
> > it :-).
> > If this is not a desired/helpful "feature" to simplify tests in general,
> > I will backtrack it and just add the explicit tests to the native code
> > of the locks for the fix
> > https://bugs.openjdk.java.net/browse/JDK-8191519 instead.
> >
> > Let me however try to make my case and let me know what you all think!
> >
> >
> > > If agreed with this, we can augment the SafeJNIEnv class as
> needed.
> > > Also, if the tests require something else than fatal errors, we
> > can add
> > > a different marker and make it a parameter to the base class.
> > >
> > > Webrev: http://cr.openjdk.java.net/~jcbeyler/8210842/webrev.00/
> > <http://cr.openjdk.java.net/%7Ejcbeyler/8210842/webrev.00/>
> > > <http://cr.openjdk.java.net/%7Ejcbeyler/8210842/webrev.00/>
> > > Bug: https://bugs.openjdk.java.net/browse/JDK-8210842
> > >
> > > Let me know what you think,
> >
> > Two initial suggestions:
> >
> > 1. FatalOnException should be constructed with a description string
> so
> > that it can report the failing operation when calling FatalError
> rather
> > than the general "Problem with a JNI call".
> >
> >
> > Agreed with you, the new webrev produces:
> >
> > FATAL ERROR in native method: GetObjectClass
> > at
> nsk.share.gc.lock.CriticalSectionTimedLocker.criticalSection(CriticalSectionTimedLocker.java:47)
> > at
> nsk.share.gc.lock.jniref.JNIGlobalRefLocker.criticalNative(Native Method)
> > at
> nsk.share.gc.lock.jniref.JNIGlobalRefLocker.criticalSection(JNIGlobalRefLocker.java:44)
> > at
> nsk.share.gc.lock.CriticalSectionLocker$1.run(CriticalSectionLocker.java:56)
> > at java.lang.Thread.run(java.base at 12-internal/Thread.java:834)
> >
> >
> > and for a return NULL in NewGlobalRef, we would get automatically:
> >
> > FATAL ERROR in native method: NewGlobalRef:Return is NULL
> > at
> nsk.share.gc.lock.jniref.JNIGlobalRefLocker.criticalNative(Native Method)
> >
> > at
> >
> nsk.share.gc.lock.jniref.JNIGlobalRefLocker.criticalSection(JNIGlobalRefLocker.java:44)
>
> >
> >
> >
> > Again as we port and simplify more tests (I'll only do the locks for now
> > and we can figure out the next steps as start working on moving tests
> > out of vmTestbase),
> > we can add, if needed, other exception handlers that don't throw or do
> > other things depending on the JNI method outputs.
> >
> >
> > 2. Make the local SafeJNIEnv a pointer called env so that the change
> is
> > less disruptive. All the env->op() calls will remain and only the
> local
> > error checking will be removed.
> >
> >
> > Done, I used a unique_ptr to make the object created/destroyed/available
> > as a pointer do-able in one line:
> > std::unique_ptr<SafeJNIEnv> env(new SafeJNIEnv(jni_env));
> >
> > and then you can see that, as you mentioned, the disruption to the code
> > is much less:
> >
> http://cr.openjdk.java.net/~jcbeyler/8210842/webrev.01/test/hotspot/jtreg/vmTestbase/nsk/share/gc/lock/jniref/JNIGlobalRefLocker.cpp.udiff.html
> > <
> http://cr.openjdk.java.net/%7Ejcbeyler/8210842/webrev.01/test/hotspot/jtreg/vmTestbase/nsk/share/gc/lock/jniref/JNIGlobalRefLocker.cpp.udiff.html
> >
> >
> > Basically the tests now become internal to the SafeJNIEnv and the code
> > now only contains the JNI calls happening but we are protected and will
> > fail any test that has an exception or a NULL return for the call. Of
> > course, this is not 100% proof in terms of not having any error handling
> > in the test but in some cases like this, the new code seems to just work
> > better:
> >
> >
> http://cr.openjdk.java.net/~jcbeyler/8210842/webrev.01/test/hotspot/jtreg/vmTestbase/nsk/share/gc/lock/jniref/JNIGlobalRefLocker.cpp.html
> > <
> http://cr.openjdk.java.net/%7Ejcbeyler/8210842/webrev.01/test/hotspot/jtreg/vmTestbase/nsk/share/gc/lock/jniref/JNIGlobalRefLocker.cpp.html
> >
> >
> >
> >
> > The switch from, e.g., checking NULL returns to checking for pending
> > exceptions, need to be sure that the JNI operations clearly specify
> > that
> > NULL implies there will be an exception pending. This change may be
> an
> > issue for static code analysis if not smart enough to understand the
> > RAII wrappers.
> >
> >
> > Agreed, I fixed it to be more strict and say: in normal test handling,
> > the JNI calls should never return NULL or throw an exception. This
> > should hold for tests I imagine but if not we can add a different call
> > verifier as we go.
> >
> >
> > Thanks,
> > David
> >
> > > Jc
> >
> >
> >
> > Let me know what you all think. When talking about it a bit, I had
> > gotten some interest to see what it would look like. Here it is :-). Now
> > if it is not wanted like I said, I can backtrack and just put the error
> > checks after each JNI call for all the tests as we are porting them.
> > Jc
>
--
Thanks,
Jc
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