RFR (XS) 8189766: whitebox failure with -Xcheck:jni

[David Holmes]

Thanks Lois!

David

On 30/05/2018 12:57 AM, Lois Foltan wrote:
> Looks good.
> Lois
> 
> On 5/29/2018 3:06 AM, David Holmes wrote:
>> bug: https://bugs.openjdk.java.net/browse/JDK-8189766
>> webrev: http://cr.openjdk.java.net/~dholmes/8189766/webrev/
>>
>> A WB_ENTRY already handles the pending JNI exception check by 
>> explicitly clearing it via a helper:
>>
>> #define WB_ENTRY(result_type, header) JNI_ENTRY(result_type, header) \
>>   ClearPendingJniExcCheck _clearCheck(env);
>>
>> #define WB_END JNI_END
>>
>> But the whitebox function then does e.g:
>>
>> WB_ENTRY(jobject, WB_GetBooleanVMFlag(JNIEnv* env, jobject o, jstring 
>> name))
>>   bool result;
>>   if (GetVMFlag <bool> (thread, env, name, &result, &JVMFlag::boolAt)) {
>>     ThreadToNativeFromVM ttnfv(thread); // can't be in VM when we call 
>> JNI
>>     return booleanBox(thread, env, result);
>>   }
>>   return NULL;
>> WB_END
>>
>> where booleanBox is defined eventually as:
>>
>> template <typename T>
>> static jobject box(JavaThread* thread, JNIEnv* env, Symbol* name, 
>> Symbol* sig, T value) {
>>   ResourceMark rm(thread);
>>   jclass clazz = env->FindClass(name->as_C_string());
>>   CHECK_JNI_EXCEPTION_(env, NULL);
>>   jmethodID methodID = env->GetStaticMethodID(clazz,
>>         vmSymbols::valueOf_name()->as_C_string(),
>>         sig->as_C_string());
>>   CHECK_JNI_EXCEPTION_(env, NULL);
>>   jobject result = env->CallStaticObjectMethod(clazz, methodID, value);
>>   CHECK_JNI_EXCEPTION_(env, NULL);
>>   return result;
>> }
>>
>> so we call JNI methods that will set the pending_jni_exception_check 
>> flag, but CHECK_JNI_EXCEPTION is defined as:
>>
>> #define CHECK_JNI_EXCEPTION_(env, value) \
>>   do { \
>>     JavaThread* THREAD = JavaThread::thread_from_jni_environment(env); \
>>     if (HAS_PENDING_EXCEPTION) { \
>>       return(value); \
>>     } \
>>   } while (0)
>>
>> which means it is not clearing the pending_jni_exception_check flag 
>> even though it is checking for exceptions!
>>
>> So we explicitly clear the flag. Trying to use the JNI 
>> ExceptionOccurred function fails as not all the methods that call 
>> CHECK_JNI_EXCEPTION are _thread_in_native.
>>
>> Testing (in progress):
>>          hotspot tier1 and tier2 with -Xcheck:jni
>>          regular CI testing
>>
>> Thanks,
>> David
>