8u60 backport RFR (M) 8067662: "java.lang.NullPointerException: Method name is null" from StackTraceElement.<init>

[Coleen Phillimore]

I see.  The PreviousVersionWalker is gone in 9 and you're using it to 
find the method.

But this is only going to find the method if it happens to be in the 
cpCache somewhere.   I think 
pv_node->prev_constant_pool()->pool_holder() is scratch_class (not 100% 
sure).  In which case, you can look at that class to find the method 
with idnum.

Coleen

On 4/7/15, 1:09 AM, serguei.spitsyn at oracle.com wrote:
> Coleen,
>
> Thank you for looking at this!
>
> The main difference is in instanceKlass.cpp and instanceKlass.hpp.
>
> 8u60:
> +Method* InstanceKlass::method_with_orig_idnum(int idnum) {
> +  if (idnum >= methods()->length()) {
> +    return NULL;
> +  }
> +  Method* m = methods()->at(idnum);
> +  if (m != NULL && m->orig_method_idnum() == idnum) {
> +    return m;
> +  }
> +  // Obsolete method idnum does not match the original idnum
> +  for (int index = 0; index < methods()->length(); ++index) {
> +    m = methods()->at(index);
> +    if (m->orig_method_idnum() == idnum) {
> +      return m;
> +    }
> +  }
> +  // None found, return null for the caller to handle.
> +  return NULL;
> +}
> +
> +
> +Method* InstanceKlass::method_with_orig_idnum(int idnum, int version) {
> +  if (constants()->version() == version) {
> +    return method_with_orig_idnum(idnum);
> +  }
> +  ConstantPoolCache* cp_cache = NULL;
> +  PreviousVersionWalker pvw(Thread::current(), (InstanceKlass*)this);
> +  for (PreviousVersionNode * pv_node = pvw.next_previous_version();
> +       pv_node != NULL; pv_node = pvw.next_previous_version()) {
> +    ConstantPool* prev_cp = pv_node->prev_constant_pool();
> +    if (prev_cp->version() == version) {
> +      cp_cache = prev_cp->cache();
> +      break;
> +    }
> +  }
> +  if (cp_cache == NULL) {
> +    return NULL; // The pv_node is gone, no method is found
> +  }
> +  Method* method = NULL;
> +  for (int i = 0; i < cp_cache->length(); i++) {
> +    ConstantPoolCacheEntry* entry = cp_cache->entry_at(i);
> +    method = entry->get_interesting_method_entry(this);
> +    if (method == NULL) {
> +      continue; // skip uninteresting entries
> +    }
> +    if (method->orig_method_idnum() == idnum) {
> +      return method;
> +    }
> +  }
> +  // None found, return null for the caller to handle.
> +  return NULL;
> +}
>
>
> jdk 9:
>
> +Method* InstanceKlass::method_with_orig_idnum(int idnum) {
> +  if (idnum >= methods()->length()) {
> +    return NULL;
> +  }
> +  Method* m = methods()->at(idnum);
> +  if (m != NULL && m->orig_method_idnum() == idnum) {
> +    return m;
> +  }
> +  // Obsolete method idnum does not match the original idnum
> +  for (int index = 0; index < methods()->length(); ++index) {
> +    m = methods()->at(index);
> +    if (m->orig_method_idnum() == idnum) {
> +      return m;
> +    }
> +  }
> +  // None found, return null for the caller to handle.
> +  return NULL;
> +}
> +
> +
> +Method* InstanceKlass::method_with_orig_idnum(int idnum, int version) {
> +  InstanceKlass* holder = get_klass_version(version);
> +  if (holder == NULL) {
> +    return NULL; // The version of klass is gone, no method is found
> +  }
> +  Method* method = holder->method_with_orig_idnum(idnum);
> +  return method;
> +}
>
>
> Thanks,
> Serguei
>
>
> On 4/6/15 6:49 PM, Coleen Phillimore wrote:
>>
>> This backport looks good.  Why didn't the patch apply cleanly? It 
>> seems mostly the same to me.
>> Thanks,
>> Coleen
>>
>> On 4/6/15, 7:50 PM, serguei.spitsyn at oracle.com wrote:
>>> Coleen and Dan,
>>>
>>> I'm asking you as the jdk  9 reviewers...
>>>
>>> Please, let me know if you have any chance and plans to review this.
>>> Would it be enough to have just one (R) reviewer for a non-clean 
>>> backport?
>>>
>>> Thanks,
>>> Serguei
>>>
>>>
>>>
>>> On 4/2/15 5:03 PM, serguei.spitsyn at oracle.com wrote:
>>>> Please, review the jdk 8u60 backport for:
>>>> https://bugs.openjdk.java.net/browse/JDK-8067662
>>>>
>>>> 8u60 hotspot webrev:
>>>> http://cr.openjdk.java.net/~sspitsyn/webrevs/2015/hotspot/8067662-JVMTI-trace.8u60 
>>>>
>>>>
>>>> 8u60 webrev for unit test update (the fix applies cleanly):
>>>> http://cr.openjdk.java.net/~sspitsyn/webrevs/2015/jdk/8067662-JVMTI-trace-test.8u60 
>>>>
>>>>
>>>>
>>>>
>>>> 9 hotspot webrev:
>>>> http://cr.openjdk.java.net/~sspitsyn/webrevs/2015/hotspot/8067662-JVMTI-trace.2 
>>>>
>>>>
>>>> 9 webrev for unit test update:
>>>> http://cr.openjdk.java.net/~sspitsyn/webrevs/2015/jdk/8067662-JVMTI-trace-test.2 
>>>>
>>>>
>>>>
>>>> Summary:
>>>>   The 9 fix can not be applied cleanly so that I have to rework the 
>>>> fix a little bit.
>>>>
>>>>   An NPE is trown in a thread dumping via JMX when doing CPU 
>>>> profiling in NetBeans Profiler and VisualVM.
>>>>   The issue is that the methods and related klass versions are not 
>>>> kept alive if a class redefinition
>>>>   takes place between catching a Throwable and taking a thread dump.
>>>>   It can result in loosing an obsolete method, and so, the 
>>>> reconstruction of method name becomes impossible.
>>>>   In such a case, the null reference is returned instead of a valid 
>>>> method name.
>>>>
>>>>   The solution is to use current klass version and method 
>>>> orig_idnum instead of ordinary method idnum
>>>>   to find required method pointer. In the worst case when the 
>>>> related klass version is gone
>>>>   (was not included to or was removed from the previous_versions 
>>>> linked list), a saved method name
>>>>   CP index of the latest klass version can be used to restore the 
>>>> method name.
>>>>   The footprint extra overhead for this approach is u2 per stack 
>>>> frame.
>>>>
>>>> Testing in progress:
>>>>   In progress: nsk redefine classes tests, JTREG java/lang/instrument
>>>>
>>>>
>>>> Thanks,
>>>> Serguei
>>>>
>>>
>>
>