(11) RFR (S) JDK-8205509: assert(_name_and_id != 0LL) failed: encountered a class loader null name and id

[coleen.phillimore at oracle.com]

Lois,
This looks good!

http://cr.openjdk.java.net/~lfoltan/bug_jdk8205509/webrev/src/hotspot/share/classfile/classLoaderData.cpp.udiff.html

    if (!h_class_loader.is_null()) {
      _class_loader = _handles.add(h_class_loader());
    }
  
+ if (!h_class_loader.is_null()) {
+ _class_loader_klass = h_class_loader->klass();
+ }
+

Can you put the _class_loader_klass under the if statement above it?

+ } else {
+ return _class_loader_klass->external_name();

Can you add short comment:  // May be called in a race before 
_name_and_id is initialized.

Unfortunately, there isn't a good way to assert this (other than maybe a 
flag which would serve the same purpose as a null _name_and_id), and 
this code path is sensitive to safepoints because the link from 
class_loader to ClassLoaderData and the addition of ClassLoaderData to 
the CLDG needs to appear atomic.

Thanks for the speedy fix.
Coleen

On 6/22/18 7:00 PM, Lois Foltan wrote:
> Please review the following change to address a hs-tier5 test failure. 
> The recent change for JDK-8202605 aggravated an existing race 
> condition within ClassLoaderDataGraph::add() where a given class 
> loader's ClassLoaderData structure is added to the 
> ClassLoaderDataGraph prior to full initialization of the CLD's 
> _class_loader_klass, _name and _name_and_id fields within 
> ClassLoaderData::initialize_name_and_klass.  To ensure that methods 
> loader_name() and loader_name_and_id() always provide a string for the 
> class loader name, the fix involved moving the field, 
> _class_loader_klass, to the ClassLoaderData's constructor where if 
> _name and/or _name_and_id fields are null, a reasonable 
> _class_loader_klass's external_name() can be provided.
>
> open webrev http://cr.openjdk.java.net/~lfoltan/bug_jdk8205509/webrev/
> bug link at https://bugs.openjdk.java.net/browse/JDK-8205509
>
> Testing: hs-tier(1-2), jdk-tier(1-3) complete
>                hs-tier3-5 in progress
>                --test-repeat 50 ran for tier1 platforms of test 
> jdk/java/lang/instrument/DaemonThread/TestDaemonThread.java
>
> Thanks,
> Lois