JDK-8145371 ClassCastException thrown in LambdaFormEditor.getInCache

[Martin Buchholz]

No takers? ... let's try again.  Despite uniform failure to reproduce this
except under a debugger, let's apply the simple obviously correct fix,
namely:

     /** Craft a LambdaForm customized for this particular MethodHandle */
     /*non-public*/
     void customize() {
+        final LambdaForm form = this.form;
         if (form.customized == null) {
             LambdaForm newForm = form.customize(this);
             updateForm(newForm);




On Wed, Jan 3, 2018 at 1:51 PM, Martin Buchholz <martinrb at google.com> wrote:

> Let's try again without mail bounces ...
>
>
> On Wed, Jan 3, 2018 at 1:40 PM, Martin Buchholz <martinrb at google.com>
> wrote:
>
>> Here at Google we tried to fix JDK-8145371 because it looked like it was
>> causing rare problems in production.  But after looking at the code, I'm
>> not sure...  Anyways,
>>
>> http://cr.openjdk.java.net/~martin/webrevs/jdk/MethodHandle.form/
>> https://bugs.openjdk.java.net/browse/JDK-8145371
>> Copying to a local in customize() must be an improvement.
>> The UNSAFE publication in updateForm looks fishy, as does that comment
>> in MethodHandleImpl.java.  Is there something the fullFence() is supposed
>> to do that isn't taken care of by putObjectVolatile ?
>>
>> Feel free to take ownership of this bug from me.
>>
>> --- a/src/java.base/share/classes/java/lang/invoke/MethodHandle.java
>> +++ b/src/java.base/share/classes/java/lang/invoke/MethodHandle.java
>> @@ -1660,13 +1660,13 @@
>>          assert(newForm.customized == null || newForm.customized == this);
>>          if (form == newForm)  return;
>>          newForm.prepare();  // as in MethodHandle.<init>
>> -        UNSAFE.putObject(this, FORM_OFFSET, newForm);
>> -        UNSAFE.fullFence();
>> +        UNSAFE.putObjectVolatile(this, FORM_OFFSET, newForm);
>>      }
>>
>>      /** Craft a LambdaForm customized for this particular MethodHandle */
>>      /*non-public*/
>>      void customize() {
>> +        final LambdaForm form = this.form;
>>          if (form.customized == null) {
>>              LambdaForm newForm = form.customize(this);
>>              updateForm(newForm);
>> diff --git a/src/java.base/share/classes/java/lang/invoke/MethodHandleImpl.java b/src/java.base/share/classes/java/lang/invoke/MethodHandleImpl.java
>> --- a/src/java.base/share/classes/java/lang/invoke/MethodHandleImpl.java
>> +++ b/src/java.base/share/classes/java/lang/invoke/MethodHandleImpl.java
>> @@ -909,7 +909,7 @@
>>              int c = count;
>>              maybeCustomizeTarget();
>>              if (c <= 1) {
>> -                // Try to limit number of updates. MethodHandle.updateForm() doesn't guarantee LF update visibility.
>> +                // Try to limit number of updates.
>>                  if (isCounting) {
>>                      isCounting = false;
>>                      return true;
>>
>>
>>
>