JDK-8145371 ClassCastException thrown in LambdaFormEditor.getInCache

[John Rose]

That looks good to me.  Vladimir Ivanov should take a look.
Christmas vacation is just ending in Russia, so he should be around soon.

On Jan 8, 2018, at 6:41 PM, Martin Buchholz <martinrb at google.com> wrote:
> 
> 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 <mailto: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 <mailto: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/ <http://cr.openjdk.java.net/~martin/webrevs/jdk/MethodHandle.form/>
> https://bugs.openjdk.java.net/browse/JDK-8145371 <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;
> 
> 
>