JDK-8145371 ClassCastException thrown in LambdaFormEditor.getInCache (original) (raw)

John Rose john.r.rose at oracle.com
Tue Jan 9 06:49:19 UTC 2018

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. - UNSAFE.putObject(this, FORMOFFSET, newForm); - UNSAFE.fullFence(); + UNSAFE.putObjectVolatile(this, FORMOFFSET, 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;

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