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 <marti...@google.com> wrote:
> Let's try again without mail bounces ...
>
>
> On Wed, Jan 3, 2018 at 1:40 PM, Martin Buchholz <marti...@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;
>>
>>
>>
>
