[14] RFR (S): 8234401: ConstantCallSite may stuck in non-frozen state

[Paul Sandoz]

Ah the perils of partial construction :-)

Subtle, so I could be misunderstanding something, did you intend to remove the assignment of isFrozen in the ConstantCallSite constructor?

ConstantCallSite:

     protected ConstantCallSite(MethodType targetType, MethodHandle createTargetHook) throws Throwable {

-        super(targetType, createTargetHook);
-        isFrozen = true;
+        super(targetType, createTargetHook); // "this" instance leaks into createTargetHook
+        UNSAFE.storeStoreFence(); // properly publish isFrozen

     }

Paul.

> On Nov 19, 2019, at 8:53 AM, Vladimir Ivanov <vladimir.x.ivanov at oracle.com> wrote:
> 
> http://cr.openjdk.java.net/~vlivanov/8234401/webrev.00/
> https://bugs.openjdk.java.net/browse/JDK-8234401
> 
> ConstantCallSite has a ctor which deliberately leaks partially initialized instance into user code. isFrozen is declared final and if user code is obstinate enough, it can end up with non-frozen state embedded into the generated code. It manifests as a ConstantCallSite instance which is stuck in non-frozen state.
> 
> I switched isFrozen from final to @Stable, so non-frozen state is never constant folded. Put some store-store barriers along the way to restore final field handling.
> 
> I deliberately stopped there (just restoring isFrozen final field behavior). Without proper synchronization, there's still a theoretical possibility of transiently observing a call site in non-frozen state right after ctor is over. But at least there's no way anymore to accidentally break an instance in such a way it becomes permanently unusable.
> 
> PS: converted CallSite.target to final along the way and made some other minor refactorings.
> 
> Testing: regression test, tier1-2
> 
> Best regards,
> Vladimir Ivanov