[Note review on both core-libs and hotspot-gc-dev lists; try not to lose either when replying.]
Please review a new function: java.lang.ref.Reference.refersTo. This function is needed to test the referent of a Reference object without artificially extending the lifetime of the referent object, as may happen when calling Reference.get. Some garbage collectors require extending the lifetime of a weak referent when accessed, in order to maintain collector invariants. Lifetime extension may occur with any collector when the Reference is a SoftReference, as calling get indicates recent access. This new function also allows testing the referent of a PhantomReference, which can't be accessed by calling get. The new function uses a native method whose implementation is in the VM so it can use the Access API. It is the intent that this function will be intrinsified by optimizing compilers like C2 or graal, but that hasn't been implemented yet. Bear that in mind before rushing off to change existing uses of Reference.get. CR: https://bugs.openjdk.java.net/browse/JDK-8188055 https://bugs.openjdk.java.net/browse/JDK-8241029 (CSR) Webrev: https://cr.openjdk.java.net/~kbarrett/8188055/open.04/ Testing: mach5 tier1 Locally (linux-x64) verified the new test passes with various garbage collectors.
