On Wed, 19 Jan 2022 05:47:57 GMT, Ioi Lam <ik...@openjdk.org> wrote: >> **Background:** >> >> In the Java Language, Enums can be tested for equality, so the constants in >> an Enum type must be unique. Javac compiles an enum declaration like this: >> >> >> public enum Day { SUNDAY, MONDAY ... } >> >> >> to >> >> >> public class Day extends java.lang.Enum { >> public static final SUNDAY = new Day("SUNDAY"); >> public static final MONDAY = new Day("MONDAY"); ... >> } >> >> >> With CDS archived heap objects, `Day::<clinit>` is executed twice: once >> during `java -Xshare:dump`, and once during normal JVM execution. If the >> archived heap objects references one of the Enum constants created at dump >> time, we will violate the uniqueness requirements of the Enum constants at >> runtime. See the test case in the description of >> [JDK-8275731](https://bugs.openjdk.java.net/browse/JDK-8275731) >> >> **Fix:** >> >> During -Xshare:dump, if we discovered that an Enum constant of type X is >> archived, we archive all constants of type X. At Runtime, type X will skip >> the normal execution of `X::<clinit>`. Instead, we run >> `HeapShared::initialize_enum_klass()` to retrieve all the constants of X >> that were saved at dump time. >> >> This is safe as we know that `X::<clinit>` has no observable side effect -- >> it only creates the constants of type X, as well as the synthetic value >> `X::$VALUES`, which cannot be observed until X is fully initialized. >> >> **Verification:** >> >> To avoid future problems, I added a new tool, CDSHeapVerifier, to look for >> similar problems where the archived heap objects reference a static field >> that may be recreated at runtime. There are some manual steps involved, but >> I analyzed the potential problems found by the tool are they are all safe >> (after the current bug is fixed). See cdsHeapVerifier.cpp for gory details. >> An example trace of this tool can be found at >> https://bugs.openjdk.java.net/secure/attachment/97242/enum_warning.txt >> >> **Testing:** >> >> Passed Oracle CI tiers 1-4. WIll run tier 5 as well. > > Ioi Lam has updated the pull request incrementally with one additional commit > since the last revision: > > Use InstanceKlass::do_local_static_fields for some field iterations
Looks good. Minor comment below. Also, several files with copyright year 2021 need updating. src/hotspot/share/cds/cdsHeapVerifier.cpp line 63: > 61: // class Bar { > 62: // // this field is initialized in both CDS dump time and runtime. > 63: // static final Bar bar = new Bar; `new Bar` should be `new Bar()`? ------------- Marked as reviewed by ccheung (Reviewer). PR: https://git.openjdk.java.net/jdk/pull/6653