> **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 with a new target base due to a merge or a rebase. The pull request now contains 10 commits: - fixed copyright year - Merge branch 'master' into 8275731-heapshared-enum - fixed whitespace - Fixed comments per @calvinccheung review - Merge branch 'master' into 8275731-heapshared-enum - Use InstanceKlass::do_local_static_fields for some field iterations - Merge branch 'master' into 8275731-heapshared-enum - added exclusions needed by "java -Xshare:dump -ea -esa" - Comments from @calvinccheung off-line - 8275731: CDS archived enums objects are recreated at runtime ------------- Changes: https://git.openjdk.java.net/jdk/pull/6653/files Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6653&range=06 Stats: 860 lines in 16 files changed: 807 ins; 4 del; 49 mod Patch: https://git.openjdk.java.net/jdk/pull/6653.diff Fetch: git fetch https://git.openjdk.java.net/jdk pull/6653/head:pull/6653 PR: https://git.openjdk.java.net/jdk/pull/6653