The basic problem is that we are relying on undefined behaviour, as documented in the code:
// This whole business of passing information from ResourceObj::operator new // to the ResourceObj constructor via fields in the "object" is technically UB. // But it seems to work within the limitations of HotSpot usage (such as no // multiple inheritance) with the compilers and compiler options we're using. // And it gives some possibly useful checking for misuse of ResourceObj. I am removing the undefined behaviour by passing the type of allocation through a thread local variable. This solution has some advantages: 1) it is not UB 2) it is simpler and easier to understand 3) it uses less memory (I could make it use even less if I made the enum `allocation_type` a u8) 4) in the *very* unlikely situation that stack memory (or embedded) already equals the data calculated from the address of the object, the code will also work. When doing the change, I also updated `allocated_on_stack()` to the new name `allocated_on_stack_or_embedded()` which is much harder to misinterpret. I also disallow to "fake" the memory type by explicitly calling `ResourceObj::set_allocation_type`. This forced me to change two places that is faking the allocation type of an embedded `GrowableArray` from `STACK_OR_EMBEDDED` to `C_HEAP`. The faking of the type is hard to understand as a `STACK_OR_EMBEDDED` `GrowableArray` can allocate any type of object. My guess is that `GrowableArray` has changed behaviour, or maybe that it was hard to understand because the old naming of `allocated_on_stack()`. I have also tried to update the comments. In doing that I not only changed the comments for this change, but also for the *incorrect* advice to always delete object you allocate with new. Testing on debug build tier1-3 Testing on release build tier1 ------------- Commit messages: - 8269537: memset() is called after operator new Changes: https://git.openjdk.java.net/jdk/pull/5387/files Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5387&range=00 Issue: https://bugs.openjdk.java.net/browse/JDK-8269537 Stats: 109 lines in 8 files changed: 1 ins; 66 del; 42 mod Patch: https://git.openjdk.java.net/jdk/pull/5387.diff Fetch: git fetch https://git.openjdk.java.net/jdk pull/5387/head:pull/5387 PR: https://git.openjdk.java.net/jdk/pull/5387
