[jdk17] RFR: 8269240: java/foreign/stackwalk/TestAsyncStackWalk.java test failed with concurrent GC [v3]

Jorn Vernee jvernee at openjdk.java.net
Thu Jul 15 15:58:16 UTC 2021

On Thu, 15 Jul 2021 15:54:50 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> This patch rewrites the prologue and epilogue of panama upcalls, in order to fix the test failure from the title.
>> Previously, we did a call to potentially attach the current thread to the VM, and then afterwards did the same suspend and stack reguard checks that we do on the back-edge of a native downcall. Then, on the back edge of the upcall we did another conditional call to detach the thread.
>> The suspend and reguard checks on the front-edge are incorrect, so I've changed the 2 calls to mimic what is done by JavaCallWrapper instead (with attach and detach included), and removed the old suspend and stack reguard checks.
>> FWIW, this removes the JavaFrameAnchor save/restore MacroAssembler code. This is now written in C++. Also, MacroAssembler code was added to save/restore the result of the upcall around the call on the back-edge, which was previously missing. Since the new code allocates a handle block as well, I've added handling for those oops to frame & OptimizedUpcallBlob.
>> Testing: local running of `jdk_foreign` on Windows and Linux (WSL). Tier 1-3
> Jorn Vernee has updated the pull request incrementally with one additional commit since the last revision:
>   Address David's review comments

David, I've addressed your review comments.

For now I went with changing the return type of `on_entry` to `JavaThread*`, assuming the potential pointer conversion is not an issue. 

I tried for a while to implement a static assert to check that `Thread*` is trivial convertible to `JavaThread*` as well, but couldn't find a way to do that at compile time, so left it for now. It looks like C++ 20 has a type trait to check this: https://en.cppreference.com/w/cpp/types/is_pointer_interconvertible_base_of (I think this does what we want). I thought maybe we could just mimic the reference implementation, but looking at for instance the MSVC STL implementation, this type trait is implemented as a compiler intrinsic, so I think we'll have to wait until we are on C++ 20 before adding such a static assert.


PR: https://git.openjdk.java.net/jdk17/pull/149

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