RFR: 8305913: com/sun/jdi/JdbLastErrorTest.java failed with "'lastError = 42' missing from stdout/stderr" [v2]

[Kevin Walls]

On Sat, 15 Apr 2023 10:15:20 GMT, Kevin Walls <kevinw at openjdk.org> wrote:

>> This test is failing often since 8304725 added a call to Thread::current_in_asgct().  This can end up being called e.g. when resolving calls, and then the OS last error value is lost.
>> 
>> The test is reliable with a single warm-up call to getLastError.invoke() before the loop.
>> 
>> The test was introduced when in JDK-8292302 a change was undone that had made JavaThread::threadObj call Thread::current_or_null_safe, as the use of TLS upset this case of accessing last error directly.
>> 
>> This new Thread::current_in_asgct() case shows that the VM will find new ways to interfere with the last error value, or at least new VM code keeps wanting to call Thread::current.  This testcase is kind of niche usage, so it not an argument that VM code should not be calling Thread::current.   If this test is to stay active, it needs to have this warm-up getLastError call.  (If there are more issues, it might mean removing the test.)
>
> Kevin Walls has updated the pull request incrementally with one additional commit since the last revision:
> 
>   comment update feedback

Thanks for the comments and reviews - the updated Panama situation is that this test as written will still fail sometimes, but that is because the test is doing it wrong.  An actual call to the native GetLastError can still overwrite the last error value.  (Making a new call is likely to break the last error value just doing method resolution, at least the first time it happens.)

But the answer to the original problem is that we now have Linker.Option.CaptureCallState which gives us the chance to capture last error when calling a MethodHandle, and read the stored last error code in a VarHandle.  

I should remove the test, it is redundant, calling set/get last error directly is not the way to do this, and CaptureCallState is tested in test/jdk/java/foreign/capturecallstate/TestCaptureCallState.java

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PR Comment: https://git.openjdk.org/jdk/pull/13481#issuecomment-1533093670