RFR: 8323664: java/awt/font/JNICheck/FreeTypeScalerJNICheck.java still fails with JNI warning on some Windows configurations [v3]

[Alexey Ivanov]

On Mon, 29 Jan 2024 07:13:49 GMT, Christoph Langer <clanger at openjdk.org> wrote:

>> This picks up fixing the issue of [JDK-8276809](https://bugs.openjdk.org/browse/JDK-8276809) again. A fix had been integrated with #17224 but @prrace had concerns and so it was backed out.
>> 
>> I have now spent quite some thoughts into the problem and end up with the [initial commit](https://github.com/openjdk/jdk/pull/6306/commits/5d18a76cb967e9ede6394cbd6c28bb61facf785c) of #6306 as the most elegant and least intrusive solution.
>> 
>> Why is this?
>> 
>> The JNI warning we observe in the test is:
>> `[WARNING in native method: JNI call made without checking exceptions when required to from CallStaticVoidMethodV
>> 	at sun.awt.Win32GraphicsEnvironment.initDisplay(java.desktop at 22.0.1-internal/Native Method)
>> 	at sun.awt.Win32GraphicsEnvironment.initDisplayWrapper(java.desktop at 22.0.1-internal/Win32GraphicsEnvironment.java:95)
>> 	at sun.awt.Win32GraphicsEnvironment.<clinit>(java.desktop at 22.0.1-internal/Win32GraphicsEnvironment.java:63)
>>         ...
>>         at FreeTypeScalerJNICheck.runTest(FreeTypeScalerJNICheck.java:53)
>> 	at FreeTypeScalerJNICheck.main(FreeTypeScalerJNICheck.java:44)`
>> 
>> This happens because obviously the test FreeTypeScalerJNICheck runs with `-Xcheck:jni` and in the scenario where we're observing the warning, a missing exception check for the JNI call to `sun.awt.Win32GraphicsEnvironment::dwmCompositionChanged` at awt_Win32GraphicsEnv.cpp#L129
>> https://github.com/openjdk/jdk/blob/c5e72450966ad50d57a8d22e9d634bfcb319aee9/src/java.desktop/windows/native/libawt/windows/awt_Win32GraphicsEnv.cpp#L129 is airing up. Omitting the exception check would not be a problem if it could be guaranteed that after this call no other JNI->Java call was being made. But seemingly in this very particular configuration on some of our Windows servers, there must be JNI->Java calls that follow the call to `sun.awt.Win32GraphicsEnvironment::dwmCompositionChanged`, likely from the subsequent call to [initScreens](https://github.com/openjdk/jdk/blob/c5e72450966ad50d57a8d22e9d634bfcb319aee9/src/java.desktop/windows/native/libawt/windows/awt_Win32GraphicsEnv.cpp#L149) in `sun.awt.Win32GraphicsEnvironment::initDisplay`. https://github.com/openjdk/jdk/blob/8b6293f6bfb7b7628c6604e6c44401fc96d85cf4/src/java.desktop/windows/native/libawt/windows/awt_Win32GraphicsEnv.cpp#L141 Maybe the usual control flow would call the wrapping native method `DWMIsComposit
 ionEnabled()` from somewhere else initially such that the initialization of `Win32GraphicsEnvironment` would not go ...
>
> Christoph Langer has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision:
> 
>  - Move Exception Check to the right place
>  - Merge branch 'master' into JDK-8323664
>  - Changes to assertion function and test as discussed
>  - Revert "JDK-8323664"
>    
>    This reverts commit 32128744252d75104e0d19f5eb701ffdc7b3d417.
>  - Merge branch 'master' into JDK-8323664
>  - JDK-8323664

src/java.desktop/windows/native/libawt/windows/awt_Debug.cpp line 158:

> 156:     // be on the safe side and avoid JNI warnings by calling ExceptionCheck
> 157:     // an accumulated exception is not cleared
> 158:     env->ExceptionCheck();

So, this doesn't actually do anything but avoids JNI warnings, does it?

`AwtDebugSupport::AssertCallback` can be called *at any time*, hence calling JNI functions here is unsafe. Adding `env->ExceptionCheck()` doesn't change anything.

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PR Review Comment: https://git.openjdk.org/jdk/pull/17404#discussion_r1471297169