[OpenJDK 2D-Dev] RFR: 8269223: -Xcheck:jni WARNINGs working with fonts on Linux

[Phil Race]

On Wed, 23 Jun 2021 09:19:16 GMT, Maxim Kartashev <github.com+28651297+mkartashev at openjdk.org> wrote:

> Added an `ExceptionCheck()` followed by `ExceptionDescribe()` and `ExceptionClear()` immediately after the Java calls made from the callback function `ReadTTFontFileFunc()` in `freetypeScaler.c`. 
> 
> The exception(s) need to be cleared because we're not returning immediately to Java that would've been able to handle them gracefully. And in order not to loose the exception entirely (even though the return value would also indicate an error condition), print out the exception with `ExceptionDescribe()` to aid in debugging.

src/java.desktop/share/native/libfontmanager/freetypeScaler.c line 53:

> 51:         (*(env))->ExceptionDescribe(env);\
> 52:         (*(env))->ExceptionClear(env);   \
> 53:     }

https://docs.oracle.com/en/java/javase/11/docs/specs/jni/functions.html#exceptiondescribe

"The pending exception is cleared as a side-effect of calling this function"

So you certainly don't need both of these and I would prefer that Describe only be used if really debugging where we think there's a REAL chance of an exception rather than just to keep JNI happy.

And the upcall that is likely (readBlock) itself will log any IOException (and catch it) in the event of an I/O error so I really think this is unlikely to be useful here.

src/java.desktop/share/native/libfontmanager/freetypeScaler.c line 198:

> 196:                                           sunFontIDs.ttReadBlockMID,
> 197:                                           bBuffer, offset, numBytes);
> 198:             // This is a callback, we are not returning immediately to Java and better report exceptions now

I think the comment is un-needed .. since the only reason to call CHECK_EXCEPTION() is because of this.
Same for the other case.

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PR: https://git.openjdk.java.net/jdk/pull/4572