RFR: 8246348: Crash in libpango on Ubuntu 20.04 with some unicode chars

[Johan Vos]

On Thu, 11 Jun 2020 00:12:39 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> This addresses https://bugs.openjdk.java.net/browse/JDK-8246348
>
> modules/javafx.graphics/src/main/java/com/sun/javafx/font/freetype/PangoGlyphLayout.java line 87:
> 
>> 86:
>> 87:     private Map<TextRun, Long> runUtf8 = new HashMap<>();
>> 88:     public void layout(TextRun run, PGFont font, FontStrike strike, char[] text) {
> 
> In order for this to work, each TextRun would need to be immutable (at least during the life of this PangoGlyphLayout)
> and there would need to be a 1-1 mapping between the TextRun and the string pointer, independent of anything else. Is
> this the case? I'm seeing some crashes in OSPango.g_utf8_offset_to_pointer when testing. I don't know if they are
> related to this or not.

I would assume that once the layout method is called, the TextRun won't change anymore. If it would change, the current
code might break as well, as the string pointer is currently cached. I agree though that this is a brittle approach.
What I'm basically doing here is store additional information (the number of unicode codepoints rather than the number
of UTF 16 chars, which can then be mapped to the string pointer pointing to the relevant substring) on the TextRun, but
since I didn't want to modify TextRun, that additional info is stored in this Map. I'd prefer modifying TextRun though.

-------------

PR: https://git.openjdk.java.net/jfx/pull/249