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

[Kevin Rushforth]

On Thu, 11 Jun 2020 17:48:16 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> 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.
>
> I think I see what you are trying to do, but there are a couple of problems it is causing. I attached a new test
> program to the JBS bug report, UnicodeTextTest2.java, which avoids any null (0) characters. That test runs fine today,
> and with the first version of your fix (the one without the Map), but causes assertion failures with the current
> version of the patch:  (java:32761): Pango-CRITICAL **: 10:37:09.535: pango_itemize: assertion 'length >= 0' failed
> (java:32761): Pango-CRITICAL **: 10:37:09.963: pango_itemize: assertion 'length >= 0' failed
> 
> I also sometimes get this:
> 
> #
> # A fatal error has been detected by the Java Runtime Environment:
> #
> #  SIGSEGV (0xb) at pc=0x00007f00456c2d78, pid=32761, tid=32778
> #
> # JRE version: Java(TM) SE Runtime Environment (14.0+36) (build 14+36-1461)
> # Java VM: Java HotSpot(TM) 64-Bit Server VM (14+36-1461, mixed mode, sharing, tiered, compressed oops, serial gc,
> linux-amd64) # Problematic frame:
> # C  [libglib-2.0.so.0+0x84d78]  g_utf8_offset_to_pointer+0x28
> 
> Phil is the expert here, so I'd like him to weigh in.

Given my observation with the `start` pointer, I think the `HashMap` as you are using it is fine. Do you think a
`LinkedHashMap` might be useful to preserve the iteration order? (since you only iterate it once in `dispose` it
probably doesn't matter).

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

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