[OpenJDK 2D-Dev] Question regarding the integration of harfbuzz (JEP 258)

[Volker Simonis]

Hi,

the integration of harfbuzz broke our AIX build because there's no
implementation available for the hb_atomic macros in
hb-atomic-private.hh. I've fixed that locally but still get a crash
when running a simple AWT program (even with
-Dsun.font.layoutengine=icu).

I'm curretnly debugging the problem, but I have some general questions:

1. Do we really need the multi-threaded features of harfbuzz in OpenJDK?

2. Why does hurbuzz require these synchronization macros? From a first
glance it doesn't seem to use multiple threads by itself. Does it have
some global data structures which it needs to protect if harfbuzz is
called from various threads?

3. Is there a way to test the hurfbuzz engine on a new platform? I saw
the new test TestLayoutVsICU.java but it is marked as "manual" and it
seems to require external fonts (at least some of which seem to be
freely available). Could you please provide at least a minimal
description on how this test can be run?

4. Is there a way to test that the implementation of the hb_atomic
macros in hb-atomic-private.hh is correct (i.e. a way to stress
harfbuzz from multiple threads)? I think this is important as I
couldn't find a good description of the requirements for the atomic
macros and on weak memory model architectures we should really get
this right. For example there's no description of which fences are
required around the various atomic operations. Getting this right
across all platforms in the HotSpot (see
hotspot/src/os_cpu/../vm/atomic_os_cp.inline.hpp) is already hard
enough so I'm a little concerned that we are now introducing similar
primitives in the class library.

Thank you and best regards,
Volker