Question/discussion about JDK-8129582

Itai itaisha at
Sun Mar 18 11:19:59 UTC 2018


In hopes of getting this bug fixed, I have made changes to
`PangoGlyphLayout` so that is only allocates the FT2 FontMap once, and uses
a `PlatformImpl.FinishListener` to unref it when the JavaFX platform exits.
Attached is the modified version of the file.
In my personal tests, depending on hardware used, there is a speedup of
between x2 and x10 in layout times, and scrolling large Lists/Tables feels
as snappy with CTL languages as with any other language.
For anyone wanting to test it, remember this bug only affects Linux, and
only CTL languages (such as Arabic, Farsi, Hebrew and Hindi).


On Sun, Jan 8, 2017 at 11:39 PM, Itai <itaisha at> wrote:

> I think I have found two problems. The first, and probably most critical
> one, is that a new PangoFontMap is created for every call of
> PangoGlyphLayout#layout. It is not entirely clear from the Pango
> documentation what the lifetime or intended usage of a PangoFontMap is, but
> I have found this comment in [1]:
> "But note that a PangoFontMap is a big expensive object. So, you
> *really* want to be using only one for your entire program.
> Frequently calling pango_ft2_font_map_new() is going kill
> the performance of your application."
> This seems to imply PangoFontMap is intended as a global (per display?)
> font cache. Indeed, creating only one PangoFontMap seems to improve
> performance drastically, although I'm not sure what is the best way to
> handle this object (i.e. when and how it should be re-used and freed), as
> it should probably (?) be held for the entire lifetime of the JavaFX
> application.
> The second problem is probably less significant, but could still
> theoretically hurt performance - it has to do with the usage of
> g_list_nth_data, which as per [2] has O(N) complexity, and is called once
> per item in the list, which yields O(N^2) complexity. Replacing it with
> linked-list traversal with g_list_next should reduce this back to O(N).
> I hope this information is clear enough. As I said I lack the overall
> understanding of the JavaFX platform to know where and how to manage a
> global object, such as PangoFontMap should apparently be, so I refrain from
> posting any patch that I know would be wrong.
> Regards,
> Itai.
> [1]:
> [2]:
> stable/glist.html.en
> On Sun, Jan 8, 2017 at 8:08 PM, Itai <itaisha at> wrote:
>> Thank you for the link, it's an interesting read indeed!
>> I wasn't really skipping layout, just using the much simpler layout used
>> by Latin scripts, but you are correct that this will break for anything
>> more complex - this has nothing to do with BiDi though, more to do with
>> complex layout elements (like diacritic or cantillation marks for Hebrew,
>> or general Arabic/Farsi text).
>> Indeed, this can't be a general solution, but I guess I was driven by
>> frustration.
>> I have tried some more configurations though, and found that on Windows
>> the loss of performance is much less noticeable, which seems to mean that
>> the problem is either:
>> 1. Pango is inherently slow / inherently slow when laying out BiDi text.
>> 2. JavaFX uses Pango in a sub-optimal / redundant way.
>> 3. The JNI / native calls to Pango are done in a sub-optimal way.
>> Option 1 can be easily debunked, as general Gnome/GTK applications run as
>> smoothly with BiDi text as with Latin / LTR text.
>> For options 2 and 3 I guess some more digging into the code must be done.
>> My understanding is that JNI calls are not likely to incur performance loss
>> to such a degree, unless very large amounts of memory are copied back and
>> forth between Java and native code, so I'll start by reading into the Pango
>> documentation and understanding the logic of PangoGlyphLayout.
>> If you have any input on this or believe my assumptions or conclusions
>> are wrong I'd be glad to hear. I realize you are all busy with the upcoming
>> 9 release, so I'll try to get as detailed a result as I can.
>> Regards,
>> Itai.
>> On Wed, Jan 4, 2017 at 8:44 PM, Phil Race <philip.race at> wrote:
>>> You can't skip layout just because it is bidi ..
>>> where here you are apparently implicitly meaning Hebrew.
>>> This might be apparently working but may not always work even
>>> for Hebrew and will be a disaster for Arabic.
>>> Here is a web page which talks about OTL (OpenType Layout) for Hebrew :
>>> I can't say offhand why this might be exclusive to FX.
>>> That test case would be handy.
>>> So this needs more analysis even if you found a way to limit this to
>>> specifically Latin+Hebrew.
>>> -phil.
>>> On 01/04/2017 10:32 AM, Itai wrote:
>>> Some quick-and-dirty thing I hacked now and seems to improve the
>>> performance drastically is something like:
>>> if (complex but not bidi) {
>>>    use GlyphLayout.
>>> } else if (bidi) {
>>>    use java.text.Bidi.reorderVisually to get visual glyph order, then
>>> use same implementation as non-bidi non-complex layout
>>> } else {
>>>    ...
>>> }
>>> Very minimal tests show it working correctly, and performance is 8-10
>>> times faster (on par with non-bidi text).
>>> Do you think this solution makes sense? Can you see any obvious
>>> pitfalls?
>>> If it seems OK I'll try some more tests and then work it into something
>>> clean enough to submit as a patch suggestion.
>>> On Wed, Jan 4, 2017 at 7:48 PM, Itai <itaisha at> wrote:
>>>> Thanks for replying.
>>>> I think I understand what you're saying about the cache. As for
>>>> complexity - I'm mostly working with text which is only in Hebrew, which
>>>> isn't complex as far as I understand the definition (no glyph "fusing" as
>>>> in Arabic or Farsi). I can work with minor performance drops, but when the
>>>> same window takes more than 10 times to show if it has Hebrew labels is a
>>>> lot more than minor - and this is exclusive to JavaFX, so it's not like
>>>> this problem is unsolvable.
>>>> Perhaps the caching is indeed not the correct solution, but maybe there
>>>> can be a way to simplify the layout in non-complex BiDi cases? Or optimize
>>>> PangoGlyphLayout.layout?
>>>> Thank you again for replying, I really hope this issue can see some
>>>> improvement.
>>>> On Wed, Jan 4, 2017 at 7:26 PM, Philip Race < <philip.race at>
>>>> philip.race at> wrote:
>>>>> The cache is a heuristic optimisation and whether it helps depends on
>>>>> how well that cache is used.
>>>>> It is a time-space trade-off and I'd expect it to show up as helping
>>>>> more in micro-benchmarks or
>>>>> text-intensive benchmarks which use the same text broken in the same
>>>>> way.
>>>>> Complex text layout is inherently slower and if you are doing a lot of
>>>>> it .. it will be slow .. and
>>>>> unless it is repeated a cache won't help.
>>>>> During start-up I'd *expect* that there isn't a lot of re-use going on.
>>>>> You would need to profile how often  the same text (and attributes)
>>>>> are passed through this code.
>>>>> If you could provide us a test case we could examine it too.
>>>>> If it were a real use case, then we'd move on to examine the
>>>>> feasibility of caching ...
>>>>> -phil.
>>>>> On 1/4/17, 9:19 AM, Itai wrote:
>>>>>> Recently JDK-8129582 [1] started really affecting me, with startup
>>>>>> speed
>>>>>> and overall responsiveness becoming really bad.
>>>>>> Digging into it, I have found most time is wasted in
>>>>>> com.sun.javafx.text.GlyphLayout.layout (as represented by
>>>>>> PangoGlyphLayout
>>>>>> on my Linux machine), which in turn is called
>>>>>> by com.sun.javafx.text.PrismTextLayout.shape, which has:
>>>>>>      if (run.isComplex()) {
>>>>>>              /* Use GlyphLayout to shape complex text */
>>>>>>              layout.layout(run, font, strike, chars);
>>>>>>      } else {
>>>>>>              ...
>>>>>>              if (layoutCache == null) {
>>>>>>               ...
>>>>>>               } else {
>>>>>>                ...
>>>>>>               }
>>>>>>      }
>>>>>> which to my very naive reading seems as if while non-complex (with
>>>>>> all BiDi
>>>>>> text considered complex) glyph runs are cached, complex runs are never
>>>>>> cached, which forces re-calculation every time.
>>>>>> I'm trying to read and understand this part better, but could it be
>>>>>> possible that this is the issue? How feasible would it be to have a
>>>>>> layout
>>>>>> cache for complex runs, or at least non-complex BiDi runs?
>>>>>> Thanks,
>>>>>> Itai.
>>>>>> [1]:

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