[cairo] concurrent text rendering issue

[cu]

Mikhail,

 In case you are wondering, we encountered similar issues when rendering
text on other platforms (MacOS and Linux). They occur slightly less
often than under Windows, but it happens under some conditions. The best
answer I've found so far is to lock all text operations. It seems that
it is helps more to lock text_extent and set font size ops, than the
actual text output.

 To the Cairo developers - it would be awesome if these text issues were
resolved, since locking necessarily takes a bite out of product performance.



Kozhevnikov Mikhail wrote:
> Hi All,
>
> I'm getting an error when renderig text concurrently on Windows.
>
> Here's the experiment: we render repeatedly a set of letters in different font sizes. Neither letters, nor font sizes change from iteration to iteration. If we do it with one thread, it works fine and we get consistent results. If we use more of them, the output varies - some letters are missing. Sometimes an out of memory error is reported. See the sample images and code attached (only unique images are stored).
>
> I've found out that it only happens on Windows. Thus I suspect that this issue has to do with WinAPI font selection mechanism. For example, if we confine ourselves to one single font size, we wouldn't experience any problems.
>
> Could anyone suggest a way to fix that? Should it be considered a bug at all?
>
> Thanks in advance,
> Mikhail.
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