The following intermittent build failure in on macOS, while building the ':graphics:ccMacFont' task, was spotted in a couple recent CI build jobs:

> Task :graphics:ccMacFont FAILED
...
FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':graphics:ccMacFont'.
> java.util.concurrent.ExecutionException

See the attached log file for the complete ':graphics:ccMacFont' portion of the build.

We recently re-enabled parallel compilation on macOS with the fix for JDK-8339505 by removing the workaround that forced NUM_COMPILE_THREAD to 1.

Parallel compilation had been disabled on macOS due to JDK-8089417, but I recently closed that as "cannot reproduce", after running a fair amount of testing, and also because the code in question that got the error is no longer in our repo (and the macOS compiler has been updated to clang, although I think that's not relevant).

It appears that it does still happen, just in a different font module. Since we get no errors or warnings from the compiler, one possibility is that the bug lies in the JavaFX build scripts that implement the parallel compilation for the native code in the graphics module.