cat out/feta-braces-a.otf-table out/feta-braces-b.otf-table out/feta-braces-c.otf-table out/feta-braces-d.otf-table out/feta-braces-e.otf-table out/feta-braces-f.otf-table out/feta-braces-g.otf-table out/feta-braces-h.otf-table out/feta-braces-i.otf-table > out/emmentaler-brace.otf-table
echo '(design_size . 20)' > out/emmentaler-brace.otf-gtable
echo feta-braces-d feta-braces-c feta-braces-i feta-braces-e feta-braces-h feta-braces-a feta-braces-g feta-braces-f feta-braces-b > out/emmentaler-brace.subfonts
printf 'emmentaler-brace' > out/emmentaler-brace.fontname
cd ./out && /usr/bin/fontforge -script emmentaler-11.pe
Copyright (c) 2000-2011 by George Williams.
Executable based on sources from 13:48 GMT 22-Feb-2011-ML-TtfDb.
Library based on sources from 13:48 GMT 22-Feb-2011.
Cannot open /usr/local/src/Music/lilypond-2.15.36/build/mf/out/feta11.pfb
The requested file, feta11.pfb, does not exist
MergeFonts: Can't find font: feta11.pfb
emmentaler-11.pe: line 17
make: *** [out/emmentaler-11.svg] Error 1
make: *** Waiting for unfinished jobs.....
This error is caused by the use of -jN option when compiling lilypond (I used this instruction: make -j4 all). I used that option in order to maximize CPU cores utilization, however, this option can lead the compilation process into race condition. In the case of lilypond compilation, feta11.pfb is needed by one of compilation thread/stream before other thread/stream compiles it. When I omitted the -jN option, the compilation was successful.
In conclusion, be careful when we use the -jN option. This option can make the compilation process faster because the compilation process uses more than one CPU core, however, the race condition can occur in some cases.