Install only headers required by julia.h

[petercolberg]

Closes #17657

[tkelman]

these uv*.h aren't in src/support, they're done on a different line

[tkelman]

I think this would have less chance of going stale if we filtered out the specific ones we know we don't need. Or move them to a different location like src/support/include

[petercolberg]

I was thinking of actually testing the installed libjulia by building the embedding example:

cc -I/usr/include/julia -o embedding embedding.c -ldl -lrt -lpthread -lopenlibm -ljulia      
/tmp/cc660rPO.o: In function `main':
embedding.c:(.text+0x1c6): undefined reference to `jl_tls_states'
embedding.c:(.text+0x1e9): undefined reference to `jl_tls_states'
embedding.c:(.text+0x2fe): undefined reference to `jl_tls_states'
embedding.c:(.text+0x309): undefined reference to `jl_tls_states'
embedding.c:(.text+0x31a): undefined reference to `jl_tls_states'
collect2: error: ld returned 1 exit status

Any idea why the linker cannot find jl_tls_states?

[tkelman]

yeah #8757 has been open for a while. I think you need a -DJULIA_ENABLE_THREADING

[petercolberg]

Now the example compiles but fails to run:

./embedding 
ERROR: system image file "/home/peter/git/github.com/JuliaLang/julia/examples/../lib/x86_64-linux-gnu/julia/v0.5/sys.so" not found

Which variable sets the path to the system image?

[tkelman]

JULIA_HOME, are you setting that as an environment variable? If so you're setting it to the wrong location, or probably shouldn't be setting it at all.

[petercolberg]

It seems to work now:

JULIA_HOME=/usr ./embedding 
1.4142135623730951
sqrt(2.0) in C: 1.414214e+00
sqrt(2.0) in C: 1.414214e+00
x = [9.000000e+00 8.000000e+00 7.000000e+00 6.000000e+00 5.000000e+00 4.000000e+00 3.000000e+00 2.000000e+00 1.000000e+00 0.000000e+00 ]
my_func(5.0) = 10.000000
UndefVarError(:this_function_does_not_exist)

For the purpose of testing this is fine, but why is JULIA_HOME not set in libjulia.so?

[tkelman]

See

julia/src/init.c

Line 498 in 643bac8

jl_options.julia_home = getenv("JULIA_HOME");

, there's a getenv to allow you to point libjulia to use a different system image path if you don't have the command-line executable available - so exactly in the embedding case. A lot of people do seem to mistakenly set that variable to the wrong thing and Julia fails to start because of it, so we should document that better or pick a more specific name.

[petercolberg]

Have you thought about an include dir for public headers, separate from src and src/support?

[tkelman]

The install tree should look like that, but the source tree doesn't necessarily have to.

[petercolberg]

Indeed. It is suggestion to make the developer aware that these are public headers.

[yuyichao]

Do note that headers required by julia.h != public headers / public APIs. There are functions defined in those headers that are intentionally hidden yet the types defined in the same header are needed to define the ABI.

[tkelman]

My prior feedback is now collapsed at #17745 (comment) still applies, I don't like this form where JL_HEADERS needs to be kept up to date. A shorter exclusions list of things that are currently included in src/support/*.h but aren't needed would be more maintainable.