I’m new to USD and trying to understand the intended use of parts of
usdSchemaExamples. I can’t find an explanation in the docs.
Firstly, why is schema.usda installed under
share/usd/examples/plugin/usdSchemaExamples/resources/usdSchemaExamples/
when there’s already resources/generatedSchema.usda, which I thought
was sufficient? Is schema.usda still required for a non-codeless
schema?
Second, are there circumstances under which usdSchemaExamples.so is
dlopened?
Here’s where the confusion arises…
I can see the Python extension module _usdSchemaExamples.so links
against usdSchemaExamples.so (found relative to $ORIGIN).
python3 build_scripts/build_usd.py -v ~/dev/usd_build_default
cd ~/dev/usd_build_default
readelf -d ./lib/python/pxr/UsdSchemaExamples/_usdSchemaExamples.so | grep -e 'NEEDED.*Schema' -e RUNPATH
0x0000000000000001 (NEEDED) Shared library: [usdSchemaExamples.so]
0x000000000000001d (RUNPATH) Library runpath: [$ORIGIN/../../../../share/usd/examples/plugin:$ORIGIN/../../..:/home/craig/dev/usd_build_default/lib]
It’s been called usdSchemaExamples.so and placed under a plugin/
subdir, which suggests it’s a plug-in that’s dlopened by a core USD
library, rather than being called libusdSchemaExamples.so and living
under an lib/ subdir as I’d expect for a shared library that’s
explicitly linked to.
If I set PXR_PLUGINPATH_NAME to the resources dir,
TF_DEBUG=“PLUG_* TF_DLOPEN”, then usdview a test.usda containing an
Xform prim with the ParamsAPI schema applied, only the
generatedSchema.usda and plugInfo.json are loaded.
usdSchemaExamples.so is never dlopened, despite it being
“registered” as a “plugin”. The TF_DEBUG output, missing TfDlopen:
Will read plugin info /home/craig/dev/usd_build_default/share/usd/examples/plugin/usdSchemaExamples/resources/plugInfo.json
Did read plugin info /home/craig/dev/usd_build_default/share/usd/examples/plugin/usdSchemaExamples/resources/plugInfo.json
Registering shared library plugin 'usdSchemaExamples' at '/home/craig/dev/usd_build_default/share/usd/examples/plugin/usdSchemaExamples.so'.
According to strace, only the files for a “codeless schema” are opened:
strace -f -e trace=openat usdview ./test.usda 2>&1 | grep examples
[pid 20707] openat(AT_FDCWD, "/home/craig/dev/usd_build_default/share/usd/examples/plugin/usdSchemaExamples/resources/plugInfo.json", O_RDONLY) = 3
[pid 20707] openat(AT_FDCWD, "/home/craig/dev/usd_build_default/share/usd/examples/plugin/usdSchemaExamples/resources/generatedSchema.usda", O_RDONLY) = 22
Is usdSchemaExamples.so supposed to be dlopened at some point? Or
it’s only required by the Python module (_usdSchemaExamples.so) and
the Unix “lib” naming convention has been disregarded there for some
reason?
Adding to the confusion, there are other DSOs which are dlopened:
Loading plugin 'hgiGL'.
TfDlopen: [opening] '/home/craig/dev/usd_build_default/lib/libusd_hgiGL.so' (flag=2)...
TfDlopen: [opened] '/home/craig/dev/usd_build_default/lib/libusd_hgiGL.so' (handle=0x55f776173d60)
Loading plugin 'hdStorm'.
TfDlopen: [opening] '/home/craig/dev/usd_build_default/plugin/usd/hdStorm.so' (flag=2)...
TfDlopen: [opened] '/home/craig/dev/usd_build_default/plugin/usd/hdStorm.so' (handle=0x55f7773d46c0)
Despite being a “plugin” libusd_hgiGL.so is also required by other libs:
readelf -d ./lib/libusd_hdSt.so | grep 'NEEDED.*GL'
0x0000000000000001 (NEEDED) Shared library: [libusd_hgiGL.so]
So it seems the choice of lib/ vs plugin/ directory names and “lib” as
a soname prefix has no meaning anymore, and there’s no separation
between required/needed shared libraries and dlopened plug-ins in USD?
Thanks