I'm attempting to specify a list of directories to load custom .so files from and it seems Houdini Engine just doesn't care about HOUDINI_DSO_PATH. It will load custom .so's but it only seems to load ones that are located in /dso directories of paths listed in HOUDINI_PATH.

For example, having this path in HOUDINI_DSO_PATH will not load the .so files inside it.
/dd/tools/cent6_64/package/openvdb/3.0.0_beta01/houdini/13.0.524/dso

If I strip off the dso folder and stick this path into HOUDINI_PATH things are loaded correctly.
/dd/tools/cent6_64/package/openvdb/3.0.0_beta01/houdini/13.0.524

https://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=30710 [sidefx.com]

I just modified the behavior of this a bit, so that it works better together with Houdini. Houdini Engine will no longer overwrite HOUDINI_OTLSCAN_PATH and HOUDINI_DSO_PATH. Instead of overwrite, it'll insert the extra paths that are specified by the host into those environments variables. This means that you can specify the paths entirely as you would with Houdini, without needing to use the HAPI_*. (And this is probably what Houdini users would expect.)

But depending on the host, the host can still supply extra paths to Houdini Engine. And the extra paths will be inserted into the environment variables. In Maya's case, this is done by setting the HAPI_OTL_PATH and HAPI_DSO_PATH environment variables. The HAPI_* don't seem very useful in Maya's case now. I was tempted to remove them to simplify things, but I kept them around for compatibility. If anyone has a use case for them (instead setting the HOUDINI_* versions), I'm interested to hear about it.

Hey Andrew, I am currently testing 13.0.532 and noticed I started having an issue where houdini_otlscan_path is set always to & in the engine regardless of what my houdini.env file has.. could that be the reason why? (I am pushing to update us to the latest and greatest with the python GIL fix, so I am wondering whether that would fix this issue as well)

Yeah, this is most likely what's happening. Before the changes mentioned above, you would have had to set HAPI_OTL_PATH. And Houdini Engine will use that to set HOUDINI_OTLSCAN_PATH.