Graph compatibility between machines

[nilsnolde]

Following #6688 (comment):

In which situations are OSRM graphs compatible with other machines (than they were produced on)? So far my understanding has been:

• no compat between commits/releases necessarily
• likely problems between architectures (i.e. x86 graph won't work on x64; or arm64 graph won't work on x64)
• compatibility of x64 across platforms, i.e. Linux x64 graphs run fine on Windows & Mac x64

Is the above more or less accurate? Or I can't expect Linux x64 graphs working on Windows x64? Or we don't really know and need to test?

[danpat]

I'm pretty sure that Linux<->Windows compatibility is 🚫 But it's been 20 years since I developed anything on Windows, so 🤷

Most systems these days are little endian, but different platforms have different ideas about the sizes of int and long types. Until we purge the codebase of those and stick to explicit std::uint32_t/etc, code compiled on Linux and Windows may generate different sizes for long.

The "Data models" section on this page shows some of the combinations:

https://en.cppreference.com/w/cpp/language/types

If you move between platforms with the same C++ data models, then I think things will work OK.

We have explicit checks in the code to prevent use of files between versions - files built with 5.25 won't work with osrm-routed from 5.26. This is by design, as we have no structure in the files to enable any easy forward/backward compatibility logic.

[nilsnolde]

Thanks @danpat. I'd be very interested to have cross-platform compatibility of the graph. Sounds like hell of a chore to convert the code base to use explicit types, but also a good way to get to know the code a bit better:)