Sphinx supports parallel builds, but the extension currently doesn't declare whether it supports it (I wouldn't see why not, our current build works fine with parallel building enabled):
WARNING: the canonical_sphinx extension does not declare if it is safe for parallel reading, assuming it isn't - please ask the extension author to check and make it explicit
WARNING: doing serial read
Sphinx supports parallel builds, but the extension currently doesn't declare whether it supports it (I wouldn't see why not, our current build works fine with parallel building enabled):