HHVM 3.19 has added something called CLI server mode: https://hhvm.com/blog/2017/04/13/hhvm-3-19.html
The idea of the CLI server is that some caches can be shared and that the startup costs of HHVM can be avoided. The documentation has no information about how to run it unfortunately: https://docs.hhvm.com/hhvm/advanced-usage/CLI-server
The actual code for the CLI-server can be found here: https://github.com/facebook/hhvm/blob/master/hphp/runtime/server/cli-server.cpp
But I see no callable endpoints and I can't find any other documentation about it online. So... who's got an example of how to call it?