FFI launcher

FFI (foreign-function-interface) service launcher executes services, compiled as shared libraries.

The approach is very useful as it allows to combine power of Rust and Tokio asynchronous runtime with any compiled programming language, which can output shared libraries for Linux and supports a standard C-style ABI.


The provided FFI service build is compiled dynamically and does not work on MUSL-based Linux systems (e.g. Alpine). Consider either building the service from source code or contact the product vendor for support.

Command-line arguments

Unlike other services, the launcher is configured with command-line arguments. This is because “config” field of the service parameters payload is passed to the loaded shared library.

The arguments are:

  • <LIBRARY_PATH> path to the shared library (absolute or relative to EVA ICS directory), mandatory

  • --command-queue-size <NUMBER> size of the bus command queue (default: 8192). Should be raised for services which have temporary load peaks. If the queue is full, commands coming from the service library are dropped with an error.

  • --blocking-fp turns on blocking frame processing. By default pub/sub bus frames are processed in background, which causes random processing ordering. If the ordering is important (e.g. a service watches state of an item, managed by another one), the option must be turned on. In this case frames are processed one-by-one and svc_on_frame method blocks the bus connection until finished.


Use the template EVA_DIR/share/svc-tpl/svc-tpl-ffi.yml:

# FFI service launcher
command: svc/eva-ffi /path/to/lib.so
  path: var/bus.ipc
  # The config is sent to the loaded module as-is

Create the service using eva-shell:

eva svc create custom.name /opt/eva4/share/svc-tpl/svc-tpl-ffi.yml

or using the bus CLI client:

cd /opt/eva4
cat DEPLOY.yml | ./bin/yml2mp | \
    ./sbin/bus ./var/bus.ipc rpc call eva.core svc.deploy -

(see eva.core::svc.deploy for more info)


The launcher itself provides no EAPI commons methods except the standard ones (“test”, “info” and “stop”). All other methods are proxied to the loaded service library.