Using Pony from Python

Using Pony code from Python would be really useful. So here’s how to do it. This guide is based on Pony 0.37.0 built from source with Clang. Build config uses no special flags.

Project

Pony uses the parent directory name as the library/executable/project name. Let’s create our test project with

mkdir foo
cd foo

Pony library

This is the Pony code we would like to call from Python. Let’s name it lib.pony (prefix not important).

actor@ GreetCounter
  var counter: USize = 0

  new create() =>
    None

  fun val counter(): USize =>
    counter

  be greet() =>
    @printf[I32]("Hi. %d\n".cstring(), counter)
    counter = counter + 1

This needs to be compiled into a static library:

ponyc -l

This created foo.h and libfoo.a

Helper

Since there seems to be an issue with Pony 0.37.0 we need a little helper C file. Let’s name it helper.c

// https://github.com/ponylang/ponyc/issues/3464
void Main_runtime_override_defaults_oo(void* opt)
{
  (void)opt; // avoid warning/error about unused variable
  return;
}

Compiling

Let’s setup our build environement:

export PONYRT_INCLUDE=<PONYBUILDDIR>/src/libponyrt/
export PONYRT_COMMON=<PONYBUILDDIR>/src/common/
export PONYRT_LIB=<PONYBUILDDIR>/build/release/libponyrt-pic.a

And now the build command:

gcc -shared -o libfoo.so \
	-I. -I $PONYRT_INCLUDE -I $PONYRT_COMMON \
	-Wl,--whole-archive \
		$PONYRT_LIB \
		helper.c \
		libfoo.a \
	-Wl,--no-whole-archive \
	-lpthread -ldl

We now have libfoo.so. readelf -s libfoo.so should confirm we have exported GreetCounter* and pony_*

Usage

And now to use the shared library we have to import it with LoadLibrary and call some Pony runtime setup functions. Setting argtypes and restypes is also required. Let’s name it run.py.

from ctypes import *

lib = cdll.LoadLibrary('./libfoo.so')

lib.pony_init.argtypes = [c_int, c_char_p]
lib.GreetCounter_Alloc.restype = c_void_p
lib.GreetCounter_tag_greet_o__send.argtypes = [c_void_p]
lib.GreetCounter_val_counter_Z.argtypes = [c_void_p]

lib.pony_init(1, c_char_p(b'name')) # argc and argv
lib.pony_start(True, None, None)
ptr = lib.GreetCounter_Alloc()

for x in range(100):
    lib.GreetCounter_tag_greet_o__send(ptr)

# pony actors are async, give a moment for them to finish
time.sleep(0.1)

assert lib.GreetCounter_val_counter_Z(ptr) == 99

Extra

Final directory tree

The final directory tree should look like

foo$ tree
.
├── foo.h
├── helper.c
├── libfoo.a
├── libfoo.so
├── lib.pony
└── run.py

Building Pony

git clone https://github.com/ponylang/ponyc.git
cd ponyc
make libs
make configure
make build -j 8