This group implement a partial support for the Nit FFI in the interpreter.

It compiles foreign code on demand into a dynamic library that is then loaded and executed.

Features

This FFI implementation is a proof of concept, it implements the light FFI and only a subset of the full FFI.

From the light FFI:

• Nested extern methods.
• Module level code blocks.
• Passage of primitive types.
• Extern classes and constructors.

From the full FFI:

• Static Nit types in C.
• Public code block propagation.
• The cflags and ldflags annotations.

Missing features: (Still TODO)

• Callback to Nit code.
• Support C++, Java and Objective-C.
• Reference pinning.
• Support the pkgconfig and extra_java_files annotations.

The shared library and its API

The generated shared library hold the compiled foreign code of a single module. It is generated a the first extern method invocation within the module.

The shared library also implements a standard API to be used by the interpreter. This API is compose of 2 main elements:

• A single data structure to pass Nit instances and primitive data types:

  typedef union nit_call_arg {
    long value_Int;
    int value_Bool;
    uint32_t value_Char;
    uint8_t value_Byte;
    int8_t value_Int8;
    int16_t value_Int16;
    uint16_t value_UInt16;
    int32_t value_Int32;
    uint32_t value_UInt32;
    double value_Float;
    void* value_Pointer;
  } nit_call_arg;
  

• Standardized entrypoints, one per extern method in the module. Their signature is composed of the number or arguments, a preallocated array of the arguments and a preallocated structure for the return value.

  int (*nit_foreign_lib_entry)(int argc, nit_call_arg *args, nit_call_arg *ret);
  

  Each entrypoints unpack the arguments and call the FFI implementation method. The return value is stored in the preallocated structure where the interpreter can retreive it.