Embedding Mono

The simplest way of embedding Mono is illustrated here:

int main (int argc, char *argv)
{
	/*
	 * Load the default Mono configuration file, this is needed
	 * if you are planning on using the dllmaps defined on the
	 * system configuration
	 */
	mono_config_parse (NULL);

	/*
	 * mono_jit_init() creates a domain: each assembly is
	 * loaded and run in a MonoDomain.
	 */
	MonoDomain *domain = mono_jit_init ("startup.exe");

	/*
	 * Optionally, add an internal call that your startup.exe
	 * code can call, this will bridge startup.exe to Mono
	 */
	mono_add_internal_call ("Sample::GetMessage", getMessage);

	/*
	 * Open the executable, and run the Main method declared
	 * in the executable
	 */
	MonoAssembly *assembly = mono_domain_assembly_open (domain, "startup.exe");

	if (!assembly)
		exit (2);
	/*
	 * mono_jit_exec() will run the Main() method in the assembly.
	 * The return value needs to be looked up from
	 * System.Environment.ExitCode.
	 */
	mono_jit_exec (domain, assembly, argc, argv);
}

/* The C# signature for this method is: string GetMessage () in class Sample */
MonoString*
getMessage ()
{
	return mono_string_new (mono_domain_get (), "Hello, world");
}

Internal Calls

The Mono runtime provides two mechanisms to expose C code to the CIL universe: internal calls and native C code. Internal calls are tightly integrated with the runtime, and have the least overhead, as they use the same data types that the runtime uses.

The other option is to use the Platform Invoke (P/Invoke) to call C code from the CIL universe, using the standard P/Invoke mechanisms.

To register an internal call, use this call you use the mono_add_internal_call routine.

P/Invoke with embedded applications

Unlike internal calls, Platform/Invoke is easier to use and more portable. It allows you to share code with Windows and .NET that have a different setup for internal calls to their own runtime.

Usually P/Invoke declarations reference external libraries like:

	[DllImport ("opengl")]
	void glBegin (GLEnum mode)
	

Mono extends P/Invoke to support looking up symbols not in an external library, but looking up those symbols into the same address space as your program, to do this, use the special library name "__Internal". This will direct Mono to lookup the method in your own process.

There are situations where the host operating system does not support looking up symbols on the process address space. For situations like this you can use the mono_dl_register_library.

mono_dl_register_library

Data Marshalling

Managed objects are represented as MonoObject* types. Those objects that the runtime consumes directly have more specific C definitions (for example strings are of type MonoString *, delegates are of type MonoDelegate* but they are still MonoObject *s).

As of Mono 1.2.x types defined in mscorlib.dll do not have their fields reordered in any way. But other libraries might have their fields reordered. In these cases, Managed structures and objects have the same layout in the C# code as they do in the unmanaged world.

Structures defined outside corlib must have a specific StructLayout definition, and have it set as sequential if you plan on accessing these fields directly from C code.

Important Internal calls do not provide support for marshalling structures. This means that any API calls that take a structure (excluding the system types like int32, int64, etc) must be passed as a pointer, in C# this means passing the value as a "ref" or "out" parameter.

Mono Runtime Configuration

Certain features of the Mono runtime, like DLL mapping, are available through a configuration file that is loaded at runtime. The default Mono implementation loads the configuration file from $sysconfig/mono/config (typically this is /etc/mono/config).

See the mono-config(5) man page for more details on what goes in this file.

The following APIs expose this functionality:

Function Pointers

To wrap a function pointer into something that the Mono runtime can consume, you should use the mono_create_ftnptr. This is only important if you plan on running on the IA64 architecture. Otherwise you can just use the function pointer address.

Advanced Execution Setups

These are not recommended ways of initializing Mono, they are done internally by mono_jit_init, but are here to explain what happens internally.