1 * Embedding the Mono runtime, preliminary version
3 This document describes how to embed the Mono runtime in your
4 application, and how to invoke CIL methods from C, and how to
7 Slides for Paolo's presentation at .NET ONE on the embedding
8 API are available here: <a
9 href="http://primates.ximian.com/~lupus/slides/embed">Hosting the Mono
10 Runtime</a>. You can also get his <a
11 href="http://primates.ximian.com/~lupus/slides/embed/Mono-0.01.tar.gz">sample
12 Mono module for Perl</a>
14 Authors: Paolo Molaro, Miguel de Icaza.
16 * Embedding the runtime.
18 Embedding the runtime consists of various steps:
21 * Compiling and linking the Mono runtime
23 * Initializing the Mono runtime
25 * Optionally expose C code to the C#/CIL universe.
29 These are discussed in detail next.
31 ** Compiling and Linking
33 To embed the runtime, you have to link your code against the
34 Mono runtime libraries. To do this, you want to pass the
35 flags returned by pkg-config to your compiler:
38 pkg-config --cflags --libs mono
44 gcc sample.c `pkg-config --cflags --libs mono`
47 You can separate the compilation flags from the linking flags, for
48 instance, you can use the following macros in your makefile:
51 CFLAGS=`pkg-config --cflags mono`
52 LDFLAGS=`pkg-config --libs mono`
55 ** Initializing the Mono runtime
57 To initialize the runtime, call mono_jit_init, like this:
62 domain = mono_jit_init ("domain-name");
65 That will return a MonoDomain where your code will be
66 executed. You can create multiple domains. Each domain is
67 isolated from the other domains and code in one domain will
68 not interfere with code in other domains. This is useful if
69 you want to host different applications in your program.
71 Then you can load an assembly containing code into the domain:
74 MonoAssembly *assembly;
76 assembly = mono_domain_assembly_open (domain, "file.dll");
81 In the above example, the contents of `file.dll' will be
82 loaded into the domain. This only loads the code, but it will
83 not execute anything yet. You can replace `file.dll' with
84 another transport file, like `file.exe'
86 To start executing code, you must invoke a method in the
87 assembly, or if you have provided a static Main method (an
88 entry point), you can use the convenience function:
91 retval = mono_jit_exec (domain, assembly, argc - 1, argv + 1);
94 If you want to invoke a different method, look at the
95 `Invoking Methods in the CIL universe' section later on.
97 ** Shutting down the runtime
99 To shutdown the Mono runtime, you have to clean up all the
100 domains that were created, use this function:
103 mono_jit_cleanup (domain);
106 ** Applications that use threads.
108 The Boehm GC system needs to catch your calls to the pthreads
109 layer, so in each file where you use pthread.h you should
110 include the <gc/gc.h> file.
112 * Exposing C code to the CIL universe
114 The Mono runtime provides two mechanisms to expose C code to
115 the CIL universe: internal calls and native C code. Internal
116 calls are tightly integrated with the runtime, and have the
117 least overhead, as they use the same data types that the
120 The other option is to use the Platform Invoke (P/Invoke) to
121 call C code from the CIL universe, using the standard P/Invoke
124 To register an internal call, use this call in the C code:
127 mono_add_internal_call ("Hello::Sample", sample);
130 Now, you need to declare this on the C# side:
134 using System.Runtime.CompilerServices;
140 [MethodImplAttribute(MethodImplOptions.InternalCall)]
141 extern static string Sample ();
145 Since this routine returns a string, here is the C definition:
151 return mono_string_new (mono_domain_get (), "Hello!");
155 Notice that we have to return a `MonoString', and we use the
156 `mono_string_new' API call to obtain this from a string.
158 * Invoking Methods in the CIL universe
160 Calling a method in the CIL universe from C requires a number of steps:
163 * Obtaining the MonoMethod handle to the method.
165 * The method invocation.
168 ** Obtaining a MonoMethod
170 To get a MonoMethod there are several ways.
172 You can get a MonoClass (the structure representing a type)
177 mono_class_from_name (MonoImage *image, const char* name_space, const char *name);
180 and then loop in the returned class method array until you get
181 the one you're looking for. There are examples of such
182 searches as static functions in several C files in
183 metadata/*.c: we need to expose one through the API and remove
186 The other, simpler, way is to use the functions in
187 debug-helpers.h: there are examples of their use in monograph,
188 mint and the jit as well. You basically use a string
189 description of the method, like:
192 "System.Object:GetHashCode()"
195 and create a MonoMethodDesc out of it with:
198 MonoMethodDesc* mono_method_desc_new (const char *name, gboolean include_namespace);
204 MonoMethod* mono_method_desc_search_in_class (MonoMethodDesc *desc, MonoClass *klass);
205 MonoMethod* mono_method_desc_search_in_image (MonoMethodDesc *desc, MonoImage *image);
208 to search for the method in a class or in an image. You would
209 tipically do this just once at the start of the program and
210 store the result for reuse somewhere.
214 There are two functions to call a managed method:
218 mono_runtime_invoke (MonoMethod *method, void *obj, void **params,
222 mono_runtime_invoke_array (MonoMethod *method, void *obj, MonoArray *params,
226 obj is the 'this' pointer, it should be NULL for static
227 methods, a MonoObject* for object instances and a pointer to
228 the value type for value types.
230 The params array contains the arguments to the method with the
231 same convention: MonoObject* pointers for object instances and
232 pointers to the value type otherwise. The _invoke_array
233 variant takes a C# object[] as the params argument (MonoArray
234 *params): in this case the value types are boxed inside the
235 respective reference representation.
237 From unmanaged code you'll usually use the
238 mono_runtime_invoke() variant.
240 Note that this function doesn't handle virtual methods for
241 you, it will exec the exact method you pass: we still need to
242 expose a function to lookup the derived class implementation
243 of a virtual method (there are examples of this in the code,
246 You can pass NULL as the exc argument if you don't want to
247 catch exceptions, otherwise, *exc will be set to the exception
248 thrown, if any. if an exception is thrown, you can't use the
249 MonoObject* result from the function.
251 If the method returns a value type, it is boxed in an object
254 We have plans for providing an additional method that returns
255 an unmanaged->managed thunk like this:
258 void* mono_method_get_unmanaged_thunk (MonoMethod *method);
261 You'll be able to store the returned pointer in a function
262 pointer with the proper signature and call that directly from
266 typedef gint32 (*GetHashCode) (MonoObject *obj);
268 GetHashCode func = mono_method_get_unmanaged_thunk (System_Object_GetHashCode_method);
270 gint32 hashvalue = func (myobject);
273 It may not be possible to manage exceptions in that case,
274 though. I need to think more about it.
278 If your application creates threads on its own, and you want them to
279 be able to call code into the CIL universe with Mono, you have to
280 register the thread with Mono before issuing the call.
282 To do so, call the mono_thread_attach() function before you execute
283 any managed code from the thread
287 See the sample programs in mono/sample/embed for examples of
288 embedding the Mono runtime in your application.