2 Embedding the Mono runtime, preliminary version
4 Miguel de Icaza, Paolo Molaro.
6 This document describes how to embed the Mono runtime in your
7 application, and how to invoke CIL methods from C, and how to
8 invoke C code from CIL.
10 * Embedding the runtime.
12 Embedding the runtime consists of various steps:
14 * Compiling and linking the Mono runtime
16 * Initializing the Mono runtime
18 * Optionally expose C code to the C#/CIL universe.
20 These are discussed in detail next.
22 ** Compiling and Linking
24 To embed the runtime, you have to link your code against the
25 Mono runtime libraries. To do this, you want to pass the
26 flags returned by pkg-config to your compiler:
28 pkg-config --cflags --libs mono
32 gcc sample.c `pkg-config --cflags --libs mono`
34 You can separate the compilation flags from the linking flags, for
35 instance, you can use the following macros in your makefile:
37 CFLAGS=`pkg-config --cflags mono`
38 LDFLAGS=`pkg-config --libs mono`
40 ** Initializing the Mono runtime
42 To initialize the runtime, call mono_jit_init, like this:
46 domain = mono_jit_init ("domain-name");
48 That will return a MonoDomain where your code will be
49 executed. You can create multiple domains. Each domain is
50 isolated from the other domains and code in one domain will
51 not interfere with code in other domains. This is useful if
52 you want to host different applications in your program.
54 Then you can load an assembly containing code into the domain:
56 MonoAssembly *assembly;
58 assembly = mono_domain_assembly_open (domain, "file.dll");
62 In the above example, the contents of `file.dll' will be
63 loaded into the domain. This only loads the code, but it will
64 not execute anything yet. You can replace `file.dll' with
65 another transport file, like `file.exe'
67 To start executing code, you must invoke a method in the
68 assembly, or if you have provided a static Main method (an
69 entry point), you can use the convenience function:
71 retval = mono_jit_exec (domain, assembly, argc - 1, argv + 1);
73 If you want to invoke a different method, look at the
74 `Invoking Methods in the CIL universe' section later on.
76 ** Shutting down the runtime
78 To shutdown the Mono runtime, you have to clean up all the
79 domains that were created, use this function:
81 mono_jit_cleanup (domain);
83 ** Applications that use threads.
85 The Boehm GC system needs to catch your calls to the pthreads
86 layer, so in each file where you use pthread.h you should
87 include the <gc/gc.h> file.
89 * Exposing C code to the CIL universe
91 The Mono runtime provides two mechanisms to expose C code to
92 the CIL universe: internal calls and native C code. Internal
93 calls are tightly integrated with the runtime, and have the
94 least overhead, as they use the same data types that the
97 The other option is to use the Platform Invoke (P/Invoke) to
98 call C code from the CIL universe, using the standard P/Invoke
101 To register an internal call, use this call in the C code:
103 mono_add_internal_call ("Hello::Sample", sample);
105 Now, you need to declare this on the C# side:
108 using System.Runtime.CompilerServices;
111 [MethodImplAttribute(MethodImplOptions.InternalCall)]
112 extern static string Sample ();
115 Since this routine returns a string, here is the C definition:
120 return mono_string_new (mono_domain_get (), "Hello!");
123 Notice that we have to return a `MonoString', and we use the
124 `mono_string_new' API call to obtain this from a string.
126 * Invoking Methods in the CIL universe
128 Calling a method in the CIL universe from C requires a number of steps:
130 * Obtaining the MonoMethod handle to the method.
132 * The method invocation.
134 ** Obtaining a MonoMethod
136 To get a MonoMethod there are several ways.
138 You can get a MonoClass (the structure representing a type)
142 mono_class_from_name (MonoImage *image, const char* name_space, const char *name);
144 and then loop in the returned class method array until you get
145 the one you're looking for. There are examples of such
146 searches as static functions in several C files in
147 metadata/*.c: we need to expose one through the API and remove
150 The other, simpler, way is to use the functions in
151 debug-helpers.h: there are examples of their use in monograph,
152 mint and the jit as well. You basically use a string
153 description of the method, like:
155 "System.Object:GetHashCode()"
157 and create a MonoMethodDesc out of it with:
159 MonoMethodDesc* mono_method_desc_new (const char *name, gboolean include_namespace);
163 MonoMethod* mono_method_desc_search_in_class (MonoMethodDesc *desc, MonoClass *klass);
164 MonoMethod* mono_method_desc_search_in_image (MonoMethodDesc *desc, MonoImage *image);
166 to search for the method in a class or in an image. You would
167 tipically do this just once at the start of the program and
168 store the result for reuse somewhere.
172 There are two functions to call a managed method:
175 mono_runtime_invoke (MonoMethod *method, void *obj, void **params,
179 mono_runtime_invoke_array (MonoMethod *method, void *obj, MonoArray *params,
182 obj is the 'this' pointer, it should be NULL for static
183 methods, a MonoObject* for object instances and a pointer to
184 the value type for value types.
186 The params array contains the arguments to the method with the
187 same convention: MonoObject* pointers for object instances and
188 pointers to the value type otherwise. The _invoke_array
189 variant takes a C# object[] as the params argument (MonoArray
190 *params): in this case the value types are boxed inside the
191 respective reference representation.
193 From unmanaged code you'll usually use the
194 mono_runtime_invoke() variant.
196 Note that this function doesn't handle virtual methods for
197 you, it will exec the exact method you pass: we still need to
198 expose a function to lookup the derived class implementation
199 of a virtual method (there are examples of this in the code,
202 You can pass NULL as the exc argument if you don't want to
203 catch exceptions, otherwise, *exc will be set to the exception
204 thrown, if any. if an exception is thrown, you can't use the
205 MonoObject* result from the function.
207 If the method returns a value type, it is boxed in an object
210 We have plans for providing an additional method that returns
211 an unmanaged->managed thunk like this:
213 void* mono_method_get_unmanaged_thunk (MonoMethod *method);
215 You'll be able to store the returned pointer in a function
216 pointer with the proper signature and call that directly from
219 typedef gint32 (*GetHashCode) (MonoObject *obj);
221 GetHashCode func = mono_method_get_unmanaged_thunk (System_Object_GetHashCode_method);
223 gint32 hashvalue = func (myobject);
225 It may not be possible to manage exceptions in that case,
226 though. I need to think more about it.
230 If your application creates threads on its own, and you want them to
231 be able to call code into the CIL universe with Mono, you have to
232 register the thread with Mono before issuing the call.
234 To do so, call the mono_thread_attach() function before you execute
235 any managed code from the thread
239 See the sample programs inmono/sample/embed for examples of
240 embedding the Mono runtime in your application.