[Mono-list] [embedding] "moving from mono_runtime_invoke() to mono_method_get_unmanaged_thunk()" or "how to call class method that takes and returns a string via thunks"

[Julian Mayer]

i didn't list any specific crash, because i tried in a million different ways and got a different crash each time.

i've solved this now. it seems, a unmanaged thunk takes a hidden additional parameter, MonoException ** which can't be NULL. of course this isn't documented anywhere.

for reference, i got the mentioned call working using:

    typedef MonoObject* (*ParseToJSON) (MonoString *obj1,MonoException **obj2);
    ParseToJSON func = mono_method_get_unmanaged_thunk(method);
    MonoString *s1 = mono_string_new (domain, "A-B");
    MonoException *exc = NULL;
    MonoObject *result = func(s1,&exc);
    MonoString *resultstring = mono_object_to_string(result, NULL);
    char *resultCString = mono_string_to_utf8(resultstring);


> On 11.11.2015, at 21:34, Rodrigo Kumpera <kumpera at gmail.com> wrote:
> 
> How does it crash? Did you try debugging it?
> 
> The invocation looks ok.
> 
> On Wed, Nov 11, 2015 at 3:03 PM, Core_Code <julian at corecode.at> wrote:
> hello,
> 
> we are currently embedding Mono to use a C# DLL, which works fine.
> 
> we are using mono_runtime_invoke() to invoke a class method and are
> obtaining the resulting object just fine.
> 
> however, for performance reasons we'd like to switch to using the 'unmanaged
> thunks', which we did not get to work. our call differes from the example in
> the 'embedding mono' docs by the parameters and the fact that we are calling
> a class method. however we try, just different crashes.
> 
> 
> the function we have to call has this prototype:
> public static string ParseToJSON(string input)
> 
> which seems to translate to a mono method description of
> XLParser.ExcelFormulaParser:ParseToJSON (string)
> 
> we have no problem using mono_runtime_invoke() to call it exactly like this:
> 
> 
> MonoAssembly *assembly = mono_domain_assembly_open(domain,
> "/path/to/XLParser.dll");
> MonoImage *image = mono_assembly_get_image(assembly);
> MonoClass *classHandle = mono_class_from_name(image, "XLParser",
> "ExcelFormulaParser");
> const char *descAsString = "XLParser.ExcelFormulaParser:ParseToJSON
> (string)";
> MonoMethodDesc *description = mono_method_desc_new(descAsString, 0);
> method = mono_method_desc_search_in_class(description, classHandle);
> void *args[1] = {mono_string_new (domain, "A+B")};
> MonoObject *resultObject = mono_runtime_invoke(method, NULL, args, NULL);
> MonoString *resultString = mono_object_to_string(resultObject, NULL);
> char *resultCString = mono_string_to_utf8(resultString);
> 
> 
> now we are trying the thunk method:
> 
> typedef MonoObject* (*ParseToJSON) (MonoString *obj1,MonoString *obj2);
> ParseToJSON func = mono_method_get_unmanaged_thunk(method);
> MonoString *s = mono_string_new (domain, "A+B");
> MonoObject *result = func(s,NULL);
> MonoString *resultstring = mono_object_to_string(result, NULL);
> char *str = mono_string_to_utf8(resultstring);
> 
> but it crashes - any idea how to call a class method via thunks?
> 
> 
> 
> 
> --
> View this message in context: http://mono.1490590.n4.nabble.com/embedding-moving-from-mono-runtime-invoke-to-mono-method-get-unmanaged-thunk-or-how-to-call-class-me-tp4666935.html
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