[Mono-list] NullReferenceException when calling thunk

[Robert Jordan]

Hi Tom,

On 23.01.2013 18:16, tomason wrote:
> That's interesting that the thunks are a seldom-used feature.  The
> documentation says that they're more efficient AND they're way easier to
> use than mono_runtime_invoke.  Is the latter really more popular or is
> there a 3rd way that I don't know about yet?

The 3rd way revolves around calling back a delegate registered
from the managed world via p/invoke:

// C#

delegate float AddMethod(float a, float b);

class Test
{
	[DllImport(...)]
	public static extern
	void RegisterAddCallback(AddMethod floatDelegate);
}

// C/C++

typedef float (*AddMethod)(float, float);
AddMethod managedAddMethod;

void
RegisterAddCallback(AddMethod delegate)
{
	managedAddMethod = delegate;
}

static
float Add(float a, float b)
{
	assert(managedAddMethod);
	return managedAddMethod(a, b);
}


Since this approach is requiring quite a bit of bookkeeping,
it only makes sense to use it for a few methods (or at large scale
using some kind of code generation).

Robert


>
> Thanks!
> -Tom
>
>
> On Wed, Jan 23, 2013 at 2:57 AM, Robert Jordan [via Mono] <
> ml-node+s1490590n4658237h75 at n4.nabble.com> wrote:
>
>> Hi,
>>
>> On 23.01.2013 06:43, tomason wrote:
>>> Where MonoAddFunc is defined like this:
>>> typedef float (*MonoAddFunc)(MonoObject*, float, float);
>>
>> You you're testing under Windows, the typedef must be stdcall:
>>
>> typedef float (__stdcall *MonoAddFunc)(MonoObject*, float, float);
>>
>>
>> A note on thunks: this is a seldom used feature, so odds are
>> that the code got a little bitrotten. Please file a bug if
>> you can rule out the stdcall issue, and I'll take a look
>> at it.
>>
>> Robert
>>
>>
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