P/Invoke to dynamically loaded library on Mono

Question

I\'m writing a cross-platform .NET library that uses some unmanaged code. In the static constructor of my class, the platform is detected and the appropriate unmanaged library

Answer 1

After much searching and head-scratching, I've discovered a solution. Full control can be exercised over the P/Invoke process by using dynamic P/Invoke to tell the runtime exactly where to find the code.

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Edit:

Windows solution

You need these imports:

[DllImport("kernel32.dll")]
protected static extern IntPtr LoadLibrary(string filename);

[DllImport("kernel32.dll")]
protected static extern IntPtr GetProcAddress(IntPtr hModule, string procname);

The unmanaged library should be loaded by calling LoadLibrary:

IntPtr moduleHandle = LoadLibrary("path/to/library.dll");

Get a pointer to a function in the dll by calling GetProcAddress:

IntPtr ptr = GetProcAddress(moduleHandle, methodName);

Cast this ptr to a delegate of type TDelegate:

TDelegate func = Marshal.GetDelegateForFunctionPointer(
    ptr, typeof(TDelegate)) as TDelegate;

Linux Solution

Use these imports:

[DllImport("libdl.so")]
protected static extern IntPtr dlopen(string filename, int flags);

[DllImport("libdl.so")]
protected static extern IntPtr dlsym(IntPtr handle, string symbol);

const int RTLD_NOW = 2; // for dlopen's flags 

Load the library:

IntPtr moduleHandle = dlopen(modulePath, RTLD_NOW);

Get the function pointer:

IntPtr ptr = dlsym(moduleHandle, methodName);

Cast it to a delegate as before:

TDelegate func = Marshal.GetDelegateForFunctionPointer(
    ptr, typeof(TDelegate)) as TDelegate;

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For a helper library that I wrote, see my GitHub.