How to wrap native array?

mid 5741

This is a native struct:

struct BufferInfo
{
void* buffers[2];
}

that gets passed to this native function:

bool CreateBuffers( BufferInfo* buffersInfo );

On return from this function the buffers member of buffersInfo points to the two halves of a double buffer, the size of which is known. I'm trying to wrap the native code with C++/CLI. I cannot use array<Byte,2>^ to wrap void* buffers[2] because array<> is only for allocations in the CLR heap. Is there a way to wrap the native array and treat it like a managed one? Copying or marshaling the data in the buffers is not an option for performance reasons.

Luc Pattyn

Hi, in my experience it is best to allocate a managed array, get it pinned down so the GC does not move it, fetch its pointer (IntPtr), then pass it on to the native world; that way nothing needs being copied or marshaled. I typically use an object of this class to support this process (it happens to be C# code); the C# using statement makes sure it gets disposed of as soon as appropriate:

/// /// An LP_Pinner object pins an object for as long as the LP_Pinner
/// object is alive.
///
/// /// This is the preferred use when the pointer value is not needed:
/// using (new LP_Pinner(objectThatNeedsPinning)) {
/// .. use the object here, it is pinned now ...
/// }
/// This is the preferred use when the pointer value is needed:
/// using (LP_Pinner pinning=new LP_Pinner(objectThatNeedsPinning)) {
/// IntPtr ptr=pinning.Ptr;
/// .. use the object here, it is pinned now ...
/// }
///
public class LP_Pinner : IDisposable {
private static ILP_Environment env=LP_Environment.GetEnvironment();
private GCHandle handle;
private bool disposed;
private IntPtr ptr;

/// /// Creates an instance op LP\_Pinner, and pins the argument.
/// 
/// 
public LP\_Pinner(object obj) {
	//env.log(0,"AllocPinned "+obj.GetType().Name);
	handle=GCHandle.Alloc(obj, GCHandleType.Pinned);
	ptr=handle.AddrOfPinnedObject();
}

/// /// Undoes the pinning.
/// 
~LP\_Pinner() {
	Dispose();
}

/// /// Disposes of the object's internal resources.
/// 
public void Dispose() {
	if (!disposed) {
		//env.log(0,"Free");
		disposed=true;
		handle.Free();
		ptr=IntPtr.Zero;
	}
}

/// /// Returns the pointer to the pinned object.
/// 
public IntPtr Ptr {get {return ptr;}}

}

Hope this helps. :)

Luc Pattyn

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mid 5741

Unfortunately that is not an option. I have no control over the native code, which is an interface to an audio hardware driver that manages its own buffers.

Luc Pattyn

I see no way you can have an unmanaged array being promoted to a managed one without copying it all. You can of course pass the pointer value from native to managed world, and use it there as a pointer, using unsafe code (or whatever it is called in C++/CLI) and pointer operations. But then it is not a managed object at all. :)

Luc Pattyn

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mid 5741

OK. Thanks for your input. I'm going to see if a managed class with a private void* member can use an indexed property to give access to the bytes in the buffer and not affect performance.