IDisposable pattern, is SafeFileHandle an unmanaged resource?

Question

Take the following snippet of IDisposable pattern generated by Resharper:

[NotNull]
private SafeFileHandle Handle { get; }

#region IDisposable

private bool IsDisposed { get; set; }

public void Dispose()
{
    Dispose(true);
    GC.SuppressFinalize(this);
}

private void ReleaseUnmanagedResources()
{
    // TODO release unmanaged resources here
}

private void Dispose(bool disposing)
{
    if (IsDisposed)
        return;

    ReleaseUnmanagedResources();

    if (disposing)
        Handle.Dispose();

    IsDisposed = true;
}

~Whatever()
{
    Dispose(false);
}

Resharper considers SafeFileHandle as a managed resource, but this handle is about an unmanaged resource (CreateFile).

Question:

Should a SafeFileHandle be considered a managed or unmanaged resource when disposing it?

Answer 1

All C# classes and structs are managed resources¹.

Unmanaged resources are typically pointed to by an IntPtr, or something similar. You normally need to do something very deliberate to get your hands on one (such as P/Invoking some native method, or using one of the methods on Marshal).

SafeFileHandle is a subclass of SafeHandle, which is a type specifically made to wrap unmanaged resources. SafeHandle defines its own finalizer, which releases the unmanaged resource in a suitable way if necessary.

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It's good advice to never own your own unmanaged resources, and instead always use a SafeHandle / CriticalFinalizerObject subclass to manage them.

This avoids one of the big P/Invoke pitfalls, and also means you don't have to implement the full IDisposable pattern in your code: you only need to define a Dispose() method which calls Dispose() on your SafeHandles, and don't need to implement a finalizer.

(Some people may need to deviate from this for performance reasons, but those people are few and far between)

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¹Generic types with an unmanaged constraint aside...