.NET Framework Use SafeHandle when wrapping unmanaged resources


Example

When writing wrappers for unmanaged resources, you should subclass SafeHandle rather than trying to implement IDisposable and a finalizer yourself. Your SafeHandle subclass should be as small and simple as possible to minimize the chance of a handle leak. This likely means that your SafeHandle implementation would an internal implementation detail of a class which wraps it to provide a usable API. This class ensures that, even if a program leaks your SafeHandle instance, your unmanaged handle is released.

using System.Runtime.InteropServices;

class MyHandle : SafeHandle
{
    public override bool IsInvalid => handle == IntPtr.Zero;
    public MyHandle() : base(IntPtr.Zero, true)
    { }

    public MyHandle(int length) : this()
    {
        SetHandle(Marshal.AllocHGlobal(length));
    }

    protected override bool ReleaseHandle()
    {
        Marshal.FreeHGlobal(handle);
        return true;
    }
}

Disclaimer: This example is an attempt to show how to guard a managed resource with SafeHandle which implements IDisposable for you and configures finalizers appropriately. It is very contrived and likely pointless to allocate a chunk of memory in this manner.