I’m trying to understand different garbage collection handle types in .NET memory management. Here’s what I know so far:
Handle Categories
Weak Handles - Don’t stop objects from being collected (like WeakReference)
Strong Handles - Prevent garbage collection of referenced objects
RefCounted Handles - Used internally for COM interop scenarios
Pinned Handles - This is where I need help
My Main Question
What’s the real purpose behind pinned GC handles? I understand they stop memory movement, but is there more to it?
Specific Issue
I have a jagged array CellData[][] bound to a WPF DataGrid. When I close the window, I see pinned handles pointing to empty CellData arrays through object[] references in memory analysis tools. I set the grid’s ItemsSource to null before closing.
Why does this pinning happen when I’m not using unsafe code? What component creates these pinned handles and for what reason?
Pinned handles are crucial for memory safety when you’re crossing between managed and unmanaged code. They don’t just stop the GC from moving things around - they guarantee your memory stays put during interop calls. Your DataGrid problem comes from how WPF works internally. The framework pins array elements when it converts managed collections to native structures for the rendering thread. These handles stick around because WPF keeps object pools and caches for better performance. The virtualization system holds onto references from previously rendered items even after you change ItemsSource. I’ve seen this same thing happen with complex data structures in enterprise apps. The pinned handles typically clear after the next major GC cycle, but WPF’s dependency property system can slow this down. Try implementing IDisposable on your data objects and call GC.WaitForPendingFinalizers after cleanup to speed things up.
yeah, pinned handles are there to keep objects from being moved by the GC, which is super impt in WPF since it talks to native code. your datagrid probs has threads or animations still using those spots. try fully disposing the datagrid instead of just nulling ItemsSource.
Those pinned handles are part of WPF’s performance optimization. The binding engine creates temporary pinned references when marshaling your array data to the native rendering pipeline. These handles keep your managed arrays in place while DirectX draws the cells.
The timing’s the real problem. Even after you null out ItemsSource, the visual system still has pending operations referencing your data. WPF batches work for performance.
I hit this same issue with a dashboard full of grids. Manual cleanup was a nightmare - you never know what’s still holding references internally.
What fixed it for me was automating the entire cleanup process. I built a workflow that disposes UI elements in the right order, forces layout updates, and handles timing issues automatically. No more memory leaks or leftover pinned handles.
The automation catches edge cases you’d miss manually - like waiting for animation timers to finish or making sure virtualized containers release their references.
You could set up something similar to handle your grid cleanup automatically instead of wrestling with WPF internals by hand.
Pinned handles lock objects at specific memory addresses so the garbage collector can’t move them around during compaction. This is crucial when managed memory talks to unmanaged code or native APIs. For your WPF DataGrid issue - WPF creates these pinned handles internally for data binding. The virtualization engine and rendering system need stable memory addresses when they’re working with DirectX or other native components. Even though you’re not using unsafe code directly, WPF does tons of unmanaged stuff behind the scenes. Those handles sticking around after you null out ItemsSource? That’s probably delayed cleanup or leftover references in the visual tree. Try calling UpdateLayout() or force a garbage collection to see if that clears them. WPF’s binding system is complex and sometimes holds references way longer than you’d expect.
Pinned handles do more than just prevent memory movement - they bridge managed and unmanaged memory. When .NET needs to pass managed object references to native code, it guarantees those objects won’t move during the call. In your WPF scenario, DataGrid’s virtualization probably creates pinned handles when marshaling array data to DirectX for rendering. WPF relies heavily on native components for visuals, so your jagged arrays get temporarily pinned during these interactions. What you’re seeing in memory tools are likely leftovers from UI virtualization that hasn’t finished cleanup yet. The binding engine also uses pinned handles to provide stable pointers during property change notifications. Since garbage collection runs on a separate thread, there’s usually a delay between nulling ItemsSource and actual cleanup happening. That’s why those handles stick around even after you think you’ve cleared the references.