# MTLCopyAllDevicesWithObserver(handler:) Returns an array of all the Metal GPU devices in the system and registers a notification handler that Metal calls when the device list changes. ``` func MTLCopyAllDevicesWithObserver(handler: @escaping (any MTLDevice, MTLDeviceNotificationName) -> Void) -> (devices: [any MTLDevice], observer: NSObject) ``` ## Parameters `handler` A notification handler you implement that Metal calls when the system adds or removes a GPU device from the system. ## Return Value - `devices`: An array of [`MTLDevice`](/documentation/Metal/MTLDevice) instances - `observer`: An object instance that represents an observer the function creates for you. ## Discussion Keep a copy of `observer` in your app in case you want to stop receiving notifications. You can stop receiving notifications by passing `observer` to the [`MTLRemoveDeviceObserver(_:)`](/documentation/Metal/MTLRemoveDeviceObserver(_:)) function. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)