# Synchronizing events across multiple devices or processes Use shareable events to synchronize your app’s work across multiple devices or processes. ## Discussion The following figure and code show a shareable event that synchronizes graphics rendering on one device with compute processing on another.  ```objective-c - (void)setupMultipleDeviceEvent { // Shareable event _sharedEvent = [_deviceA newSharedEvent]; // Built-in GPU command queue _commandQueueA = [_deviceA newCommandQueue]; // External GPU command queue _commandQueueB = [_deviceB newCommandQueue]; } - (void)renderFrame { // Device A (Graphics Rendering) id commandBufferA = [_commandQueueA commandBuffer]; /* Encode first render pass */ [commandBufferA encodeSignalEvent:_sharedEvent value:1]; /* Encode second render pass */ [commandBufferA encodeWaitForEvent:_sharedEvent value:2]; /* Encode third render pass */ [commandBufferA commit]; // Device B (Compute Processing) id commandBufferB = [_commandQueueB commandBuffer]; /* Encode first compute pass */ [commandBufferB encodeWaitForEvent:_sharedEvent value:1]; /* Encode second compute pass */ [commandBufferB encodeSignalEvent:_sharedEvent value:2]; /* Encode third compute pass */ [commandBufferB commit]; } ``` During setup, the code creates a shareable event ([`MTLSharedEvent`](/documentation/Metal/MTLSharedEvent)) and command queues on two different devices. Like the example shown in [Synchronizing events within a single device](/documentation/Metal/synchronizing-events-within-a-single-device), it encodes render commands onto the first queue and compute commands on the second queue. You call the same methods when signaling and waiting on shared events as you do when working with events on a single device. The only difference is that the queues are associated with different devices and the event being used to synchronize access is a shared event. The code shown above assumes you’ve created each resource on both device objects, and each pair of resources share a single allocation of memory. This strategy means that change made by one device object are visible to the other device object. For an example of how to do this, see [Selecting device objects for compute processing](/documentation/Metal/selecting-device-objects-for-compute-processing). --- 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)