# sampleCounters(sampleBuffer:sampleIndex:barrier:) Encodes a command that samples the GPU’s hardware counters during a blit pass and stores the data in a counter sample buffer. ``` func sampleCounters(sampleBuffer: any MTLCounterSampleBuffer, sampleIndex: Int, barrier: Bool) ``` ## Parameters `sampleBuffer` A counter sample buffer where the command stores the sample data. `sampleIndex` A location within `sampleBuffer` where the command stores the sample data. `barrier` A Boolean value that indicates whether the command inserts a barrier before taking the sample. ## Discussion Inserting a barrier ensures that any work you encode with this encoder is complete before the GPU samples the hardware counters. If you don’t insert a barrier, the GPU can sample the counters concurrently with other commands you encode with this encoder. Using a barrier can help the counter results be more predictable and repeatable, but it may adversely affect your app’s runtime performance. > Note: > The GPU doesn’t isolate this sampling command from any commands that come from another encoder, with or without a barrier. --- 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)