---
title: "sampleCounters(sampleBuffer:sampleIndex:barrier:)"
framework: metal
role: symbol
role_heading: Instance Method
path: "metal/mtlaccelerationstructurecommandencoder/samplecounters(samplebuffer:sampleindex:barrier:)"
---

# sampleCounters(sampleBuffer:sampleIndex:barrier:)

Encodes a command to sample hardware counters at this point in the acceleration structure pass and store the samples into a counter sample buffer.

## Declaration

```swift
func sampleCounters(sampleBuffer: any MTLCounterSampleBuffer, sampleIndex: Int, barrier: Bool)
```

## Parameters

- `sampleBuffer`: The sample buffer to sample into.
- `sampleIndex`: The index in the counter buffer to write the sample.
- `barrier`: A Boolean value that states whether to insert a barrier before taking the sample.

## Mentioned in

Sampling GPU data into counter sample buffers

## Discussion

Discussion Inserting a barrier ensures that any work you encoded 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 encoded by this encoder. Using a barrier leads to more repeatable counter results but can negatively impact performance. Regardless of whether you set a barrier, the GPU doesn’t isolate the sampling from work encoded by other encoders.