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# writeTimestamp(counterHeap:index:)

Writes a GPU timestamp into the given counter heap.

```
func writeTimestamp(counterHeap: any MTL4CounterHeap, index: Int)
```

## Parameters

`counterHeap`

[`MTL4CounterHeap`](/documentation/Metal/MTL4CounterHeap) to write the timestamp into.

`index`

The index within the [`MTL4CounterHeap`](/documentation/Metal/MTL4CounterHeap) that Metal writes the timestamp to.

## Discussion

This method captures a timestamp after work prior to this command in the command buffer is complete.
Work after this call may or may not have started.

You are responsible for ensuring the `counterHeap` is of type [`MTL4CounterHeapType.timestamp`](/documentation/Metal/MTL4CounterHeapType/timestamp).

---

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