main/syscalls/sampler_start.md

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# zx_sampler_start

## Summary

Begin sampling to the provided IOBuffer.

## Declaration

```c
#include <zircon/syscalls.h>

zx_status_t zx_sampler_start(zx_handle_t iobuffer);
```

## Description

Begin sampling each attached thread and writing each sample to the
provided IOBuffer. The provided IOBuffer must be one previously returned
by zx_sampler_create.

Attempting to start a session which has already been started will return
an error, but will not stop or otherwise modify the session.

Restarting a previously started/stopped session will continue writing to
the buffers where the previous session left off.

## Errors

`ZX_ERR_NOT_SUPPORTED`  `kernel.enable-debugging-syscalls` is not set to `true`
on the kernel command line or the experimental_thread_sampler_enabled
build param is not set to true.

`ZX_ERR_PERMISION_DENIED` *iobuffer* is not an IOBuffer returned by zx_sampler_create.

`ZX_ERR_BAD_STATE` the sampler has already been started.

## See also

 - [`zx_sampler_create()`]
 - [`zx_sampler_stop()`]

[`zx_sampler_create()`]: sampler_create.md
[`zx_sampler_stop()`]: sampler_stop.md