# Concurrency | Sentry for Zap

Concurrent Go programs use goroutines, a form of lightweight thread managed by the Go runtime. Because goroutines run concurrently, every goroutine has to keep track of its own Sentry-related data locally. Otherwise, data races can introduce subtle bugs to your programs, and the consequences vary from nothing apparent to unexpected crashes or, worse, accidentally mixing up data stored in the `Scope`. More on this in the [Scopes and Hubs](https://docs.sentry.io/platforms/go/guides/zap/enriching-events/scopes.md) section.

The easiest way to handle this, is to create a new `Hub` for every goroutine you start, however this would require you to rebind the current `Client` and handle `Scope` yourself. That is why we provide a helper method called `Clone`. It takes care of creating a `Hub`, cloning existing `Scope` and reassigning it alongside `Client` to newly create instance.

Once cloned, `Hub` is completely isolated and can be used safely inside concurrent call. However, instead of using globally exposed methods, they should be called directly on the `Hub`.

Here are two examples:

* a recommended deterministic call on `Hub` that is safe

```go
// Example of __CORRECT__ use of scopes inside a Goroutine

go func(localHub *sentry.Hub) {
	// as goroutine argument
	localHub.ConfigureScope(func(scope *sentry.Scope) {
		scope.SetTag("secretTag", "go#1")
	})
	localHub.CaptureMessage("Hello from Goroutine! #1")
}(sentry.CurrentHub().Clone())

go func() {
	// or created locally
	localHub := sentry.CurrentHub().Clone()
	localHub.ConfigureScope(func(scope *sentry.Scope) {
		scope.SetTag("secretTag", "go#2")
	})
	localHub.CaptureMessage("Hello from Goroutine! #2")
}()
```

* a discouraged non-deterministic call on `Hub` that would leak information between threads

```go
// Example of __INCORRECT__ use of scopes inside a Goroutine - DON'T USE IT!

go func() {
	sentry.ConfigureScope(func(scope *sentry.Scope) {
		scope.SetTag("secretTag", "go#1")
	})
	sentry.CaptureMessage("Hello from Goroutine! #1")
}()

go func() {
	sentry.ConfigureScope(func(scope *sentry.Scope) {
		scope.SetTag("secretTag", "go#2")
	})
	sentry.CaptureMessage("Hello from Goroutine! #2")
}()

// at this point both events can have either `go#1` tag or `go#2` tag. We'll never know.
```
