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### Namespaces, Threads, and Go
On Linux each OS thread can have a different network namespace. Go's thread scheduling model switches goroutines between OS threads based on OS thread load and whether the goroutine would block other goroutines. This can result in a goroutine switching network namespaces without notice and lead to errors in your code.
### Namespace Switching
Switching namespaces with the `ns.Set()` method is not recommended without additional strategies to prevent unexpected namespace changes when your goroutines switch OS threads.
Go provides the `runtime.LockOSThread()` function to ensure a specific goroutine executes on its current OS thread and prevents any other goroutine from running in that thread until the locked one exits. Careful usage of `LockOSThread()` and goroutines can provide good control over which network namespace a given goroutine executes in.
For example, you cannot rely on the `ns.Set()` namespace being the current namespace after the `Set()` call unless you do two things. First, the goroutine calling `Set()` must have previously called `LockOSThread()`. Second, you must ensure `runtime.UnlockOSThread()` is not called somewhere in-between. You also cannot rely on the initial network namespace remaining the current network namespace if any other code in your program switches namespaces, unless you have already called `LockOSThread()` in that goroutine. Note that `LockOSThread()` prevents the Go scheduler from optimally scheduling goroutines for best performance, so `LockOSThread()` should only be used in small, isolated goroutines that release the lock quickly.
### Do() The Recommended Thing
The `ns.Do()` method provides control over network namespaces for you by implementing these strategies. All code dependent on a particular network namespace should be wrapped in the `ns.Do()` method to ensure the correct namespace is selected for the duration of your code. For example:
```go
targetNs, err := ns.NewNS()
if err != nil {
return err
}
err = targetNs.Do(func(hostNs ns.NetNS) error {
dummy := &netlink.Dummy{
LinkAttrs: netlink.LinkAttrs{
Name: "dummy0",
},
}
return netlink.LinkAdd(dummy)
})
```
### Further Reading
- https://github.com/golang/go/wiki/LockOSThread
- http://morsmachine.dk/go-scheduler
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