Question about httptrace synchronization

[Eli Lindsey]

Example code (note that it won’t actually execute in the playground since it’s making network calls):

https://play.golang.com/p/V9Z-ErjgICW

My assumption was that this code is a potential data race and requires additional synchronization on t. net/http/httptrace in particular says: "Functions may be called concurrently from different goroutines and some may be called after the request has completed or failed.”

However, I see code sans synchronization frequently in the wild, httpstat being one example (https://github.com/davecheney/httpstat/blob/master/main.go#L221).

Is there some additional synchronization guarantee provided by eg. client.Do() that I’m missing and that makes this safe, or is the fact that it doesn’t trip a race happenstance? 

-eli