consul/.changelog/14908.txt

```release-note:bug
cache: prevent goroutine leak in agent cache
```
cache: prevent goroutine leak in agent cache (#14908) There is a bug in the error handling code for the Agent cache subsystem discovered: 1. NotifyCallback calls notifyBlockingQuery which calls getWithIndex in a loop (which backs off on-error up to 1 minute) 2. getWithIndex calls fetch if there’s no valid entry in the cache 3. fetch starts a goroutine which calls Fetch on the cache-type, waits for a while (again with backoff up to 1 minute for errors) and then calls fetch to trigger a refresh The end result being that every 1 minute notifyBlockingQuery spawns an ancestry of goroutines that essentially lives forever. This PR ensures that the goroutine started by `fetch` cancels any prior goroutine spawned by the same line for the same key. In isolated testing where a cache type was tweaked to indefinitely error, this patch prevented goroutine counts from skyrocketing. 2022-10-17 19:38:10 +00:00			```release-note:bug
			`cache: prevent goroutine leak in agent cache`
			```