Backport of cache: prevent goroutine leak in agent cache into release/1.12.x#15017
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Backport
This PR is auto-generated from #14908 to be assessed for backporting due to the inclusion of the label backport/1.12.
The below text is copied from the body of the original PR.
Description
There is a bug in the error handling code for the Agent cache subsystem discovered by @boxofrad :
NotifyCallbackcallsnotifyBlockingQuerywhich callsgetWithIndexin a loop (which backs off on-error up to 1 minute)getWithIndexcallsfetchif there’s no valid entry in the cachefetchstarts a goroutine which callsFetchon the cache-type, waits for a while (again with backoff up to 1 minute for errors) and then callsfetchto trigger a refreshThe end result being that every 1 minute
notifyBlockingQueryspawns an ancestry of goroutines that essentially lives forever.This PR ensures that the goroutine started by
fetchcancels 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.
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