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Prevent race from prefetching (#4368)

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sschepens 2021-01-15 09:32:49 -03:00 • committed by GitHub
parent caaaf9ff3e
commit b2a22eff04
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1 changed files with 16 additions and 20 deletions
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36
plugin/cache/handler.go vendored
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@ -39,39 +39,28 @@ func (c *Cache) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg)
ttl = i.ttl(now)
}
if i == nil {
if !do {
setDo(rc)
}
crr := &ResponseWriter{ResponseWriter: w, Cache: c, state: state, server: server, do: do}
return plugin.NextOrFailure(c.Name(), c.Next, ctx, crr, rc)
return c.doRefresh(ctx, state, crr)
}
if ttl < 0 {
servedStale.WithLabelValues(server).Inc()
// Adjust the time to get a 0 TTL in the reply built from a stale item.
now = now.Add(time.Duration(ttl) * time.Second)
addr := w.LocalAddr() // See https://github.com/coredns/coredns/issues/4271, unclear how, but pull this out of the goroutine, and get the address here.
go func() {
if !do {
setDo(rc)
}
crr := &ResponseWriter{Cache: c, state: state, server: server, prefetch: true, remoteAddr: addr, do: do}
plugin.NextOrFailure(c.Name(), c.Next, ctx, crr, rc)
}()
cw := newPrefetchResponseWriter(server, state, c)
go c.doPrefetch(ctx, state, cw, i, now)
} else if c.shouldPrefetch(i, now) {
cw := newPrefetchResponseWriter(server, state, c)
go c.doPrefetch(ctx, state, cw, i, now)
}
resp := i.toMsg(r, now, do)
w.WriteMsg(resp)
if c.shouldPrefetch(i, now) {
go c.doPrefetch(ctx, state, server, i, now)
}
return dns.RcodeSuccess, nil
}
func (c *Cache) doPrefetch(ctx context.Context, state request.Request, server string, i *item, now time.Time) {
cw := newPrefetchResponseWriter(server, state, c)
cachePrefetches.WithLabelValues(server).Inc()
plugin.NextOrFailure(c.Name(), c.Next, ctx, cw, state.Req)
func (c *Cache) doPrefetch(ctx context.Context, state request.Request, cw *ResponseWriter, i *item, now time.Time) {
cachePrefetches.WithLabelValues(cw.server).Inc()
c.doRefresh(ctx, state, cw)
// When prefetching we loose the item i, and with it the frequency
// that we've gathered sofar. See we copy the frequencies info back
@ -81,6 +70,13 @@ func (c *Cache) doPrefetch(ctx context.Context, state request.Request, server st
}
}
func (c *Cache) doRefresh(ctx context.Context, state request.Request, cw *ResponseWriter) (int, error) {
if !state.Do() {
setDo(state.Req)
}
return plugin.NextOrFailure(c.Name(), c.Next, ctx, cw, state.Req)
}
func (c *Cache) shouldPrefetch(i *item, now time.Time) bool {
if c.prefetch <= 0 {
return false