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cmd/derper: optimize handleBootstrapDNS

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Do json formatting once, rather than on every request.

Use an atomic.Value.

name                   old time/op    new time/op    delta
HandleBootstrapDNS-10    6.35µs ± 0%    0.10µs ± 4%  -98.35%  (p=0.000 n=14+15)

name                   old alloc/op   new alloc/op   delta
HandleBootstrapDNS-10    3.20kB ± 0%    0.42kB ± 0%  -86.99%  (p=0.000 n=12+15)

name                   old allocs/op  new allocs/op  delta
HandleBootstrapDNS-10      41.0 ± 0%       3.0 ± 0%  -92.68%  (p=0.000 n=15+15)

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
This commit is contained in:
Josh Bleecher Snyder 2022-02-11 12:30:36 -08:00 committed by Josh Bleecher Snyder
parent e206a3663f
commit b9c92b90db
1 changed files with 11 additions and 17 deletions
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28
cmd/derper/bootstrap_dns.go
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@ -12,14 +12,11 @@
"net"
"net/http"
"strings"
"sync"
"sync/atomic"
"time"
)
var (
dnsMu sync.Mutex
dnsCache = map[string][]net.IP{}
)
var dnsCache atomic.Value // of []byte
var bootstrapDNSRequests = expvar.NewInt("counter_bootstrap_dns_requests")
@ -37,6 +34,7 @@ func refreshBootstrapDNS() {
if *bootstrapDNS == "" {
return
}
dnsEntries := make(map[string][]net.IP)
ctx, cancel := context.WithTimeout(context.Background(), time.Minute)
defer cancel()
names := strings.Split(*bootstrapDNS, ",")
@ -47,23 +45,19 @@ func refreshBootstrapDNS() {
log.Printf("bootstrap DNS lookup %q: %v", name, err)
continue
}
dnsMu.Lock()
dnsCache[name] = addrs
dnsMu.Unlock()
dnsEntries[name] = addrs
}
j, err := json.MarshalIndent(dnsCache, "", "\t")
if err != nil {
// leave the old values in place
return
}
dnsCache.Store(j)
}
func handleBootstrapDNS(w http.ResponseWriter, r *http.Request) {
bootstrapDNSRequests.Add(1)
dnsMu.Lock()
j, err := json.MarshalIndent(dnsCache, "", "\t")
dnsMu.Unlock()
if err != nil {
log.Printf("bootstrap DNS JSON: %v", err)
http.Error(w, "JSON marshal error", 500)
return
}
w.Header().Set("Content-Type", "application/json")
j, _ := dnsCache.Load().([]byte)
w.Write(j)
}