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xTransport: avoid updating the host->IP map in multiple goroutines

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When a goroutine is updating an IP, keep serving the previous IP
to other goroutines.
This commit is contained in:
Frank Denis 2025-02-21 18:07:41 +01:00
parent 8264b43199
commit f49196c6e8
1 changed files with 28 additions and 9 deletions
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37
dnscrypt-proxy/xtransport.go
View file

@ -40,8 +40,9 @@ const (
)
type CachedIPItem struct {
ip net.IP
expiration *time.Time
ip net.IP
expiration *time.Time
updating_until *time.Time
}
type CachedIPs struct {
@ -105,7 +106,7 @@ func ParseIP(ipStr string) net.IP {
// If ttl < 0, never expire
// Otherwise, ttl is set to max(ttl, MinResolverIPTTL)
func (xTransport *XTransport) saveCachedIP(host string, ip net.IP, ttl time.Duration) {
item := &CachedIPItem{ip: ip, expiration: nil}
item := &CachedIPItem{ip: ip, expiration: nil, updating_until: nil}
if ttl >= 0 {
if ttl < MinResolverIPTTL {
ttl = MinResolverIPTTL
@ -118,8 +119,21 @@ func (xTransport *XTransport) saveCachedIP(host string, ip net.IP, ttl time.Dura
xTransport.cachedIPs.Unlock()
}
func (xTransport *XTransport) loadCachedIP(host string) (ip net.IP, expired bool) {
ip, expired = nil, false
// Mark an entry as being updated
func (xTransport *XTransport) markUpdatingCachedIP(host string) {
xTransport.cachedIPs.Lock()
item, ok := xTransport.cachedIPs.cache[host]
if ok {
now := time.Now()
until := now.Add(xTransport.timeout)
item.updating_until = &until
xTransport.cachedIPs.cache[host] = item
}
xTransport.cachedIPs.Unlock()
}
func (xTransport *XTransport) loadCachedIP(host string) (ip net.IP, expired bool, updating bool) {
ip, expired, updating = nil, false, false
xTransport.cachedIPs.RLock()
item, ok := xTransport.cachedIPs.cache[host]
xTransport.cachedIPs.RUnlock()
@ -130,6 +144,9 @@ func (xTransport *XTransport) loadCachedIP(host string) (ip net.IP, expired bool
expiration := item.expiration
if expiration != nil && time.Until(*expiration) < 0 {
expired = true
if item.updating_until != nil && time.Until(*item.updating_until) > 0 {
updating = true
}
}
return
}
@ -153,7 +170,7 @@ func (xTransport *XTransport) rebuildTransport() {
ipOnly := host
// resolveAndUpdateCache() is always called in `Fetch()` before the `Dial()`
// method is used, so that a cached entry must be present at this point.
cachedIP, _ := xTransport.loadCachedIP(host)
cachedIP, _, _ := xTransport.loadCachedIP(host)
if cachedIP != nil {
if ipv4 := cachedIP.To4(); ipv4 != nil {
ipOnly = ipv4.String()
@ -263,7 +280,7 @@ func (xTransport *XTransport) rebuildTransport() {
dlog.Debugf("Dialing for H3: [%v]", addrStr)
host, port := ExtractHostAndPort(addrStr, stamps.DefaultPort)
ipOnly := host
cachedIP, _ := xTransport.loadCachedIP(host)
cachedIP, _, _ := xTransport.loadCachedIP(host)
network := "udp4"
if cachedIP != nil {
if ipv4 := cachedIP.To4(); ipv4 != nil {
@ -402,10 +419,12 @@ func (xTransport *XTransport) resolveAndUpdateCache(host string) error {
if ParseIP(host) != nil {
return nil
}
cachedIP, expired := xTransport.loadCachedIP(host)
if cachedIP != nil && !expired {
cachedIP, expired, updating := xTransport.loadCachedIP(host)
if cachedIP != nil && (!expired || updating) {
return nil
}
xTransport.markUpdatingCachedIP(host)
var foundIP net.IP
var ttl time.Duration
var err error