// Get returns the cached resolver, first updating the cached
// value if it's stale. If reloading fails, the previous value
// is used.
func (dns *DNSResolver) Get() net.IP {
// Every UDP DNS port forward frequently calls Get(), so this code
// is intended to minimize blocking. Most callers will hit just the
// atomic.LoadInt64 reload time check and the RLock (an atomic.AddInt32
// when no write lock is pending). An atomic.CompareAndSwapInt32 is
// used to ensure only one goroutine enters Reload() and blocks on
// its write lock. Finally, since since ReloadableFile.Reload
// checks whether the underlying file has changed _before_ aquiring a
// write lock, we only incur write lock blocking when "/etc/resolv.conf"
// has actually changed.
lastReloadTime := monotime.Time(atomic.LoadInt64(&dns.lastReloadTime))
stale := monotime.Now().After(lastReloadTime.Add(DNS_SYSTEM_CONFIG_RELOAD_PERIOD))
if stale {
isReloader := atomic.CompareAndSwapInt32(&dns.isReloading, 0, 1)
if isReloader {
// Unconditionally set last reload time. Even on failure only
// want to retry after another DNS_SYSTEM_CONFIG_RELOAD_PERIOD.
atomic.StoreInt64(&dns.lastReloadTime, time.Now().Unix())
_, err := dns.Reload()
if err != nil {
log.WithContextFields(
LogFields{"err": err}).Info(
"failed to reload system DNS resolver")
}
atomic.StoreInt32(&dns.isReloading, 0)
}
}
dns.ReloadableFile.RLock()
defer dns.ReloadableFile.RUnlock()
return dns.resolver
}
func (session *meekSession) expired() bool {
lastActivity := monotime.Time(atomic.LoadInt64(&session.lastActivity))
return monotime.Since(lastActivity) > MEEK_MAX_SESSION_STALENESS
}
// GetLastActivityTime returns the arbitrary monotonic time of the last Read.
func (conn *ActivityMonitoredConn) GetLastActivityMonotime() monotime.Time {
return monotime.Time(atomic.LoadInt64(&conn.lastReadActivityTime))
}