package statistics import ( "math" "sync" "time" "github.com/matrix-org/gomatrixserverlib" "github.com/sirupsen/logrus" "go.uber.org/atomic" "github.com/matrix-org/dendrite/federationapi/storage" ) // Statistics contains information about all of the remote federated // hosts that we have interacted with. It is basically a threadsafe // wrapper. type Statistics struct { DB storage.Database servers map[gomatrixserverlib.ServerName]*ServerStatistics mutex sync.RWMutex // How many times should we tolerate consecutive failures before we // just blacklist the host altogether? The backoff is exponential, // so the max time here to attempt is 2**failures seconds. FailuresUntilBlacklist uint32 } // ForServer returns server statistics for the given server name. If it // does not exist, it will create empty statistics and return those. func (s *Statistics) ForServer(serverName gomatrixserverlib.ServerName) *ServerStatistics { // If the map hasn't been initialised yet then do that. if s.servers == nil { s.mutex.Lock() s.servers = make(map[gomatrixserverlib.ServerName]*ServerStatistics) s.mutex.Unlock() } // Look up if we have statistics for this server already. s.mutex.RLock() server, found := s.servers[serverName] s.mutex.RUnlock() // If we don't, then make one. if !found { s.mutex.Lock() server = &ServerStatistics{ statistics: s, serverName: serverName, interrupt: make(chan struct{}), } s.servers[serverName] = server s.mutex.Unlock() blacklisted, err := s.DB.IsServerBlacklisted(serverName) if err != nil { logrus.WithError(err).Errorf("Failed to get blacklist entry %q", serverName) } else { server.blacklisted.Store(blacklisted) } } return server } // ServerStatistics contains information about our interactions with a // remote federated host, e.g. how many times we were successful, how // many times we failed etc. It also manages the backoff time and black- // listing a remote host if it remains uncooperative. type ServerStatistics struct { statistics *Statistics // serverName gomatrixserverlib.ServerName // blacklisted atomic.Bool // is the node blacklisted backoffStarted atomic.Bool // is the backoff started backoffUntil atomic.Value // time.Time until this backoff interval ends backoffCount atomic.Uint32 // number of times BackoffDuration has been called interrupt chan struct{} // interrupts the backoff goroutine successCounter atomic.Uint32 // how many times have we succeeded? } // duration returns how long the next backoff interval should be. func (s *ServerStatistics) duration(count uint32) time.Duration { return time.Second * time.Duration(math.Exp2(float64(count))) } // cancel will interrupt the currently active backoff. func (s *ServerStatistics) cancel() { s.blacklisted.Store(false) s.backoffUntil.Store(time.Time{}) select { case s.interrupt <- struct{}{}: default: } } // Success updates the server statistics with a new successful // attempt, which increases the sent counter and resets the idle and // failure counters. If a host was blacklisted at this point then // we will unblacklist it. func (s *ServerStatistics) Success() { s.cancel() s.successCounter.Inc() s.backoffCount.Store(0) if s.statistics.DB != nil { if err := s.statistics.DB.RemoveServerFromBlacklist(s.serverName); err != nil { logrus.WithError(err).Errorf("Failed to remove %q from blacklist", s.serverName) } } } // Failure marks a failure and starts backing off if needed. // The next call to BackoffIfRequired will do the right thing // after this. It will return the time that the current failure // will result in backoff waiting until, and a bool signalling // whether we have blacklisted and therefore to give up. func (s *ServerStatistics) Failure() (time.Time, bool) { // If we aren't already backing off, this call will start // a new backoff period. Increase the failure counter and // start a goroutine which will wait out the backoff and // unset the backoffStarted flag when done. if s.backoffStarted.CAS(false, true) { if s.backoffCount.Inc() >= s.statistics.FailuresUntilBlacklist { s.blacklisted.Store(true) if s.statistics.DB != nil { if err := s.statistics.DB.AddServerToBlacklist(s.serverName); err != nil { logrus.WithError(err).Errorf("Failed to add %q to blacklist", s.serverName) } } return time.Time{}, true } go func() { until, ok := s.backoffUntil.Load().(time.Time) if ok && !until.IsZero() { select { case <-time.After(time.Until(until)): case <-s.interrupt: } s.backoffStarted.Store(false) } }() } // Check if we have blacklisted this node. if s.blacklisted.Load() { return time.Now(), true } // If we're already backing off and we haven't yet surpassed // the deadline then return that. Repeated calls to Failure // within a single backoff interval will have no side effects. if until, ok := s.backoffUntil.Load().(time.Time); ok && !time.Now().After(until) { return until, false } // We're either backing off and have passed the deadline, or // we aren't backing off, so work out what the next interval // will be. count := s.backoffCount.Load() until := time.Now().Add(s.duration(count)) s.backoffUntil.Store(until) return until, false } // BackoffInfo returns information about the current or previous backoff. // Returns the last backoffUntil time and whether the server is currently blacklisted or not. func (s *ServerStatistics) BackoffInfo() (*time.Time, bool) { until, ok := s.backoffUntil.Load().(time.Time) if ok { return &until, s.blacklisted.Load() } return nil, s.blacklisted.Load() } // Blacklisted returns true if the server is blacklisted and false // otherwise. func (s *ServerStatistics) Blacklisted() bool { return s.blacklisted.Load() } // SuccessCount returns the number of successful requests. This is // usually useful in constructing transaction IDs. func (s *ServerStatistics) SuccessCount() uint32 { return s.successCounter.Load() }