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package statistics
import (
"math"
"sync"
"time"
"github.com/matrix-org/dendrite/federationsender/storage"
"github.com/matrix-org/gomatrixserverlib"
"github.com/sirupsen/logrus"
"go.uber.org/atomic"
)
// 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,
}
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
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)))
}
// 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.successCounter.Add(1)
s.backoffStarted.Store(false)
s.backoffCount.Store(0)
s.blacklisted.Store(false)
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. Reset the counter to 0 so that
// we backoff only for short periods of time to start with.
if s.backoffStarted.CAS(false, true) {
s.backoffCount.Store(0)
}
// 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
}
// BackoffIfRequired will block for as long as the current
// backoff requires, if needed. Otherwise it will do nothing.
func (s *ServerStatistics) BackoffIfRequired(backingOff atomic.Bool, interrupt <-chan bool) (time.Duration, bool) {
if started := s.backoffStarted.Load(); !started {
return 0, false
}
// Work out if we should be blacklisting at this point.
count := s.backoffCount.Inc()
if count >= s.statistics.FailuresUntilBlacklist {
// We've exceeded the maximum amount of times we're willing
// to back off, which is probably in the region of hours by
// now. Mark the host as blacklisted and tell the caller to
// give up.
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 0, true
}
// Work out when we should wait until.
duration := s.duration(count)
until := time.Now().Add(duration)
s.backoffUntil.Store(until)
// Notify the destination queue that we're backing off now.
backingOff.Store(true)
defer backingOff.Store(false)
// Work out how long we should be backing off for.
logrus.Warnf("Backing off %q for %s", s.serverName, duration)
// Wait for either an interruption or for the backoff to
// complete.
select {
case <-interrupt:
logrus.Debugf("Interrupting backoff for %q", s.serverName)
case <-time.After(duration):
}
return duration, false
}
// 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()
}
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