cloudflared-mirror/h2mux/idletimer.go

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2017-10-16 11:44:03 +00:00
package h2mux
import (
"math/rand"
"sync"
"time"
)
// IdleTimer is a type of Timer designed for managing heartbeats on an idle connection.
// The timer ticks on an interval with added jitter to avoid accidental synchronisation
// between two endpoints. It tracks the number of retries/ticks since the connection was
// last marked active.
//
// The methods of IdleTimer must not be called while a goroutine is reading from C.
type IdleTimer struct {
// The channel on which ticks are delivered.
C <-chan time.Time
// A timer used to measure idle connection time. Reset after sending data.
idleTimer *time.Timer
// The maximum length of time a connection is idle before sending a ping.
idleDuration time.Duration
// A pseudorandom source used to add jitter to the idle duration.
randomSource *rand.Rand
// The maximum number of retries allowed.
maxRetries uint64
// The number of retries since the connection was last marked active.
retries uint64
// A lock to prevent race condition while checking retries
stateLock sync.RWMutex
}
func NewIdleTimer(idleDuration time.Duration, maxRetries uint64) *IdleTimer {
t := &IdleTimer{
idleTimer: time.NewTimer(idleDuration),
idleDuration: idleDuration,
randomSource: rand.New(rand.NewSource(time.Now().Unix())),
maxRetries: maxRetries,
}
t.C = t.idleTimer.C
return t
}
// Retry should be called when retrying the idle timeout. If the maximum number of retries
// has been met, returns false.
// After calling this function and sending a heartbeat, call ResetTimer. Since sending the
// heartbeat could be a blocking operation, we resetting the timer after the write completes
// to avoid it expiring during the write.
func (t *IdleTimer) Retry() bool {
t.stateLock.Lock()
defer t.stateLock.Unlock()
if t.retries >= t.maxRetries {
return false
}
t.retries++
return true
}
func (t *IdleTimer) RetryCount() uint64 {
t.stateLock.RLock()
defer t.stateLock.RUnlock()
return t.retries
}
// MarkActive resets the idle connection timer and suppresses any outstanding idle events.
func (t *IdleTimer) MarkActive() {
if !t.idleTimer.Stop() {
// eat the timer event to prevent spurious pings
<-t.idleTimer.C
}
t.stateLock.Lock()
t.retries = 0
t.stateLock.Unlock()
t.ResetTimer()
}
// Reset the idle timer according to the configured duration, with some added jitter.
func (t *IdleTimer) ResetTimer() {
jitter := time.Duration(t.randomSource.Int63n(int64(t.idleDuration)))
t.idleTimer.Reset(t.idleDuration + jitter)
}