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@ -80,6 +80,19 @@ func (lim *Limiter) Burst() int {
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return lim.burst
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}
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// TokensAt returns the number of tokens available at time t.
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func (lim *Limiter) TokensAt(t time.Time) float64 {
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lim.mu.Lock()
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_, _, tokens := lim.advance(t) // does not mutute lim
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lim.mu.Unlock()
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return tokens
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}
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// Tokens returns the number of tokens available now.
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func (lim *Limiter) Tokens() float64 {
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return lim.TokensAt(time.Now())
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}
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// NewLimiter returns a new Limiter that allows events up to rate r and permits
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// bursts of at most b tokens.
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func NewLimiter(r Limit, b int) *Limiter {
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@ -89,16 +102,16 @@ func NewLimiter(r Limit, b int) *Limiter {
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}
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}
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// Allow is shorthand for AllowN(time.Now(), 1).
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// Allow reports whether an event may happen now.
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func (lim *Limiter) Allow() bool {
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return lim.AllowN(time.Now(), 1)
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}
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// AllowN reports whether n events may happen at time now.
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// AllowN reports whether n events may happen at time t.
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// Use this method if you intend to drop / skip events that exceed the rate limit.
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// Otherwise use Reserve or Wait.
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func (lim *Limiter) AllowN(now time.Time, n int) bool {
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return lim.reserveN(now, n, 0).ok
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func (lim *Limiter) AllowN(t time.Time, n int) bool {
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return lim.reserveN(t, n, 0).ok
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}
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// A Reservation holds information about events that are permitted by a Limiter to happen after a delay.
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@ -125,17 +138,17 @@ func (r *Reservation) Delay() time.Duration {
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}
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// InfDuration is the duration returned by Delay when a Reservation is not OK.
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const InfDuration = time.Duration(1<<63 - 1)
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const InfDuration = time.Duration(math.MaxInt64)
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// DelayFrom returns the duration for which the reservation holder must wait
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// before taking the reserved action. Zero duration means act immediately.
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// InfDuration means the limiter cannot grant the tokens requested in this
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// Reservation within the maximum wait time.
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func (r *Reservation) DelayFrom(now time.Time) time.Duration {
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func (r *Reservation) DelayFrom(t time.Time) time.Duration {
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if !r.ok {
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return InfDuration
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}
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delay := r.timeToAct.Sub(now)
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delay := r.timeToAct.Sub(t)
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if delay < 0 {
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return 0
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}
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@ -150,7 +163,7 @@ func (r *Reservation) Cancel() {
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// CancelAt indicates that the reservation holder will not perform the reserved action
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// and reverses the effects of this Reservation on the rate limit as much as possible,
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// considering that other reservations may have already been made.
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func (r *Reservation) CancelAt(now time.Time) {
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func (r *Reservation) CancelAt(t time.Time) {
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if !r.ok {
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return
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}
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@ -158,7 +171,7 @@ func (r *Reservation) CancelAt(now time.Time) {
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r.lim.mu.Lock()
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defer r.lim.mu.Unlock()
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if r.lim.limit == Inf || r.tokens == 0 || r.timeToAct.Before(now) {
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if r.lim.limit == Inf || r.tokens == 0 || r.timeToAct.Before(t) {
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return
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}
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@ -170,18 +183,18 @@ func (r *Reservation) CancelAt(now time.Time) {
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return
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}
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// advance time to now
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now, _, tokens := r.lim.advance(now)
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t, _, tokens := r.lim.advance(t)
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// calculate new number of tokens
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tokens += restoreTokens
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if burst := float64(r.lim.burst); tokens > burst {
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tokens = burst
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}
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// update state
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r.lim.last = now
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r.lim.last = t
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r.lim.tokens = tokens
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if r.timeToAct == r.lim.lastEvent {
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prevEvent := r.timeToAct.Add(r.limit.durationFromTokens(float64(-r.tokens)))
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if !prevEvent.Before(now) {
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if !prevEvent.Before(t) {
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r.lim.lastEvent = prevEvent
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}
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}
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@ -196,6 +209,7 @@ func (lim *Limiter) Reserve() *Reservation {
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// The Limiter takes this Reservation into account when allowing future events.
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// The returned Reservation’s OK() method returns false if n exceeds the Limiter's burst size.
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// Usage example:
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//
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// r := lim.ReserveN(time.Now(), 1)
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// if !r.OK() {
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// // Not allowed to act! Did you remember to set lim.burst to be > 0 ?
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@ -203,11 +217,12 @@ func (lim *Limiter) Reserve() *Reservation {
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// }
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// time.Sleep(r.Delay())
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// Act()
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//
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// Use this method if you wish to wait and slow down in accordance with the rate limit without dropping events.
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// If you need to respect a deadline or cancel the delay, use Wait instead.
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// To drop or skip events exceeding rate limit, use Allow instead.
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func (lim *Limiter) ReserveN(now time.Time, n int) *Reservation {
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r := lim.reserveN(now, n, InfDuration)
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func (lim *Limiter) ReserveN(t time.Time, n int) *Reservation {
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r := lim.reserveN(t, n, InfDuration)
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return &r
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}
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@ -221,6 +236,18 @@ func (lim *Limiter) Wait(ctx context.Context) (err error) {
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// canceled, or the expected wait time exceeds the Context's Deadline.
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// The burst limit is ignored if the rate limit is Inf.
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func (lim *Limiter) WaitN(ctx context.Context, n int) (err error) {
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// The test code calls lim.wait with a fake timer generator.
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// This is the real timer generator.
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newTimer := func(d time.Duration) (<-chan time.Time, func() bool, func()) {
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timer := time.NewTimer(d)
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return timer.C, timer.Stop, func() {}
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}
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return lim.wait(ctx, n, time.Now(), newTimer)
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}
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// wait is the internal implementation of WaitN.
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func (lim *Limiter) wait(ctx context.Context, n int, t time.Time, newTimer func(d time.Duration) (<-chan time.Time, func() bool, func())) error {
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lim.mu.Lock()
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burst := lim.burst
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limit := lim.limit
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@ -236,25 +263,25 @@ func (lim *Limiter) WaitN(ctx context.Context, n int) (err error) {
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default:
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}
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// Determine wait limit
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now := time.Now()
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waitLimit := InfDuration
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if deadline, ok := ctx.Deadline(); ok {
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waitLimit = deadline.Sub(now)
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waitLimit = deadline.Sub(t)
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}
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// Reserve
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r := lim.reserveN(now, n, waitLimit)
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r := lim.reserveN(t, n, waitLimit)
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if !r.ok {
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return fmt.Errorf("rate: Wait(n=%d) would exceed context deadline", n)
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}
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// Wait if necessary
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delay := r.DelayFrom(now)
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delay := r.DelayFrom(t)
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if delay == 0 {
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return nil
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}
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t := time.NewTimer(delay)
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defer t.Stop()
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ch, stop, advance := newTimer(delay)
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defer stop()
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advance() // only has an effect when testing
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select {
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case <-t.C:
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case <-ch:
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// We can proceed.
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return nil
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case <-ctx.Done():
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@ -273,13 +300,13 @@ func (lim *Limiter) SetLimit(newLimit Limit) {
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// SetLimitAt sets a new Limit for the limiter. The new Limit, and Burst, may be violated
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// or underutilized by those which reserved (using Reserve or Wait) but did not yet act
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// before SetLimitAt was called.
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func (lim *Limiter) SetLimitAt(now time.Time, newLimit Limit) {
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func (lim *Limiter) SetLimitAt(t time.Time, newLimit Limit) {
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lim.mu.Lock()
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defer lim.mu.Unlock()
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now, _, tokens := lim.advance(now)
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t, _, tokens := lim.advance(t)
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lim.last = now
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lim.last = t
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lim.tokens = tokens
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lim.limit = newLimit
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}
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@ -290,13 +317,13 @@ func (lim *Limiter) SetBurst(newBurst int) {
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}
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// SetBurstAt sets a new burst size for the limiter.
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func (lim *Limiter) SetBurstAt(now time.Time, newBurst int) {
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func (lim *Limiter) SetBurstAt(t time.Time, newBurst int) {
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lim.mu.Lock()
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defer lim.mu.Unlock()
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now, _, tokens := lim.advance(now)
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t, _, tokens := lim.advance(t)
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lim.last = now
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lim.last = t
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lim.tokens = tokens
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lim.burst = newBurst
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}
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@ -304,20 +331,32 @@ func (lim *Limiter) SetBurstAt(now time.Time, newBurst int) {
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// reserveN is a helper method for AllowN, ReserveN, and WaitN.
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// maxFutureReserve specifies the maximum reservation wait duration allowed.
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// reserveN returns Reservation, not *Reservation, to avoid allocation in AllowN and WaitN.
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func (lim *Limiter) reserveN(now time.Time, n int, maxFutureReserve time.Duration) Reservation {
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func (lim *Limiter) reserveN(t time.Time, n int, maxFutureReserve time.Duration) Reservation {
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lim.mu.Lock()
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defer lim.mu.Unlock()
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if lim.limit == Inf {
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lim.mu.Unlock()
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return Reservation{
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ok: true,
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lim: lim,
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tokens: n,
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timeToAct: now,
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timeToAct: t,
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}
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} else if lim.limit == 0 {
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var ok bool
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if lim.burst >= n {
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ok = true
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lim.burst -= n
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}
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return Reservation{
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ok: ok,
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lim: lim,
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tokens: lim.burst,
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timeToAct: t,
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}
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}
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now, last, tokens := lim.advance(now)
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t, last, tokens := lim.advance(t)
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// Calculate the remaining number of tokens resulting from the request.
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tokens -= float64(n)
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@ -339,44 +378,46 @@ func (lim *Limiter) reserveN(now time.Time, n int, maxFutureReserve time.Duratio
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}
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if ok {
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r.tokens = n
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r.timeToAct = now.Add(waitDuration)
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r.timeToAct = t.Add(waitDuration)
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}
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// Update state
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if ok {
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lim.last = now
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lim.last = t
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lim.tokens = tokens
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lim.lastEvent = r.timeToAct
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} else {
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lim.last = last
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}
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lim.mu.Unlock()
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return r
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}
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// advance calculates and returns an updated state for lim resulting from the passage of time.
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// lim is not changed.
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// advance requires that lim.mu is held.
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func (lim *Limiter) advance(now time.Time) (newNow time.Time, newLast time.Time, newTokens float64) {
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func (lim *Limiter) advance(t time.Time) (newT time.Time, newLast time.Time, newTokens float64) {
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last := lim.last
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if now.Before(last) {
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last = now
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if t.Before(last) {
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last = t
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}
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|
|
// Calculate the new number of tokens, due to time that passed.
|
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|
|
elapsed := now.Sub(last)
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|
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elapsed := t.Sub(last)
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|
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delta := lim.limit.tokensFromDuration(elapsed)
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tokens := lim.tokens + delta
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|
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if burst := float64(lim.burst); tokens > burst {
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tokens = burst
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}
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|
return now, last, tokens
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return t, last, tokens
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}
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|
|
// durationFromTokens is a unit conversion function from the number of tokens to the duration
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|
|
// of time it takes to accumulate them at a rate of limit tokens per second.
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|
|
func (limit Limit) durationFromTokens(tokens float64) time.Duration {
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|
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if limit <= 0 {
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return InfDuration
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}
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|
|
seconds := tokens / float64(limit)
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|
|
return time.Duration(float64(time.Second) * seconds)
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}
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|
|
@ -384,5 +425,8 @@ func (limit Limit) durationFromTokens(tokens float64) time.Duration {
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|
|
// tokensFromDuration is a unit conversion function from a time duration to the number of tokens
|
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|
|
// which could be accumulated during that duration at a rate of limit tokens per second.
|
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|
|
func (limit Limit) tokensFromDuration(d time.Duration) float64 {
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|
|
if limit <= 0 {
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|
|
return 0
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|
|
}
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|
|
return d.Seconds() * float64(limit)
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}
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Sebastiaan van Stijn