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Published: Feb 9, 2021 License: Apache-2.0 Imports: 5 Imported by: 0



Package rate provides a rate limiter.



Inf is the infinite rate limit; it allows all events (even if burst is zero).

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const InfDuration = time.Duration(1<<63 - 1)

InfDuration is the duration returned by Delay when a Reservation is not OK.


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type Limit

type Limit float64

Limit defines the maximum frequency of some events. Limit is represented as number of events per second. A zero Limit allows no events.

func Every

func Every(interval time.Duration) Limit

Every converts a minimum time interval between events to a Limit.

type Limiter

type Limiter struct {
	// contains filtered or unexported fields

A Limiter controls how frequently events are allowed to happen. It implements a "token bucket" of size b, initially full and refilled at rate r tokens per second. Informally, in any large enough time interval, the Limiter limits the rate to r tokens per second, with a maximum burst size of b events. As a special case, if r == Inf (the infinite rate), b is ignored. See https://en.wikipedia.org/wiki/Token_bucket for more about token buckets.

The zero value is a valid Limiter, but it will reject all events. Use NewLimiter to create non-zero Limiters.

Limiter has three main methods, Allow, Reserve, and Wait. Most callers should use Wait.

Each of the three methods consumes a single token. They differ in their behavior when no token is available. If no token is available, Allow returns false. If no token is available, Reserve returns a reservation for a future token and the amount of time the caller must wait before using it. If no token is available, Wait blocks until one can be obtained or its associated context.Context is canceled.

The methods AllowN, ReserveN, and WaitN consume n tokens.

func NewLimiter

func NewLimiter(r Limit, b int) *Limiter

NewLimiter returns a new Limiter that allows events up to rate r and permits bursts of at most b tokens.

func (*Limiter) Allow

func (lim *Limiter) Allow() bool

Allow is shorthand for AllowN(time.Now(), 1).

func (*Limiter) AllowN

func (lim *Limiter) AllowN(now time.Time, n int) bool

AllowN reports whether n events may happen at time now. Use this method if you intend to drop / skip events that exceed the rate limit. Otherwise use Reserve or Wait.

func (*Limiter) Burst

func (lim *Limiter) Burst() int

Burst returns the maximum burst size. Burst is the maximum number of tokens that can be consumed in a single call to Allow, Reserve, or Wait, so higher Burst values allow more events to happen at once. A zero Burst allows no events, unless limit == Inf.

func (*Limiter) Limit

func (lim *Limiter) Limit() Limit

Limit returns the maximum overall event rate.

func (*Limiter) Reserve

func (lim *Limiter) Reserve() *Reservation

Reserve is shorthand for ReserveN(time.Now(), 1).

func (*Limiter) ReserveN

func (lim *Limiter) ReserveN(now time.Time, n int) *Reservation

ReserveN returns a Reservation that indicates how long the caller must wait before n events happen. The Limiter takes this Reservation into account when allowing future events. ReserveN returns false if n exceeds the Limiter's burst size. Usage example:

r := lim.ReserveN(time.Now(), 1)
if !r.OK() {
  // Not allowed to act! Did you remember to set lim.burst to be > 0 ?

Use this method if you wish to wait and slow down in accordance with the rate limit without dropping events. If you need to respect a deadline or cancel the delay, use Wait instead. To drop or skip events exceeding rate limit, use Allow instead.

func (*Limiter) SetBurst

func (lim *Limiter) SetBurst(newBurst int)

SetBurst is shorthand for SetBurstAt(time.Now(), newBurst).

func (*Limiter) SetBurstAt

func (lim *Limiter) SetBurstAt(now time.Time, newBurst int)

SetBurstAt sets a new burst size for the limiter.

func (*Limiter) SetLimit

func (lim *Limiter) SetLimit(newLimit Limit)

SetLimit is shorthand for SetLimitAt(time.Now(), newLimit).

func (*Limiter) SetLimitAt

func (lim *Limiter) SetLimitAt(now time.Time, newLimit Limit)

SetLimitAt sets a new Limit for the limiter. The new Limit, and Burst, may be violated or underutilized by those which reserved (using Reserve or Wait) but did not yet act before SetLimitAt was called.

func (*Limiter) Wait

func (lim *Limiter) Wait(ctx context.Context) (err error)

Wait is shorthand for WaitN(ctx, 1).

func (*Limiter) WaitN

func (lim *Limiter) WaitN(ctx context.Context, n int) (err error)

WaitN blocks until lim permits n events to happen. It returns an error if n exceeds the Limiter's burst size, the Context is canceled, or the expected wait time exceeds the Context's Deadline. The burst limit is ignored if the rate limit is Inf.

type Reservation

type Reservation struct {
	// contains filtered or unexported fields

A Reservation holds information about events that are permitted by a Limiter to happen after a delay. A Reservation may be canceled, which may enable the Limiter to permit additional events.

func (*Reservation) Cancel

func (r *Reservation) Cancel()

Cancel is shorthand for CancelAt(time.Now()).

func (*Reservation) CancelAt

func (r *Reservation) CancelAt(now time.Time)

CancelAt indicates that the reservation holder will not perform the reserved action and reverses the effects of this Reservation on the rate limit as much as possible, considering that other reservations may have already been made.

func (*Reservation) Delay

func (r *Reservation) Delay() time.Duration

Delay is shorthand for DelayFrom(time.Now()).

func (*Reservation) DelayFrom

func (r *Reservation) DelayFrom(now time.Time) time.Duration

DelayFrom returns the duration for which the reservation holder must wait before taking the reserved action. Zero duration means act immediately. InfDuration means the limiter cannot grant the tokens requested in this Reservation within the maximum wait time.

func (*Reservation) OK

func (r *Reservation) OK() bool

OK returns whether the limiter can provide the requested number of tokens within the maximum wait time. If OK is false, Delay returns InfDuration, and Cancel does nothing.

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