Vendor main dependencies.

vendor/github.com/juju/ratelimit/ratelimit.go

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+// Copyright 2014 Canonical Ltd.
+// Licensed under the LGPLv3 with static-linking exception.
+// See LICENCE file for details.
+
+// The ratelimit package provides an efficient token bucket implementation
+// that can be used to limit the rate of arbitrary things.
+// See http://en.wikipedia.org/wiki/Token_bucket.
+package ratelimit
+
+import (
+	"math"
+	"strconv"
+	"sync"
+	"time"
+)
+
+// Bucket represents a token bucket that fills at a predetermined rate.
+// Methods on Bucket may be called concurrently.
+type Bucket struct {
+	startTime    time.Time
+	capacity     int64
+	quantum      int64
+	fillInterval time.Duration
+
+	// The mutex guards the fields following it.
+	mu sync.Mutex
+
+	// avail holds the number of available tokens
+	// in the bucket, as of availTick ticks from startTime.
+	// It will be negative when there are consumers
+	// waiting for tokens.
+	avail     int64
+	availTick int64
+}
+
+// NewBucket returns a new token bucket that fills at the
+// rate of one token every fillInterval, up to the given
+// maximum capacity. Both arguments must be
+// positive. The bucket is initially full.
+func NewBucket(fillInterval time.Duration, capacity int64) *Bucket {
+	return NewBucketWithQuantum(fillInterval, capacity, 1)
+}
+
+// rateMargin specifes the allowed variance of actual
+// rate from specified rate. 1% seems reasonable.
+const rateMargin = 0.01
+
+// NewBucketWithRate returns a token bucket that fills the bucket
+// at the rate of rate tokens per second up to the given
+// maximum capacity. Because of limited clock resolution,
+// at high rates, the actual rate may be up to 1% different from the
+// specified rate.
+func NewBucketWithRate(rate float64, capacity int64) *Bucket {
+	for quantum := int64(1); quantum < 1<<50; quantum = nextQuantum(quantum) {
+		fillInterval := time.Duration(1e9 * float64(quantum) / rate)
+		if fillInterval <= 0 {
+			continue
+		}
+		tb := NewBucketWithQuantum(fillInterval, capacity, quantum)
+		if diff := math.Abs(tb.Rate() - rate); diff/rate <= rateMargin {
+			return tb
+		}
+	}
+	panic("cannot find suitable quantum for " + strconv.FormatFloat(rate, 'g', -1, 64))
+}
+
+// nextQuantum returns the next quantum to try after q.
+// We grow the quantum exponentially, but slowly, so we
+// get a good fit in the lower numbers.
+func nextQuantum(q int64) int64 {
+	q1 := q * 11 / 10
+	if q1 == q {
+		q1++
+	}
+	return q1
+}
+
+// NewBucketWithQuantum is similar to NewBucket, but allows
+// the specification of the quantum size - quantum tokens
+// are added every fillInterval.
+func NewBucketWithQuantum(fillInterval time.Duration, capacity, quantum int64) *Bucket {
+	if fillInterval <= 0 {
+		panic("token bucket fill interval is not > 0")
+	}
+	if capacity <= 0 {
+		panic("token bucket capacity is not > 0")
+	}
+	if quantum <= 0 {
+		panic("token bucket quantum is not > 0")
+	}
+	return &Bucket{
+		startTime:    time.Now(),
+		capacity:     capacity,
+		quantum:      quantum,
+		avail:        capacity,
+		fillInterval: fillInterval,
+	}
+}
+
+// Wait takes count tokens from the bucket, waiting until they are
+// available.
+func (tb *Bucket) Wait(count int64) {
+	if d := tb.Take(count); d > 0 {
+		time.Sleep(d)
+	}
+}
+
+// WaitMaxDuration is like Wait except that it will
+// only take tokens from the bucket if it needs to wait
+// for no greater than maxWait. It reports whether
+// any tokens have been removed from the bucket
+// If no tokens have been removed, it returns immediately.
+func (tb *Bucket) WaitMaxDuration(count int64, maxWait time.Duration) bool {
+	d, ok := tb.TakeMaxDuration(count, maxWait)
+	if d > 0 {
+		time.Sleep(d)
+	}
+	return ok
+}
+
+const infinityDuration time.Duration = 0x7fffffffffffffff
+
+// Take takes count tokens from the bucket without blocking. It returns
+// the time that the caller should wait until the tokens are actually
+// available.
+//
+// Note that if the request is irrevocable - there is no way to return
+// tokens to the bucket once this method commits us to taking them.
+func (tb *Bucket) Take(count int64) time.Duration {
+	d, _ := tb.take(time.Now(), count, infinityDuration)
+	return d
+}
+
+// TakeMaxDuration is like Take, except that
+// it will only take tokens from the bucket if the wait
+// time for the tokens is no greater than maxWait.
+//
+// If it would take longer than maxWait for the tokens
+// to become available, it does nothing and reports false,
+// otherwise it returns the time that the caller should
+// wait until the tokens are actually available, and reports
+// true.
+func (tb *Bucket) TakeMaxDuration(count int64, maxWait time.Duration) (time.Duration, bool) {
+	return tb.take(time.Now(), count, maxWait)
+}
+
+// TakeAvailable takes up to count immediately available tokens from the
+// bucket. It returns the number of tokens removed, or zero if there are
+// no available tokens. It does not block.
+func (tb *Bucket) TakeAvailable(count int64) int64 {
+	return tb.takeAvailable(time.Now(), count)
+}
+
+// takeAvailable is the internal version of TakeAvailable - it takes the
+// current time as an argument to enable easy testing.
+func (tb *Bucket) takeAvailable(now time.Time, count int64) int64 {
+	if count <= 0 {
+		return 0
+	}
+	tb.mu.Lock()
+	defer tb.mu.Unlock()
+
+	tb.adjust(now)
+	if tb.avail <= 0 {
+		return 0
+	}
+	if count > tb.avail {
+		count = tb.avail
+	}
+	tb.avail -= count
+	return count
+}
+
+// Available returns the number of available tokens. It will be negative
+// when there are consumers waiting for tokens. Note that if this
+// returns greater than zero, it does not guarantee that calls that take
+// tokens from the buffer will succeed, as the number of available
+// tokens could have changed in the meantime. This method is intended
+// primarily for metrics reporting and debugging.
+func (tb *Bucket) Available() int64 {
+	return tb.available(time.Now())
+}
+
+// available is the internal version of available - it takes the current time as
+// an argument to enable easy testing.
+func (tb *Bucket) available(now time.Time) int64 {
+	tb.mu.Lock()
+	defer tb.mu.Unlock()
+	tb.adjust(now)
+	return tb.avail
+}
+
+// Capacity returns the capacity that the bucket was created with.
+func (tb *Bucket) Capacity() int64 {
+	return tb.capacity
+}
+
+// Rate returns the fill rate of the bucket, in tokens per second.
+func (tb *Bucket) Rate() float64 {
+	return 1e9 * float64(tb.quantum) / float64(tb.fillInterval)
+}
+
+// take is the internal version of Take - it takes the current time as
+// an argument to enable easy testing.
+func (tb *Bucket) take(now time.Time, count int64, maxWait time.Duration) (time.Duration, bool) {
+	if count <= 0 {
+		return 0, true
+	}
+	tb.mu.Lock()
+	defer tb.mu.Unlock()
+
+	currentTick := tb.adjust(now)
+	avail := tb.avail - count
+	if avail >= 0 {
+		tb.avail = avail
+		return 0, true
+	}
+	// Round up the missing tokens to the nearest multiple
+	// of quantum - the tokens won't be available until
+	// that tick.
+	endTick := currentTick + (-avail+tb.quantum-1)/tb.quantum
+	endTime := tb.startTime.Add(time.Duration(endTick) * tb.fillInterval)
+	waitTime := endTime.Sub(now)
+	if waitTime > maxWait {
+		return 0, false
+	}
+	tb.avail = avail
+	return waitTime, true
+}
+
+// adjust adjusts the current bucket capacity based on the current time.
+// It returns the current tick.
+func (tb *Bucket) adjust(now time.Time) (currentTick int64) {
+	currentTick = int64(now.Sub(tb.startTime) / tb.fillInterval)
+
+	if tb.avail >= tb.capacity {
+		return
+	}
+	tb.avail += (currentTick - tb.availTick) * tb.quantum
+	if tb.avail > tb.capacity {
+		tb.avail = tb.capacity
+	}
+	tb.availTick = currentTick
+	return
+}