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limiter.go
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limiter.go
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// Copyright (c) 2017 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
package rate
import (
"sync"
"sync/atomic"
"time"
"github.com/m3db/m3/src/x/clock"
)
var (
zeroTime = time.Unix(0, 0)
)
// Limiter is a simple rate limiter to control how frequently events are allowed to happen.
type Limiter struct {
sync.RWMutex
limitPerSecond int64
nowFn clock.NowFn
alignedLast time.Time
allowed int64
}
// NewLimiter creates a new rate limiter.
func NewLimiter(l int64, fn clock.NowFn) *Limiter {
return &Limiter{
limitPerSecond: l,
nowFn: fn,
}
}
// Limit returns the current limit.
func (l *Limiter) Limit() int64 {
l.RLock()
limit := l.limitPerSecond
l.RUnlock()
return limit
}
// IsAllowed returns whether n events may happen now.
// NB(xichen): If a large request comes in, this could potentially block following
// requests in the same second from going through. This is a non-issue if the limit
// is much bigger than the typical batch size, which is indeed the case in the aggregation
// layer as each batch size is usually fairly small.
func (l *Limiter) IsAllowed(n int64) bool {
alignedNow := l.nowFn().Truncate(time.Second)
l.RLock()
if !alignedNow.After(l.alignedLast) {
isAllowed := atomic.AddInt64(&l.allowed, n) <= l.limitPerSecond
l.RUnlock()
return isAllowed
}
l.RUnlock()
l.Lock()
if !alignedNow.After(l.alignedLast) {
isAllowed := atomic.AddInt64(&l.allowed, n) <= l.limitPerSecond
l.Unlock()
return isAllowed
}
l.alignedLast = alignedNow
l.allowed = n
isAllowed := l.allowed <= l.limitPerSecond
l.Unlock()
return isAllowed
}
// Reset resets the internal state.
func (l *Limiter) Reset(limit int64) {
l.Lock()
l.alignedLast = zeroTime
l.allowed = 0
l.limitPerSecond = limit
l.Unlock()
}