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frequency_counter.go
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frequency_counter.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 xcounter
import (
"math"
"sync"
"sync/atomic"
"time"
"github.com/m3db/m3x/clock"
)
type frequencyBucket struct {
sync.RWMutex
timestamp time.Time
count int64
}
// record records the frequency value n for a given time.
// If the frequency value is too old, it's discarded.
// Returns true if the value is processed, false if it
// requires further processing.
func (b *frequencyBucket) record(t time.Time, n int64) {
b.RLock()
if processed := b.recordWithLock(t, n); processed {
b.RUnlock()
return
}
b.RUnlock()
b.Lock()
if processed := b.recordWithLock(t, n); processed {
b.Unlock()
return
}
b.timestamp = t
b.count = n
b.Unlock()
}
// countFor returns the frequency value if the bucket
// timestamp matches the given time, 0 otherwise
func (b *frequencyBucket) countFor(t time.Time) int64 {
b.RLock()
if b.timestamp != t {
b.RUnlock()
return 0
}
count := b.count
b.RUnlock()
return count
}
func (b *frequencyBucket) recordWithLock(t time.Time, n int64) bool {
// The information is too old to keep
if t.Before(b.timestamp) {
return true
}
// The timestamp matches so it's safe to record
if t.Equal(b.timestamp) {
// NB(xichen): use atomics here so multiple goroutines
// can record at the same time
atomic.AddInt64(&b.count, n)
return true
}
// Otherwise this bucket is stale, don't record
return false
}
// FrequencyCounter keeps track of the frequency counts for the
// previous interval and the current interval
type FrequencyCounter struct {
nowFn clock.NowFn
interval time.Duration
buckets []frequencyBucket
}
// NewFrequencyCounter creates a new frequency counter
func NewFrequencyCounter(opts Options) FrequencyCounter {
return FrequencyCounter{
nowFn: time.Now,
interval: opts.Interval(),
buckets: make([]frequencyBucket, opts.NumBuckets()),
}
}
// Record records a frequency value in the corresponding bucket
func (c *FrequencyCounter) Record(n int64) {
now := c.nowFn().Truncate(c.interval)
bucketIdx := c.bucketIdx(now)
c.buckets[bucketIdx].record(now, n)
}
// Count returns the frequency count between now - dur and now
func (c *FrequencyCounter) Count(dur time.Duration) int64 {
if dur <= 0 {
return 0
}
var (
n = int(math.Min(float64(dur/c.interval), float64(len(c.buckets))))
now = c.nowFn().Truncate(c.interval)
currIdx = c.bucketIdx(now)
currTime = now
total int64
)
// NB(xichen): we discount the current bucket because it may be incomplete
for i := 0; i < n; i++ {
currTime = currTime.Add(-c.interval)
currIdx--
if currIdx < 0 {
currIdx += len(c.buckets)
}
total += c.buckets[currIdx].countFor(currTime)
}
return total
}
func (c *FrequencyCounter) bucketIdx(now time.Time) int {
return int((now.UnixNano() / int64(c.interval)) % int64(len(c.buckets)))
}