initial commit

vendor/github.com/valyala/bytebufferpool/pool.go

@@ -0,0 +1,151 @@
+package bytebufferpool
+
+import (
+	"sort"
+	"sync"
+	"sync/atomic"
+)
+
+const (
+	minBitSize = 6 // 2**6=64 is a CPU cache line size
+	steps      = 20
+
+	minSize = 1 << minBitSize
+	maxSize = 1 << (minBitSize + steps - 1)
+
+	calibrateCallsThreshold = 42000
+	maxPercentile           = 0.95
+)
+
+// Pool represents byte buffer pool.
+//
+// Distinct pools may be used for distinct types of byte buffers.
+// Properly determined byte buffer types with their own pools may help reducing
+// memory waste.
+type Pool struct {
+	calls       [steps]uint64
+	calibrating uint64
+
+	defaultSize uint64
+	maxSize     uint64
+
+	pool sync.Pool
+}
+
+var defaultPool Pool
+
+// Get returns an empty byte buffer from the pool.
+//
+// Got byte buffer may be returned to the pool via Put call.
+// This reduces the number of memory allocations required for byte buffer
+// management.
+func Get() *ByteBuffer { return defaultPool.Get() }
+
+// Get returns new byte buffer with zero length.
+//
+// The byte buffer may be returned to the pool via Put after the use
+// in order to minimize GC overhead.
+func (p *Pool) Get() *ByteBuffer {
+	v := p.pool.Get()
+	if v != nil {
+		return v.(*ByteBuffer)
+	}
+	return &ByteBuffer{
+		B: make([]byte, 0, atomic.LoadUint64(&p.defaultSize)),
+	}
+}
+
+// Put returns byte buffer to the pool.
+//
+// ByteBuffer.B mustn't be touched after returning it to the pool.
+// Otherwise data races will occur.
+func Put(b *ByteBuffer) { defaultPool.Put(b) }
+
+// Put releases byte buffer obtained via Get to the pool.
+//
+// The buffer mustn't be accessed after returning to the pool.
+func (p *Pool) Put(b *ByteBuffer) {
+	idx := index(len(b.B))
+
+	if atomic.AddUint64(&p.calls[idx], 1) > calibrateCallsThreshold {
+		p.calibrate()
+	}
+
+	maxSize := int(atomic.LoadUint64(&p.maxSize))
+	if maxSize == 0 || cap(b.B) <= maxSize {
+		b.Reset()
+		p.pool.Put(b)
+	}
+}
+
+func (p *Pool) calibrate() {
+	if !atomic.CompareAndSwapUint64(&p.calibrating, 0, 1) {
+		return
+	}
+
+	a := make(callSizes, 0, steps)
+	var callsSum uint64
+	for i := uint64(0); i < steps; i++ {
+		calls := atomic.SwapUint64(&p.calls[i], 0)
+		callsSum += calls
+		a = append(a, callSize{
+			calls: calls,
+			size:  minSize << i,
+		})
+	}
+	sort.Sort(a)
+
+	defaultSize := a[0].size
+	maxSize := defaultSize
+
+	maxSum := uint64(float64(callsSum) * maxPercentile)
+	callsSum = 0
+	for i := 0; i < steps; i++ {
+		if callsSum > maxSum {
+			break
+		}
+		callsSum += a[i].calls
+		size := a[i].size
+		if size > maxSize {
+			maxSize = size
+		}
+	}
+
+	atomic.StoreUint64(&p.defaultSize, defaultSize)
+	atomic.StoreUint64(&p.maxSize, maxSize)
+
+	atomic.StoreUint64(&p.calibrating, 0)
+}
+
+type callSize struct {
+	calls uint64
+	size  uint64
+}
+
+type callSizes []callSize
+
+func (ci callSizes) Len() int {
+	return len(ci)
+}
+
+func (ci callSizes) Less(i, j int) bool {
+	return ci[i].calls > ci[j].calls
+}
+
+func (ci callSizes) Swap(i, j int) {
+	ci[i], ci[j] = ci[j], ci[i]
+}
+
+func index(n int) int {
+	n--
+	n >>= minBitSize
+	idx := 0
+	for n > 0 {
+		n >>= 1
+		idx++
+	}
+	if idx >= steps {
+		idx = steps - 1
+	}
+	return idx
+}