Improve: pool buffer alloc

common/pool/alloc.go

@@ -0,0 +1,65 @@
+package pool
+
+// Inspired by https://github.com/xtaci/smux/blob/master/alloc.go
+
+import (
+	"errors"
+	"math/bits"
+	"sync"
+)
+
+var defaultAllocator *Allocator
+
+func init() {
+	defaultAllocator = NewAllocator()
+}
+
+// Allocator for incoming frames, optimized to prevent overwriting after zeroing
+type Allocator struct {
+	buffers []sync.Pool
+}
+
+// NewAllocator initiates a []byte allocator for frames less than 65536 bytes,
+// the waste(memory fragmentation) of space allocation is guaranteed to be
+// no more than 50%.
+func NewAllocator() *Allocator {
+	alloc := new(Allocator)
+	alloc.buffers = make([]sync.Pool, 17) // 1B -> 64K
+	for k := range alloc.buffers {
+		i := k
+		alloc.buffers[k].New = func() interface{} {
+			return make([]byte, 1<<uint32(i))
+		}
+	}
+	return alloc
+}
+
+// Get a []byte from pool with most appropriate cap
+func (alloc *Allocator) Get(size int) []byte {
+	if size <= 0 || size > 65536 {
+		return nil
+	}
+
+	bits := msb(size)
+	if size == 1<<bits {
+		return alloc.buffers[bits].Get().([]byte)[:size]
+	}
+
+	return alloc.buffers[bits+1].Get().([]byte)[:size]
+}
+
+// Put returns a []byte to pool for future use,
+// which the cap must be exactly 2^n
+func (alloc *Allocator) Put(buf []byte) error {
+	bits := msb(cap(buf))
+	if cap(buf) == 0 || cap(buf) > 65536 || cap(buf) != 1<<bits {
+		return errors.New("allocator Put() incorrect buffer size")
+	}
+	alloc.buffers[bits].Put(buf)
+	return nil
+}
+
+// msb return the pos of most significiant bit
+func msb(size int) uint16 {
+	return uint16(bits.Len32(uint32(size)) - 1)
+}