add comments to alloc

alloc.go

@@ -12,12 +12,14 @@ func init() {
 	defaultAllocator = NewAllocator()
 }
 
-// allocator for incoming frames
-// to prevent write after zeroing
+// 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
@@ -30,6 +32,7 @@ func NewAllocator() *Allocator {
 	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
@@ -43,6 +46,8 @@ func (alloc *Allocator) Get(size int) []byte {
 	}
 }
 
+// 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 {