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|
package smux
import (
"errors"
"sync"
)
var (
defaultAllocator *Allocator
debruijinPos = [...]byte{0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30, 8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31}
)
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]
} else {
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
// http://supertech.csail.mit.edu/papers/debruijn.pdf
func msb(size int) byte {
v := uint32(size)
v |= v >> 1
v |= v >> 2
v |= v >> 4
v |= v >> 8
v |= v >> 16
return debruijinPos[(v*0x07C4ACDD)>>27]
}
|
