github.com/xxf098/lite-proxy@v0.15.1-0.20230422081941-12c69f323218/common/pool/alloc.go (about)

     1  package pool
     2  
     3  // Inspired by https://github.com/xtaci/smux/blob/master/alloc.go
     4  
     5  import (
     6  	"errors"
     7  	"math/bits"
     8  	"sync"
     9  )
    10  
    11  var defaultAllocator *Allocator
    12  
    13  func init() {
    14  	defaultAllocator = NewAllocator()
    15  }
    16  
    17  // Allocator for incoming frames, optimized to prevent overwriting after zeroing
    18  type Allocator struct {
    19  	buffers []sync.Pool
    20  }
    21  
    22  // NewAllocator initiates a []byte allocator for frames less than 65536 bytes,
    23  // the waste(memory fragmentation) of space allocation is guaranteed to be
    24  // no more than 50%.
    25  func NewAllocator() *Allocator {
    26  	alloc := new(Allocator)
    27  	alloc.buffers = make([]sync.Pool, 17) // 1B -> 64K
    28  	for k := range alloc.buffers {
    29  		i := k
    30  		alloc.buffers[k].New = func() interface{} {
    31  			return make([]byte, 1<<uint32(i))
    32  		}
    33  	}
    34  	return alloc
    35  }
    36  
    37  // Get a []byte from pool with most appropriate cap
    38  func (alloc *Allocator) Get(size int) []byte {
    39  	if size <= 0 || size > 65536 {
    40  		return nil
    41  	}
    42  
    43  	bits := msb(size)
    44  	if size == 1<<bits {
    45  		return alloc.buffers[bits].Get().([]byte)[:size]
    46  	}
    47  
    48  	return alloc.buffers[bits+1].Get().([]byte)[:size]
    49  }
    50  
    51  // Put returns a []byte to pool for future use,
    52  // which the cap must be exactly 2^n
    53  func (alloc *Allocator) Put(buf []byte) error {
    54  	bits := msb(cap(buf))
    55  	if cap(buf) == 0 || cap(buf) > 65536 || cap(buf) != 1<<bits {
    56  		return errors.New("allocator Put() incorrect buffer size")
    57  	}
    58  
    59  	//lint:ignore SA6002 ignore temporarily
    60  	alloc.buffers[bits].Put(buf)
    61  	return nil
    62  }
    63  
    64  // msb return the pos of most significant bit
    65  func msb(size int) uint16 {
    66  	return uint16(bits.Len32(uint32(size)) - 1)
    67  }