github.com/zuoyebang/bitalosdb@v1.1.1-0.20240516111551-79a8c4d8ce20/internal/arenaskl/arena.go (about)

     1  // Copyright 2021 The Bitalosdb author(hustxrb@163.com) and other contributors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package arenaskl
    16  
    17  import (
    18  	"errors"
    19  	"math"
    20  	"sync/atomic"
    21  	"unsafe"
    22  )
    23  
    24  type Arena struct {
    25  	n   uint64
    26  	buf []byte
    27  }
    28  
    29  const (
    30  	align4 = 3
    31  )
    32  
    33  var (
    34  	ErrArenaFull = errors.New("allocation failed because arena is full")
    35  )
    36  
    37  func NewArena(buf []byte) *Arena {
    38  	return &Arena{
    39  		n:   1,
    40  		buf: buf,
    41  	}
    42  }
    43  
    44  func (a *Arena) Size() uint32 {
    45  	s := atomic.LoadUint64(&a.n)
    46  	if s > math.MaxUint32 {
    47  		return math.MaxUint32
    48  	}
    49  	return uint32(s)
    50  }
    51  
    52  func (a *Arena) Capacity() uint32 {
    53  	return uint32(len(a.buf))
    54  }
    55  
    56  func (a *Arena) alloc(size, align, overflow uint32) (uint32, uint32, error) {
    57  	origSize := atomic.LoadUint64(&a.n)
    58  	if int(origSize) > len(a.buf) {
    59  		return 0, 0, ErrArenaFull
    60  	}
    61  
    62  	padded := size + align
    63  
    64  	newSize := atomic.AddUint64(&a.n, uint64(padded))
    65  	if int(newSize)+int(overflow) > len(a.buf) {
    66  		return 0, 0, ErrArenaFull
    67  	}
    68  
    69  	offset := (uint32(newSize) - padded + align) & ^align
    70  	return offset, padded, nil
    71  }
    72  
    73  func (a *Arena) getBytes(offset uint32, size uint32) []byte {
    74  	if offset == 0 {
    75  		return nil
    76  	}
    77  	return a.buf[offset : offset+size : offset+size]
    78  }
    79  
    80  func (a *Arena) getPointer(offset uint32) unsafe.Pointer {
    81  	if offset == 0 {
    82  		return nil
    83  	}
    84  	return unsafe.Pointer(&a.buf[offset])
    85  }
    86  
    87  func (a *Arena) getPointerOffset(ptr unsafe.Pointer) uint32 {
    88  	if ptr == nil {
    89  		return 0
    90  	}
    91  	return uint32(uintptr(ptr) - uintptr(unsafe.Pointer(&a.buf[0])))
    92  }