101 lines
2.0 KiB
Go
101 lines
2.0 KiB
Go
|
package main
|
||
|
|
|
||
|
|
import (
|
||
|
|
"errors"
|
||
|
|
"fmt"
|
||
|
|
"math"
|
||
|
|
"unsafe"
|
||
|
|
)
|
||
|
|
|
||
|
|
const headerSize = 2
|
||
|
|
|
||
|
|
type StackAllocator struct {
|
||
|
|
data []byte
|
||
|
|
}
|
||
|
|
|
||
|
|
func NewStackAllocator(capacity int) (StackAllocator, error) {
|
||
|
|
if capacity <= 0 {
|
||
|
|
return StackAllocator{}, errors.New("incorrect capacity")
|
||
|
|
}
|
||
|
|
|
||
|
|
return StackAllocator{
|
||
|
|
data: make([]byte, 0, capacity),
|
||
|
|
}, nil
|
||
|
|
}
|
||
|
|
|
||
|
|
func (a *StackAllocator) Allocate(size int) (unsafe.Pointer, error) {
|
||
|
|
if size > math.MaxInt16 {
|
||
|
|
// can increase header size
|
||
|
|
return nil, errors.New("incorrect size")
|
||
|
|
}
|
||
|
|
|
||
|
|
previousLength := len(a.data)
|
||
|
|
newLength := previousLength + headerSize + size
|
||
|
|
|
||
|
|
if newLength > cap(a.data) {
|
||
|
|
// can increase capacity
|
||
|
|
return nil, errors.New("not enough memory")
|
||
|
|
}
|
||
|
|
|
||
|
|
a.data = a.data[:newLength]
|
||
|
|
header := unsafe.Pointer(&a.data[previousLength])
|
||
|
|
pointer := unsafe.Pointer(&a.data[previousLength+headerSize])
|
||
|
|
|
||
|
|
*(*int16)(header) = int16(size)
|
||
|
|
return pointer, nil
|
||
|
|
}
|
||
|
|
|
||
|
|
func (a *StackAllocator) Deallocate(pointer unsafe.Pointer) error {
|
||
|
|
// can deallocate without pointer
|
||
|
|
if pointer == nil {
|
||
|
|
return errors.New("incorrect pointer")
|
||
|
|
}
|
||
|
|
|
||
|
|
header := unsafe.Add(pointer, -headerSize)
|
||
|
|
size := *(*int16)(header)
|
||
|
|
|
||
|
|
previousLength := len(a.data)
|
||
|
|
newLength := previousLength - headerSize - int(size)
|
||
|
|
|
||
|
|
a.data = a.data[:newLength]
|
||
|
|
return nil
|
||
|
|
}
|
||
|
|
|
||
|
|
func (a *StackAllocator) Free() {
|
||
|
|
a.data = a.data[:0]
|
||
|
|
}
|
||
|
|
|
||
|
|
func store[T any](pointer unsafe.Pointer, value T) {
|
||
|
|
*(*T)(pointer) = value
|
||
|
|
}
|
||
|
|
|
||
|
|
func load[T any](pointer unsafe.Pointer) T {
|
||
|
|
return *(*T)(pointer)
|
||
|
|
}
|
||
|
|
|
||
|
|
func main() {
|
||
|
|
const KB = 1 << 10
|
||
|
|
allocator, err := NewStackAllocator(KB)
|
||
|
|
if err != nil {
|
||
|
|
// handling...
|
||
|
|
}
|
||
|
|
|
||
|
|
defer allocator.Free()
|
||
|
|
|
||
|
|
pointer1, _ := allocator.Allocate(2)
|
||
|
|
defer allocator.Deallocate(pointer1)
|
||
|
|
pointer2, _ := allocator.Allocate(4)
|
||
|
|
defer allocator.Deallocate(pointer2)
|
||
|
|
|
||
|
|
store[int16](pointer1, 100)
|
||
|
|
store[int32](pointer2, 200)
|
||
|
|
|
||
|
|
value1 := load[int16](pointer1)
|
||
|
|
value2 := load[int32](pointer2)
|
||
|
|
fmt.Println("value1:", value1)
|
||
|
|
fmt.Println("value2:", value2)
|
||
|
|
|
||
|
|
fmt.Println("address1:", pointer1)
|
||
|
|
fmt.Println("address2:", pointer2)
|
||
|
|
}
|