Исходники и презентации

lessons/allocator/stack_allocator/main.go

@@ -0,0 +1,100 @@
+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)
+}