How to Safely Create a Go Slice from an Array Pointer Without Memory Copying?

Creating an Array or Slice from an Array Pointer in Golang

In Golang, creating an array or slice from an array pointer using unsafe.Pointer can be challenging due to the memory copy incurred by traditional methods like memcpy or reflect.SliceHeader. To address this issue, we discuss alternative approaches.

Foreword:

Before delving into the solutions, it's crucial to note that using uintptr values does not prevent the original array from being garbage collected. Hence, it's essential to exercise caution when handling such values, ensuring their validity before accessing them. Additionally, it's highly recommended to limit usage of the unsafe package, prioritizing Go's type safety mechanisms.

Solution Using reflect.SliceHeader:

One effective method involves manipulating the reflect.SliceHeader descriptor of a slice variable to point to the desired array. This involves modifying its Data, Len, and Cap fields.

var data []byte

sh := (*reflect.SliceHeader)(unsafe.Pointer(&data))
sh.Data = p // Pointer to the array
sh.Len = size
sh.Cap = size

fmt.Println(data)

By performing these modifications, the data slice variable effectively points to the same array as the initial pointer.

Alternative Solution Using Composite Literal:

Another approach is to create a reflect.SliceHeader using a composite literal, then convert it to a slice:

sh := &reflect.SliceHeader{
    Data: p,
    Len:  size,
    Cap:  size,
}

data := *(*[]byte)(unsafe.Pointer(sh))

fmt.Println(data)

This method produces the same result as the previous solution.

Caveats and Warnings:

The aforementioned solutions rely on the assumption that the original array will not be garbage collected while the pointer is being used. It is crucial to ensure that the supplier of the pointer guarantees its validity.

Additionally, the documentation for unsafe.Pointer explicitly warns against declaring or allocating variables of the reflect.SliceHeader struct type directly. Instead, they should only be used as pointers pointing to actual slices or strings.

The above is the detailed content of How to Safely Create a Go Slice from an Array Pointer Without Memory Copying?. For more information, please follow other related articles on the PHP Chinese website!