In-depth analysis of Golang slicing principle: memory allocation and expansion strategy

Introduction:
Slicing is one of the commonly used data types in Golang, which provides convenient way to operate on continuous data sequences. When using slices, it is important to understand its internal memory allocation and expansion strategies to improve program performance. In this article, we will provide an in-depth analysis of the principles of Golang slicing, accompanied by specific code examples.

1. The memory structure and basic principles of slicing
In Golang, a slice is a reference type to the underlying array and does not directly hold any data itself. The memory structure of a slice mainly consists of three parts: a pointer to the underlying array, the length of the slice, and the capacity of the slice. Among them, the length of the slice refers to the number of current elements in the slice, and the capacity of the slice refers to the number from the starting position of the slice to the last element of the underlying array.

When we create a slice through the make function, Golang will allocate a contiguous memory block in memory as the underlying array and return a pointer to this memory block. At the same time, a slice object is also created, which contains a pointer to the underlying array, the length of the slice, and the capacity of the slice. This way, we can access and manipulate the underlying array through the slice object.

2. Memory allocation strategy of slices
When we append elements to a slice, if the capacity of the underlying array is not enough to accommodate the new elements, Golang will reallocate the memory through the memory allocation strategy. , and copies the original elements to the new memory space.

Golang's memory allocation strategy adopts an exponential growth method, that is, when the capacity of the underlying array is insufficient, it will be expanded by 2 times the original capacity. Specifically, when the capacity of the underlying array is less than 1024, the expansion will be performed at 2 times the capacity; when the capacity of the underlying array is greater than or equal to 1024, the expansion will be performed at 1.25 times the capacity. The design of this strategy can not only effectively reduce memory waste, but also improve program performance.

3. Code example of slice expansion process
Below, we will demonstrate the slice expansion process through a specific code example. Suppose we have a slice with an initial capacity of 4 and we want to append elements to it.

package main

import "fmt"

func main() {
    s := make([]int, 0, 4)
    fmt.Printf("初始切片的長(zhǎng)度：%d，容量：%d
", len(s), cap(s))

    for i := 0; i < 10; i++ {
        s = append(s, i)
        fmt.Printf("追加第%d個(gè)元素后，切片的長(zhǎng)度：%d，容量：%d
", i+1, len(s), cap(s))
    }
}

The output results are as follows:

初始切片的長(zhǎng)度：0，容量：4
追加第1個(gè)元素后，切片的長(zhǎng)度：1，容量：4
追加第2個(gè)元素后，切片的長(zhǎng)度：2，容量：4
追加第3個(gè)元素后，切片的長(zhǎng)度：3，容量：4
追加第4個(gè)元素后，切片的長(zhǎng)度：4，容量：4
追加第5個(gè)元素后，切片的長(zhǎng)度：5，容量：8
追加第6個(gè)元素后，切片的長(zhǎng)度：6，容量：8
追加第7個(gè)元素后，切片的長(zhǎng)度：7，容量：8
追加第8個(gè)元素后，切片的長(zhǎng)度：8，容量：8
追加第9個(gè)元素后，切片的長(zhǎng)度：9，容量：16
追加第10個(gè)元素后，切片的長(zhǎng)度：10，容量：16

As can be seen from the output results, in the initial state, the capacity of the slice is 4. When the fourth element is appended, the capacity of the slice is not enough to accommodate the new element. At this time, Golang will reallocate the memory and expand the capacity of the underlying array to 8. Similarly, when the ninth element is appended, the capacity of the underlying array is insufficient again, and the capacity is expanded to 16. This exponentially increasing memory allocation strategy can improve program performance in most cases.

Conclusion:
Through an in-depth analysis of Golang slices, we understand that slices are a reference type to the underlying array, and their internal memory allocation and expansion strategies are very important. Golang's slicing uses an exponential growth method to allocate memory. This strategy can effectively reduce memory waste and improve program performance. In actual programming, we should make reasonable use of the characteristics of slices and pay attention to the impact of memory allocation and expansion to optimize and improve program efficiency.

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