golang atomic replacement

Golang is a programming language developed by Google. It has very powerful functions in concurrent programming. One of them is atomic operations, which ensure the correctness of shared resources in a multi-threaded environment. In Golang, atomic operations are provided by the sync/atomic package. This article will introduce the atomic replacement operation in detail.

Before introducing atomic substitution, let’s first understand what atomic operations are. In multi-threaded programming, if multiple threads need to access a shared resource at the same time, some problems will occur if the access is not coordinated. For example, if multiple threads try to modify the same value at the same time, a race condition may occur, causing program errors or unpredictable behavior.

To solve this problem, we can use a technique called atomic operations. An atomic operation is an indivisible operation that cannot be interrupted or modified during execution. This avoids race conditions caused by multiple threads accessing shared resources at the same time. Golang provides some atomic operation functions, such as AddInt32, AddInt64, CompareAndSwapInt32, etc.

The atomic replacement operation functions are SwapInt32, SwapInt64, SwapUint32, SwapUint64, and SwapPointer. Taking SwapInt32 as an example, its function prototype is as follows:

func SwapInt32(addr *int32, new int32) (old int32)

This function receives a pointer to an int32 type variable and a new The int32 value, it will try to replace the value at the memory address pointed by the pointer with the new value and return the original value. If the replacement fails due to concurrent modification, the original value is returned. This function is atomic, even if multiple threads call SwapInt32 at the same time to modify the same value, there will be no problem.

Let’s look at a simple example. The counter in the example is a variable of type int32, and multiple threads will try to increase its value by 1 at the same time. If you do not use atomic replacement operations, you need to use locks to ensure that multiple threads do not modify the counter at the same time, which will cause performance degradation. With atomic replacement operations, no locks are required. The code is as follows:

package main

import (
    "fmt"
    "sync/atomic"
    "time"
)

func main() {
    var counter int32
    
    for i := 1; i <= 10; i++ {
        go func() {
            for {
                oldValue := atomic.LoadInt32(&counter)
                if atomic.CompareAndSwapInt32(&counter, oldValue, oldValue+1) {
                    break
                }
                time.Sleep(time.Millisecond)
            }
        }()
    }
    
    time.Sleep(time.Second * 1)
    
    fmt.Println(counter)
}

In this example, we set the initial value of the counter to 0 and started 10 goroutines to add 1 to it. In each goroutine, we use a for loop to continuously try to increment the counter value by 1. The LoadInt32 function is used here to read the counter value, and the CompareAndSwapInt32 function is used to perform atomic replacement operations. Here oldValue is used as the base value for comparison. If the value of the current counter is the same as oldValue, an atomic replacement operation is performed. If the replacement succeeds, exit the loop; if the replacement fails, wait for a while and try again.

In this example, a possible race condition is that multiple goroutines read the value of counter as k at the same time, and then increase it by 1 at the same time, causing the counter to only increase by 1. However, due to the use of atomic replacement operations, each goroutine will only operate when it attempts to modify the counter. Other threads cannot modify the counter, so no race conditions will occur. The final counter value output by the program should be 10, and the result is generally like this.

This article introduces the atomic replacement operation functions in Golang, including SwapInt32, SwapInt64, SwapUint32, SwapUint64, and SwapPointer. Atomic operations are an important means to ensure the correctness of shared resources in multi-threaded programming, and they can avoid race conditions. Golang provides some atomic operation functions to implement functions such as spin locks and CAS operations. Programmers can choose appropriate atomic operation functions to solve problems in concurrent programming.

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