How does golang function wait for goroutine to complete through WaitGroup?

WaitGroup is a synchronization mechanism in Go for coordinating goroutine execution. Use this to ensure that the main goroutine waits for a group of goroutines to complete before continuing execution. Specific usage: Create a WaitGroup instance and set an initial counter for it, indicating the number of goroutines to wait for. For each goroutine to wait on, call wg.Add(1) to increment the counter. After the goroutine completes, call wg.Done() to decrement the counter. Finally, the main goroutine calls wg.Wait() to block itself until all goroutines have completed.

How to use WaitGroup to wait for Goroutine to complete in Go

WaitGroup in Go is a kind of synchronization Mechanism for coordinating the execution of multiple goroutines. It allows the main goroutine to wait for a group of goroutines to complete, thereby ensuring that all related tasks have completed before continuing execution.

Usage:

Create a WaitGroup instance and set an initial counter for it, indicating the number of goroutines to wait for. For each goroutine to wait on, call wg.Add(1) to increment the counter, and after the goroutine completes, call wg.Done() to decrement the counter. Finally, the main goroutine calls wg.Wait() to block itself until all goroutines have completed.

Code sample:

package main

import (
    "fmt"
    "sync"
)

var wg sync.WaitGroup

func main() {
    // 创建一个需要等待 3 个 goroutine 完成的 WaitGroup
    wg.Add(3)

    // 创建 3 个 goroutine
    for i := 0; i < 3; i++ {
        go func(i int) {
            fmt.Printf("Goroutine %d started\n", i)
            
            // 模拟一些需要时间的工作
            for j := 0; j < 10000; j++ {}
            
            fmt.Printf("Goroutine %d finished\n", i)
            
            // 通知 WaitGroup 该 goroutine 已完成
            wg.Done()
        }(i)
    }

    // 等待所有 goroutine 完成
    wg.Wait()
    fmt.Println("All goroutines have finished")
}

Practical case:

This code sample simulates a simple Web server that Multiple goroutines will be started to handle requests. To ensure that the goroutine has completed before shutting down the server, we use WaitGroup to wait for all goroutines to complete.

package main

import (
    "fmt"
    "net/http"
    "sync"
)

var wg sync.WaitGroup

func main() {
    // 创建一个需要等待所有 HTTP 请求完成的 WaitGroup
    wg.Add(10)

    // 监听端口 8080
    http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
        fmt.Fprintf(w, "Hello, World!")
        
        // 请求处理完毕后，通知 WaitGroup
        wg.Done()
    })
    http.ListenAndServe(":8080", nil)
    
    // 等待所有 HTTP 请求完成
    wg.Wait()
    fmt.Println("All HTTP requests have been processed")
}

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