In-depth exploration: The principle and internal implementation of Go WaitGroup

In-depth exploration: The principle and internal implementation of Go WaitGroup

The concurrency model of the Go language is one of its distinctive features. In Go language, we can use goroutine and channel to implement lightweight concurrent operations. However, in some cases, we need to wait for all goroutines to complete before proceeding to the next step. At this time, you need to use WaitGroup.

WaitGroup is a concurrency primitive in the Go language, which can be used to wait for the execution of goroutine to complete. This article will deeply explore the principles and internal implementation of WaitGroup, and give specific code examples.

Principle of WaitGroup:
WaitGroup is similar in function to a counter. It can be used to track the execution of a group of goroutines. Specifically, WaitGroup manages the number of goroutines through a counter. When we create a WaitGroup, the initial value of the counter is 0. At the beginning of each goroutine, we can call the Add method of WaitGroup to increment the counter value. At the end of the goroutine, we can call the Done method of WaitGroup to decrement the counter value. When the value of the counter becomes 0, it means that all waiting goroutines have been executed, the Wait method will return, and the program continues to perform the next step.

Internal implementation of WaitGroup:
The internal implementation of WaitGroup is relatively complex. It mainly relies on mutex locks and condition variables to achieve concurrency safety. Specifically, WaitGroup contains three fields: a mutex (mutex), a condition variable (cond), and a counter (counter).

Mutex lock (mutex) is used to protect the increase and decrease operations of the counter and the access of waiting threads. Mutex is a common concurrency control mechanism that ensures that only one goroutine can access shared resources at the same time.

Condition variable (cond) is used to implement waiting and notification functions. When the counter reaches 0, all waiting threads will be awakened. In this way, we can use condition variables to implement the blocking and wake-up operations of the Wait method.

The counter records the number of waiting goroutines. When each goroutine starts executing, the counter value is automatically increased by 1. When the goroutine ends execution, the counter value will automatically be decremented by 1. When the value of the counter becomes 0, it means that all waiting goroutines have been executed.

Here is a sample code that shows how to use WaitGroup:

package main

import (
    "fmt"
    "sync"
)

func main() {
    var wg sync.WaitGroup

    for i := 0; i < 5; i++ {
        wg.Add(1)
        go func(i int) {
            defer wg.Done()
            fmt.Printf("goroutine %d
", i)
        }(i)
    }

    wg.Wait()
    fmt.Println("All goroutines have finished")
}

In the above code, we create a WaitGroup and call the Add method at the beginning of each goroutine. At the end of the goroutine, we use the defer keyword to call the Done method. Finally, we call the Wait method to block the main goroutine until all goroutines are executed.

Summary:
This article deeply explores the principles and internal implementation of WaitGroup in Go language, and gives specific code examples. By using WaitGroup, we can conveniently wait for the execution of a group of goroutines to complete. At the same time, understanding the principles and internal implementation of WaitGroup will also help us better understand and use the concurrency model of Go language.

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