Wait Groups

This Go code demonstrates the use of the sync.WaitGroup to wait for a collection of goroutines to finish their execution. Let's go through it with inline comments:

package main

import (
    "fmt"
    "sync"
    "time"
)

// worker function represents a worker that performs some work
func worker(id int) {
    fmt.Printf("Worker %d starting\n", id)

    // Simulate work by sleeping for one second
    time.Sleep(time.Second)

    fmt.Printf("Worker %d done\n", id)
}

func main() {
    // Creating a WaitGroup to wait for all goroutines to finish
    var wg sync.WaitGroup

    for i := 1; i <= 5; i++ {
        // Incrementing the WaitGroup counter for each goroutine
        wg.Add(1)

        // Creating a local variable 'i' to capture the current value
        i := i

        // Launching a goroutine for each worker
        go func() {
            // Decrementing the WaitGroup counter when the goroutine completes
            defer wg.Done()
            worker(i)
        }()
    }

    // Waiting for all goroutines to finish
    wg.Wait()
}

Output

Worker 2 starting
Worker 3 starting
Worker 5 starting
Worker 4 starting
Worker 1 starting
Worker 1 done
Worker 4 done
Worker 5 done
Worker 2 done
Worker 3 done

Explanation:

1. package main: Indicates that this Go file belongs to the main executable package.

2. import (...): Imports necessary packages, including "fmt" for formatting and printing, "sync" for synchronization, and "time" for handling time-related operations.

3. func worker(id int) { ... }: Defines a worker function that simulates work by sleeping for one second and prints messages.

4. var wg sync.WaitGroup: Creates a sync.WaitGroup variable named 'wg' to wait for a collection of goroutines to finish.

5. wg.Add(1): Increments the WaitGroup counter for each goroutine to indicate that a new goroutine is starting.

6. i := i: Creates a local variable 'i' to capture the current value of the loop variable, preventing its value from changing in the closure.

7. go func() { ... }(): Launches a goroutine for each worker. The defer wg.Done() statement is used to decrement the WaitGroup counter when the goroutine completes.

8. wg.Wait(): Waits for all goroutines to finish by blocking until the WaitGroup counter becomes zero.

This code demonstrates how to use a sync.WaitGroup to coordinate the execution of multiple goroutines. Each worker is launched as a goroutine, and the WaitGroup is used to wait for all workers to complete their work before proceeding further in the main function. The use of a local variable inside the loop ensures that each goroutine captures the correct value of 'i'.