> For the complete documentation index, see [llms.txt](https://ineelhere.gitbook.io/code-with-go/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ineelhere.gitbook.io/code-with-go/38-wait-groups.md).

# 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:

```go
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'.