Tell me about the Semaphore pattern?

The Semaphore pattern is a synchronization mechanism that limits the number of operations executing simultaneously or access to a resource.

In Go, a semaphore can be implemented using a channel, limiting the number of goroutines that can execute a critical section at the same time.

Example of a simple semaphore in Go:

package main

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

func main() {
	sem := make(chan struct{}, 3) // semaphore with a capacity of 3
	var wg sync.WaitGroup

	for i := 0; i < 10; i++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			sem <- struct{}{} // acquire semaphore
			fmt.Printf("Goroutine %d started work\n", id)
			time.Sleep(1 * time.Second) // simulate work
			fmt.Printf("Goroutine %d finished work\n", id)
			<-sem // release semaphore
		}(i)
	}

	wg.Wait()
}

In this example, no more than three goroutines can work simultaneously. Semaphores are useful for limiting parallelism, for example, when working with limited resources (connections, files, etc.).