substack-concurrency-12.go

var numCalcsCreated int
calclPool := &sync.Pool{
    New: func() interface{}{
        numCalcsCreated += 1
        mem := make([]byte, 1024)
        return &mem
    },
}

// Seed the pool with 4KB
calclPool.Put(calclPool.New())
calclPool.Put(calclPool.New())
calclPool.Put(calclPool.New())
calclPool.Put(calclPool.New())

const numWorkers = 1024*1024
var wg sync.WaitGroup
wg.Add(numWorkers)

for i:=numWorkers; i>0; i-- {
    go func() {
        defer wg.Done()
        
        mem := calcPool.Get().(*[]byte)
        defer calcPool.Put(mem)
    }()
}

wg.Wait()
fmt.Printf(numCalcsCreated) // 8