Go Concurrency 1.2 — Sync Package | Once & Pool

Originally published at — https://amanreasoned.com

Once

It is a type that internally utilises the sync primitives to ensure that only one call happens to the passed in function. Note — it does not care about the unique functions passed in, and only cares about the invocation on the sync.Once.Do(f func()) method.

package main

import (
 "fmt"
 "sync"
)
func main() {
 var counter int
 var once sync.Once
 for i := 0; i < 10; i++ {
  once.Do(func() {
   counter++
  })
  
 }
 fmt.Println(counter)
}

Playground

Application

• Any kind of initialisation logic, various clients like — DB clients, loggers etc

Pool

It is a type that allow concurrent safe way to create and re-use objects that could be costly to create or are being used by processes that dispose of these objects rapidly. The type has two main methods Get and Put. When the Get is called first it checks if there are any available instances in the pool else it calls the New member variable to issue a new one, once the resource has been used it can be freed up and be allocated back to the pool using the Put method.

package main  
  
import (  
   "fmt"  
   "sync")  
  
var instanceCount int  
  
func warmUpPool(p *sync.Pool, resourceCount int) {  
   for i := 0; i < resourceCount; i++ {  
      p.Put(p.New())  
   }  
}  
  
func main() {  
   p := sync.Pool{  
      New: func() interface{} {  
         fmt.Println("Creating new resource")  
         instanceCount++  
         s := make([]byte, 1024)  
  
         return s  
      },  
   }  
  
   warmUpPool(&p, 4)  
   var wg sync.WaitGroup  
   for i := 0; i < 100; i++ {  
      wg.Add(1)  
      go func() {  
         defer wg.Done()  
         resource := p.Get()  
         p.Put(resource)  
      }()  
   }  
  
   wg.Wait()  
   fmt.Println(instanceCount)  
}

Playground

Application

• Database pool to be leveraged by multiple workers at a time.
• Cache to be utilised by multiple workers.

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