Go Concurrency 1.1 — Sync Package | WaitGroup & Mutex

Originally published at — https://amanreasoned.com

Memory access synchronisation is one of the popular ways to achieve concurrency in various languages. Sync package is one of the major difference between these languages and Go. The package provides you new set of concurrency primitives with wide abilities on top of the memory access synchronisation primitives. I am going to briefly talk about some of the commonly used tools from this package.

WaitGroup

It is an excellent abstraction to wait for a set of Go routines when you either don’t care about the result or have other ways to collect the result

package main  
  
import (  
   "fmt"  
   "sync"   
   "time")  
  
func main() {  
   maxConcurrency := 2  
   var wg sync.WaitGroup  
   for i := 0; i < maxConcurrency; i++{  
      wg.Add(1)  
      go func(wg *sync.WaitGroup, i int) {  
         defer wg.Done()  
         fmt.Printf("\n Go routine %d going to sleep", i)  
         time.Sleep(time.Second * 1)  
      }(&wg, i)  
   }  
  
   wg.Wait()  
   fmt.Printf("\nAll Go routines complete.")  
}

Go Playground

Application

To fire up multiple Go routines and wait for them to complete before moving forward.

• Firing of multiple queries part of a common result that needs to be returned.
• Firing of multiple HTTP request and waiting for them to complete.

Mutex

This tool helps guard a critical section in your program. A critical section is nothing but a part of your program that could be sharing access to a memory with another part of the program at the same time. Mutex stands for mutual exclusion. It a way to provide concurrent safe access to a shared resource.

package main  
  
import (  
   "fmt"  
   "sync")  
  
func main() {  
   var counter int  
   increment := func(wg *sync.WaitGroup, m sync.Locker) {  
      defer wg.Done()  
         m.Lock()  
         defer m.Unlock()  
         counter++  
         fmt.Printf("\nPost increment count %d", counter)  
   }  
  
   decrement := func(wg *sync.WaitGroup, m sync.Locker) {  
      defer wg.Done()  
         m.Lock()  
         defer m.Unlock()  
         counter--  
         fmt.Printf("\nPost decrement count %d", counter)  
   }  
  
   iterations := 5  
   var lock sync.Mutex  
   var wg sync.WaitGroup  
   for i:=0; i < iterations; i++{  
      wg.Add(1)  
      go increment(&wg, &lock)  
   }  
  
   for i:=0; i < iterations; i++{  
      wg.Add(1)  
      go decrement(&wg, &lock)  
   }  
   wg.Wait()  
   fmt.Println("\nOperation complete")  
}

Go Playground

Application

Any resource that is being modified/accessed by multiple Go routines.

• Appending errors from multiple queries together from a set of Go routines part of the current scope.
• Appending results together from a set of Go routines performing HTTP requests.