Golang

Intro
Golang är det nya hippa språket som Google har utvecklat. Det är enkelt att läsa som Python, snabbt och low level som C.

Golang Concurreny

So basically goroutines are amazing in go, they are cheap, fast and even though one might think they run in parallel they don't. So lets say that I wanna run 2k HTTP GET requests towards skooog.se. Well I can do this concurrent, but we are gonna run into several issues, one being the amount of sockets we have on our client machine.

So sockets are expensive, goroutines aren't, this is how we solve it.

package main                                                                    
                                                                                
import (                                                                        
   "fmt"                                                                        
   "io/ioutil"                                                                  
   "net/http"                                                                   
   "sync"                                                                       
)                                                                               
                                                                                
// We need something to recover in case one goroutine fails.                    
// Otherwise our whole program might crash or hang                              
                                                                                
func cleanup() {                                                                
   if r := recover(); r != nil {                                                
       fmt.Println("recovered in cleanup", r)                                   
   }                                                                            
}                                                                               
                                                                                
func getURL(c chan<- *http.Response, wg *sync.WaitGroup, sem chan bool, url string) {
   defer wg.Done()                                                              
   defer cleanup()                                                              
   sem <- true                                                                  
   data, err := http.Get(url)                                                   
   if err != nil {                                                              
       panic(err)                                                               
   }                                                                            
                                                                                                                                                       
   c <- data                                                                    
   <-sem                                                                        
                                                                                
   // Tell the waitgroup we are done                                            
}                                                                               
                                                                                
func main() {                                                                   
   // Declare waitgroup                                                         
   var wg sync.WaitGroup                                                        
                                                                                
   // Make channels with buffersize to fit all our data
   c := make(chan *http.Response, 1000)                                         
                                                                                
   /*                                                                           
    We create sem to act as a buffer, because goroutines are cheap and we can use a lot, however
    sockets aren't. So we can easily spin up 10000 of goroutines without any issues,
    but then we will start running out of sockets to use.
   */                                                                           
   sem := make(chan bool, 50)                                                   
   for i := 0; i < 1000; i++ {                                                  
       // Add 1 to the queue                                                    
       wg.Add(1)                                                                
       go getURL(c, &wg, sem, "http://skooog.se")                               
   }                                                                            
   // Wait until every job we added is done                                     
   wg.Wait()                                                                    
                                                                                
   // Close channel is needed for when we use the range statement below         
   // If we don't close it range will never know when it should stop iterating, 
   // this will cause the problem to hang                                       
   close(c)                                                                     
   fmt.Println("ok")                                                            
                                                                                
   httpResponses := [][]byte{}                                                  
                                                                                
   for elem := range c {                                                        
       content, _ := ioutil.ReadAll(elem.Body)                                  
       //fmt.Println(string(content))                                           
       httpResponses = append(httpResponses, content)                           
   }                                                                            
                                                                                
   for _, slice := range httpResponses {                                        
       fmt.Println(string(slice))                                               
   }                                                                            
}