What is Concurrency?

Concurrency is when code is running in parallel or alongside a parent program using another CPU core. Concurrency allows to break up a program to be executed out-of-order at the same time.

What is Concurrency used for?

Concurrency is used such as separating an API call to the server this allows for the server to still accept requests and handle multiple at the same time. Concurrency can also be used for simultaneous processes to run at the same time or splitting up CPU intensive work.

Concurrency in Golang

Goroutines

A goroutine is a concurrent process in Golang running separate to the main thread. Lets start with a simple concurrent program.

package main

import (
 "fmt"
 "time"
)

func main() {
 count("task 1")
 count("task 2")
}

func count(thing string) {
 for i := 1; i <= 5; i++ {
        fmt.Println(thing)
        time.Sleep(time.Second * 2)
    }
}

In this program we have 2 tasks both running in the main function. They both will print their text every two seconds 5 times. But in this program there is no concurrency so the first task will execute first then the second. If we make the first task a goroutine it will run in parallel. We add the "go" in front of the function to run it concurrently.

Golang handles the process of interacting with the CPU to run it separately which gives us the easy job.

func main() {
 go count("task 1")
 count("task 2")
}

The two tasks now run in parallel and the program exits when they are finished. If we were to run both functions concurrently they would exit immediately because the main thread finished.

Conclusion

Concurrency is great and has many uses but keep in mind just adding hundreds of go routines isn't going to make your program run faster as it is ultimately determined by the CPU.