In this post, we will be looking at goroutines in Go. Go is a language that was built with concurrency in mind. Given that almost all of the computers of the modern era employ the use of multiple cpu cores, this is a natural approach. Go makes use of a special feature called the Goroutine to handle concurrency. You can use these goroutines to call on lightweight threads to run a function. Before we take a look at examples, lets talk about concurrency for a moment.

Concurrency in Computing

Concurrency is the use of independent processes that work in an asynchronous order to complete a task. There are many examples of concurrency in the real world. We can look at how trains share tracks with one another, how in multiplayer games each player can make an action independent of one another, and how society in general works with each person making their own decisions. Naturally, many things use a model of concurrency.

Logically, it makes sense to apply this type of behavior to a computer program. When you download a file, listen to an audio stream, send a message over the web, print out a document, or even type in a text editor, you are making use of concurrency in programs. Some programming languages use different methods to handle concurrency and Go is certainly no exception with it’s goroutines. 


Examples of Goroutines in Go

The simple definition of a goroutine, is a function that is capable of running concurrently with other functions. To invoke a goroutine, we simply place the word go in front of a function execution call. Let us look at a very simple example of this.

In this example we use a for-loop to iterate through ten values (0 to 9) inside of our function. Our main function has its own thread and in a way, the main function itself runs like a goroutine. We invoke a second goroutine with our function by typing go a(0). If we were to remove the goroutine and the Scanln function call, the function would run normally and then the program would end after execution. However, because the function is running on a separate thread then the main function, if we were to remove the Scanln call and leave the goroutine, the program will terminate before the end of the function. This happens because the main function doesn’t wait for the goroutine to end before moving on to execute the rest of the code.gopher_pipe

Because goroutines are very lightweight threads, we can literally call on thousands of them in a piece of code (the average 64 bit cpu can use 100,000 goroutines at once). Let us look at an example that uses many goroutines.

In this example, we are assigning ten threads (labeled 0 to 9) to our function by using our for loop. In our function, we are iterating through ten values again, however, each time we are now stopping and waiting for a random period of time which is between 0 and 250 milliseconds before the thread continues execution. In this way, we can see the way the threads are actually running parallel and concurrent to one another. You will notice that threads that were deployed before others may end execution well after the others have finished.


In this post we looked at how we can spawn threads and run functions concurrently in Go. The talked about goroutines and gave a general overview of concurrency. In our next few posts we will talk about how we can send data from one goroutine to the other using channels.