Table of Contents
Introduction
Welcome to this tutorial on understanding how Goroutines work in Go programming language. Goroutines are an essential part of Go’s concurrency model, allowing developers to write concurrent programs in an easy and efficient manner. In this tutorial, we will dive deep into Goroutines and explore the inner workings of the Go Scheduler.
By the end of this tutorial, you will have a solid understanding of Goroutines, how they are scheduled by the Go Scheduler, and how to effectively utilize them in your Go programs.
Prerequisites
Before starting with this tutorial, you should have a basic understanding of the Go programming language and its syntax. Familiarity with concepts like functions, variables, and control flow in Go will be helpful. You should also have Go installed on your system. If you haven’t installed Go yet, you can follow the official installation instructions available at the Go Website.
Goroutines
Goroutines are lightweight, independently executing functions that allow concurrent execution in Go programs. They enable you to write concurrent code that can perform tasks concurrently without the complexities of traditional thread-based programming.
Creating a Goroutine is as simple as prefixing a function call with the keyword go. Let’s consider an example:
package main
import (
"fmt"
"time"
)
func main() {
go sayHello()
go sayWorld()
time.Sleep(2 * time.Second) // Wait for Goroutines to finish
}
func sayHello() {
fmt.Println("Hello")
}
func sayWorld() {
fmt.Println("World")
}
In this example, we have two Goroutines sayHello and sayWorld, which are executed concurrently. The time.Sleep() function is used to wait for the Goroutines to finish execution before the program exits.
Goroutines are fast and lightweight due to their managed nature by the Go Scheduler.
The Go Scheduler
The Go Scheduler plays a crucial role in managing Goroutines and scheduling their execution on available threads. It is responsible for distributing Goroutines across hardware threads (typically CPU cores) and allowing them to execute independently and concurrently.
The Go Scheduler uses a technique called “work-stealing” to efficiently distribute and load balance Goroutines. It assigns Goroutines to worker threads and moves them between threads if necessary to achieve optimal utilization of system resources.
The following diagram illustrates the basic flow of work in the Go Scheduler:
+--------------+
| Main Goroutine |
+--------------+
|
V
+----------------+
| Goroutine Queue |<--------------------+
+----------------+ |
| |
V |
+-----------------+ |
| Running Goroutines | |
+-----------------+ |
| |
V |
+-----------------+ Goroutine Ready |
| Worker Pools | <---------+ |
+-----------------+ | |
| | |
V | |
+-----------------+ | |
| OS Threads 1 | | |
+-----------------+ | |
| | |
V | |
+-----------------+ | |
| OS Threads 2 | | |
+-----------------+ | |
| | |
V | |
+-----------------+ | |
| OS Threads 3 | | |
+-----------------+ | |
| | |
V | |
. <---------+ |
. Scheduler |
. |
| |
V |
+--------+--------+ |
| Operating | |
| System | |
+------------------+
Let’s go through the workflow:
- The main Goroutine is responsible for creating and starting other Goroutines.
- Goroutines are put into a Goroutine Queue.
- The Goroutine Scheduler takes Goroutines from the queue and puts them into worker pools.
- Worker pools consist of a set of OS threads that execute Goroutines concurrently.
- The Go Scheduler uses work-stealing to dynamically distribute Goroutines between the worker pools.
- Each OS thread executes the Goroutines assigned to it.
-
The OS threads interact with the operating system and execute Goroutines concurrently on different system threads.
-
The operating system manages and schedules the execution of system threads.
This parallel execution of Goroutines allows efficient utilization of CPU resources and provides excellent concurrency without the overheads of traditional threading models.
Goroutine Scheduling
The Go Scheduler uses a technique called “preemptive scheduling” to ensure fairness and prevent any single Goroutine from hogging system resources. It preemptively stops the execution of a Goroutine after a certain time slice (approximately a few microseconds) to give other Goroutines opportunities to run. This ensures that no Goroutine can monopolize the execution indefinitely.
The Scheduler also handles synchronization primitives like channels and locks. When a Goroutine blocks on a channel or a lock, it is removed from the running Goroutine set and put back into the Goroutine queue, allowing other Goroutines to progress and get scheduled. Once the channel or lock operation unblocks, the Goroutine is again made runnable and scheduled by the Scheduler.
Concurrency vs. Parallelism
It’s essential to understand the difference between concurrency and parallelism in the context of Goroutines and the Go Scheduler.
Concurrency is the ability of a program to deal with multiple tasks simultaneously. It doesn’t necessarily mean that the tasks are executing at the same time, but rather that they can make progress independently.
Parallelism, on the other hand, involves executing multiple tasks simultaneously on separate physical processors (CPU cores) to achieve speedup.
Go’s Goroutines and the Go Scheduler enable concurrency by allowing multiple Goroutines to run independently. The Scheduler handles scheduling and execution, making efficient use of available CPU resources.
However, parallelism is achieved when multiple Goroutines execute concurrently on different CPU cores. This is facilitated by the Go Scheduler, which distributes the Goroutines across available CPU cores.
By utilizing Goroutines, Go programmers can write concurrent code easily, and the Go Scheduler takes care of making effective use of the underlying hardware resources.
Conclusion
In this tutorial, we explored the concept of Goroutines and how they are scheduled by the Go Scheduler. We saw how Goroutines enable concurrent programming in an efficient and straightforward manner. The work-stealing mechanism of the Go Scheduler ensures optimal utilization of system resources.
Understanding the Go Scheduler is crucial for writing efficient concurrent programs in Go. By leveraging Goroutines and the Go Scheduler, developers can build scalable and high-performance applications.
Take some time to experiment with Goroutines and explore the behavior of the Go Scheduler further. It is a powerful tool that will enable you to write concurrent Go programs effectively.
Now that you have a good understanding of Goroutines and the Go Scheduler, you are well-equipped to write concurrent Go code and explore the world of Go’s concurrency model.
Happy coding!