Coroutines vs. Threads

If you’re familiar with working with multithreaded programs, then you may have come across the terms coroutine and thread. You may wonder what the difference between these two types of processes is and when to use one over the other. In this article, we’ll dive into the details of coroutines and threads to help you make better decisions when working with multithreaded programs in Python.

What are Coroutines?

A coroutine is a programming construct that enables suspending and resuming the execution of a function. A coroutine is similar to a thread except that it does not require any operating system level support. Instead, it uses the underlying hardware capabilities of the processor to suspend and resume its execution.

Implementing Coroutines

When implementing coroutines, there are a few key things to remember. First, coroutines must be cooperative; that is, they must yield control back to the caller when they are finished executing. Second, coroutines must be lightweight; they should not consume too much memory or CPU time.

Finally, coroutines should be asynchronous; they should not block or wait for other coroutines to finish executing.

How do coroutines work?

Coroutines use a combination of hardware and software mechanisms to suspend and resume their execution. When a coroutine is suspended, it saves its current state (e.g., registers) and context (e.g., stack). Then, when the coroutine is later resumed, it restores its saved state and context before continuing execution where it left off.

Coroutine Usage

1. Cooperative Tasking

Cooperative tasking is a technique that allows two or more threads to execute concurrently. To achieve this, each thread executes independently until they encounter a point at which they must cooperate. At this point, they synchronize their activities and exchange data.

2. Exception Handling

Exception handling is a mechanism that allows programmers to handle exceptional situations. An example of an exceptional situation is division by zero. The programmer would write code to detect if the operation resulted in a divide by zero error to handle this situation. If this happens, the programmer will take appropriate action.

3. Event Loops

An event loop is a mechanism that allows a program to react to events. For instance, a web browser may have an event loop that listens for HTTP requests. Whenever a request comes in, the event loop processes the request. Once the request is processed, the event loop goes back to listening for further incoming requests.


  1. Coroutines are cheaper than threads. They require less memory and resources so that they can save you money.
  2. Coroutines are more efficient. They take up less space and can be scheduled more efficiently, so your program will run faster.
  3. Coroutines are more flexible. You can easily change the order they execute or even cancel them entirely if you need to. This flexibility can make your code more straightforward to understand.


There are a few disadvantages of coroutines to be aware of. First, they can be difficult to debug because of their asynchronous nature. Second, they can lead to race conditions if not used carefully. Third, they can be CPU-intensive if used excessively. Fourth, they can cause memory leaks if not appropriately managed. Finally, they can be tricky to implement in some languages.

What are Threads?

A thread is not a process. A process is a sequence of execution steps performed by a single operating system instance. In contrast, threads share memory space and run concurrently (simultaneously) on a processor.

  1. Threads are not programs. A program is a collection of statements written in a language that instructs the computer on how to execute those statements.
  2. Threads are not objects. An object is a data structure containing information about something else. Objects are created using the keyword new and then assigned values.
  3. Threads are not variables. Variables store data.
  4. Threads are not classes. Classes define the structure of an object.
  5. Threads are not methods. Methods are actions that a class performs.
  6. Threads are not a subroutine. Subroutines are blocks of code that are called by a method.


1. Concurrency

Threads provide concurrency within a process, which means they can execute simultaneously without interfering with each other. In contrast, processes are sequential; they cannot run concurrently.

2. Communication

Threads communicate using shared memory. A thread communicates with another thread using a shared variable. Shared variables are stored in the same location in memory. If two threads want to access the same variable, then both threads need to read and write to the same location in memory, which is called synchronization. Synchronization is costly in terms of performance.

3. Economical

Creating and context switching threads is more economical than creating and context switching processes. Creating and context switching threads is less expensive than creating and context switching.


  1. They’re complicated. Threads require a lot of overhead, making your code more difficult to read and maintain.
  2. They’re inefficient. Context switching between threads is expensive and can lead to performance bottlenecks.
  3. They’re error-prone. It’s easy to introduce race conditions and other subtle bugs when working with threads.
  4. They don’t scale well.

Difference Between Coroutines vs. Threads

In computer programming, a coroutine is a subroutine that can suspend its execution at specific points, to be resumed later from the same point. This allows multiple subroutines to run concurrently within a single program. In contrast, a thread is a sequence of instructions within a program that can be executed independently of other code.

Code Example

In computer programming, a coroutine is a subroutine that can suspend its execution at any given point, to be resumed later from the same point. This allows multiple subroutines to run concurrently within a single program. A thread of execution (a thread) refers to a sequence of instructions executed by one or more CPUs.

Coroutines were added to Python 3 as an experimental feature, and they are not available in other languages such as C#, so threading is the only way for these languages. The best way to make sure you are writing multi-threaded code properly is with experience and by reading the documentation on how threads work in your language of choice.

User Guide

If you’re new to programming, you might wonder what the difference is between coroutines and threads. Both are ways to achieve concurrency, but they differ in how they work.

Use Cases

Regarding concurrency, there are two main approaches: coroutines and threads. Both have advantages and disadvantages, so it’s essential to understand their differences.


In conclusion, coroutines are a great way to improve your code’s readability and maintainability while still getting all the benefits of multithreading. If you’re not using coroutines in your code, you should consider doing so!