Threads vs. Coroutines: What's the Difference and Why Does It Matter?

1 – Introduction

Both threads and coroutines handle concurrent tasks, but in very different ways. To choose which approach to use, it's important to understand their differences and the impact they have on performance and code readability.

Threads are managed by the operating system, while coroutines are managed by Kotlin , offering greater control and efficiency. Throughout this article, we will explore these differences and show how coroutines solve the problems of traditional threads .

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2 – Technical Difference

Threads (Java):

• Managed by the operating system.
• High cost of creation and management.
• They work at the hardware level, operating directly on processing cores.
• Can lead to problems such as deadlocks and high memory consumption.

Coroutines (Kotlin):

• Managed by the Kotlin library .
• Much lighter and more efficient.
• They operate at a level of abstraction, allowing you to pause and resume tasks without blocking real threads.
• They facilitate writing concise and readable code.

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3 – Table Comparison

Aspect	Threads	Coroutines
Management	Operating System	Kotlin
Creation Cost	High	Low
Lifecycle Control	Difficult	Made easier by scopes
Blocking	Yes, it can block real threads.	No, it uses smart suspension.
Scalability	Limited by OS capacity.	Highly scalable

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4 – Practical Example

Let's see in practice how threads and coroutines differ.

Using Threads in Java:

public class Main {
    public static void main(String[] args) {
        Thread thread1 = new Thread(() -> {
            System.out.println("Thread 1 starting ...");
            try {
                Thread.sleep(2000); // Simulate long task .
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("Thread 1 finished .");
        });

        Thread thread2 = new Thread(() -> {
            System.out.println("Thread 2 starting ...");
            try {
                Thread.sleep(1000); // Simulate long task .
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("Thread 2 finished .");
        });

        thread1.start();
        thread2.start();
    }
}

Console output:

Thread 1 starting ...
Thread 2 starting ...
Thread 2 finished .
Thread 1 finished.

- Problem: Managing threads manually requires more code and attention to exceptions. Additionally, Thread.sleep blocks real threads .

Using Coroutines in Kotlin :

import kotlinx.coroutines .*

fun main() = runBlocking {
    val coroutine1 = launch {
        println("Coroutine 1 starting...")
        delay(2000) // Suspend without blocking.
        println("Coroutine 1 finished.")
    }

    val coroutine2 = launch {
        println("Coroutine 2 starting...")
        delay(1000) // Suspend without blocking.
        println("Coroutine 2 finished.")
    }

    coroutine1.join()
    coroutine2.join()
}

Console output:

Coroutine 1 starting...
Coroutine 2 starting...
Coroutine 2 completed.
Coroutine 1 completed.

• Benefit: Using delay suspends execution without blocking the thread, and management is simplified with launch.

5 – Conclusion

While threads are useful for multitasking, they have significant limitations, such as high creation costs and difficulty in managing them. Kotlin coroutines are a modern and efficient alternative, allowing you to write more readable and scalable code .

In the next article, we'll explore how Dispatchers and Contexts help control where and how coroutines run.

Reference
Official Kotlin documentation on coroutines