Exploring the Use of Thread in Kotlin

1 – Introduction

Although Kotlin introduced coroutines as a more modern and efficient way to handle asynchronous tasks, Java's Thread class can still be used directly in Kotlin . This is useful for those who need more explicit control or are working on projects that use legacy Java libraries.

In this article, we will explore how to use the Thread class in Kotlin and when it might be a valid (albeit rare) choice.

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2 – What is a Thread?

A Thread is the smallest unit of execution managed by the operating system. In Kotlin (or Java), you can manually create threads to execute tasks in parallel.

Common problems with Thread:

• High creation and management cost: Threads consume significant system resources.
• Synchronization complexity: Controlling multiple threads manually can lead to bugs such as deadlocks.
• Blocking: Operations like Thread.sleep block the actual thread.

Despite these limitations, threads are still useful in scenarios where we need direct control.

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3 – How to Use Thread in Kotlin

The Thread class can be used in Kotlin in the same way as in Java. Let's start with a basic example.

Example 1: Creating a Thread in Kotlin

fun main() {
    val thread = Thread {
        println ("Running in Thread:${ Thread.currentThread().name}")
        Thread.sleep (1000) // Simulates a long task (1 second).
        println ( "Thread terminated.")
}

    thread.start() // Starts thread execution
    println ("Main thread:${Thread.currentThread().name}")
}

Expected console output:

Main thread: main
Running in Thread: Thread-0
Thread finished .

Explanation:

• Thread {...}: Creates a new thread and defines the code that will be executed.
• Thread.sleep: Simulates a pause (block) of 1 second.
• thread.start(): Starts the thread execution in parallel.

4 – Useful Methods of the Thread Class

4.1 – start:
Starts the execution of thread . The code inside the block will be executed in a separate thread .

4.2 – join:
Makes the main thread wait for another thread to complete.

Example:

fun main() {
    val thread = Thread {
        println("Thread starting ...")
        Thread.sleep(2000)
        println("Thread terminated.")
}

    thread.start()
    println("Waiting for Thread to finish...")
    thread.join() // Waits for the thread to finish before continuing.
    println("Thread completed, returning to main.")
}

Expected output:

Thread starting...
Waiting for the Thread to finish...
Thread finished.
Thread completed, returning to main.

4.3 – sleep :
Makes the current thread "sleep" for a specified period, blocking its execution.

Example:

fun main() {
    println("Main thread:${Thread.currentThread().name}")
    Thread.sleep(2000) // Pause for 2 seconds
    println("Main thread woke up.")
}

Warning: Using Thread.sleep should be avoided when possible, as it blocks the execution of the real thread .

5 – When to Use Thread in Kotlin ?
Although Kotlin offers coroutines as a more efficient solution for multitasking, the use of threads may still be necessary in some cases, such as:

1. Integration with legacy code: Old Java libraries that rely on explicit threads.
2. Low-level tasks: When you need full control over the execution and resources of the operating system.
3. Simple applications: Scenarios where the complexity of coroutines is not necessary.

6 – Comparison: Thread vs. Coroutines

Appearance	Thread	Coroutines
Management	Operating System	Kotlin
Creation cost	High	Low
Scalability	Limited	Highly scalable
Blocking	Yes, it can block threads.	No, it uses suspension.

7 – Conclusion

Using threads in Kotlin is perfectly possible, but should be done with caution. While threads are useful for specific scenarios, such as integration with legacy libraries or low-level tasks, Kotlin coroutines are generally the best choice for most projects.

In the next article, we will continue exploring how to use coroutines to optimize your applications in an efficient and modern way.

Reference
Official Kotlin documentation on coroutines