Job lifecycle and cancellation in Kotlin - Mini Project: Build & Apply

Job lifecycle and cancellation

📖 Scenario: You are building a simple Kotlin program that uses coroutines to run a background task. You want to understand how to start a job, check its status, and cancel it properly.

🎯 Goal: Learn how to create a coroutine Job, check if it is active or completed, and cancel it safely.

📋 What You'll Learn

Create a coroutine Job that runs a simple repeating task

Add a variable to hold the Job

Use coroutine lifecycle properties like isActive and isCompleted

Cancel the Job and print its status

💡 Why This Matters

🌍 Real World

Understanding job lifecycle and cancellation is important when running background tasks in Android apps or server applications to avoid wasting resources.

💼 Career

Many Kotlin developer roles require knowledge of coroutine management to write efficient and responsive asynchronous code.

1

Create a coroutine Job with a repeating task

Write code to create a coroutine Job named job that runs a repeating task printing "Working..." every 300 milliseconds inside a GlobalScope.launch. Use delay(300) inside the coroutine. Import necessary coroutine libraries.

Kotlin

// Your code here to create a coroutine Job named job

Need a hint?

Use GlobalScope.launch to start a coroutine and assign it to job. Use repeat(5) to print "Working..." five times with delay(300) between prints.

2

Add a variable to check job status

Add a variable named isJobActive that stores the job.isActive property after starting the job.

Kotlin

import kotlinx.coroutines.*

fun main() = runBlocking {
    val job = GlobalScope.launch {
        repeat(5) {
            println("Working...")
            delay(300)
        }
    }
    job.join()
    // Add a variable isJobActive to store job.isActive
    
}

Need a hint?

After launching the job, create val isJobActive = job.isActive to check if the job is running.

3

Cancel the job and check completion

Call job.cancel() to cancel the job. Then add a variable isJobCompleted that stores job.isCompleted.

Kotlin

import kotlinx.coroutines.*

fun main() = runBlocking {
    val job = GlobalScope.launch {
        repeat(5) {
            println("Working...")
            delay(300)
        }
    }
    job.join()
    val isJobActive = job.isActive
    // Cancel the job
    // Add a variable isJobCompleted to store job.isCompleted
}

Need a hint?

Use job.cancel() to stop the job and then check job.isCompleted to see if it finished.

4

Print job status after cancellation

Print the values of isJobActive and isJobCompleted using println statements.

Kotlin

import kotlinx.coroutines.*

fun main() = runBlocking {
    val job = GlobalScope.launch {
        repeat(5) {
            println("Working...")
            delay(300)
        }
    }
    job.cancel()
    val isJobActive = job.isActive
    val isJobCompleted = job.isCompleted
    // Print isJobActive and isJobCompleted
}

Need a hint?

Use println("Job active: $isJobActive") and println("Job completed: $isJobCompleted") to show the job status.