What are Kotlin coroutines and how do they differ from threads?

Overview

Coroutines are lightweight concurrency primitives that suspend execution instead of blocking threads.

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Coroutines vs Threads

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Basic Usage

Threads

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Thread {
    val data = fetchData()
    runOnUiThread {
        updateUI(data)
    }
}.start()

Coroutines

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viewModelScope.launch {
    val data = withContext(Dispatchers.IO) {
        fetchData()
    }
    updateUI(data) // Auto on main thread
}

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Dispatchers

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// Main thread (UI updates)
Dispatchers.Main

// Background (network, DB)
Dispatchers.IO

// CPU-intensive work
Dispatchers.Default

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async/await

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viewModelScope.launch {
    val user = async { fetchUser() }
    val posts = async { fetchPosts() }
    
    val userData = user.await()
    val postsData = posts.await()
}

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Cancellation

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val job = viewModelScope.launch {
    repeat(1000) {
        delay(100)
        // Work
    }
}

job.cancel() // ✅ Clean cancellation

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Structured Concurrency

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viewModelScope.launch {
    val job1 = launch { task1() }
    val job2 = launch { task2() }
    // Both cancelled when viewModelScope is cleared
}

Key Advantage: 10,000 coroutines use same memory as 10 threads.