Careeroza

Real World Example

Flipkart Checkout: All or Nothing

At checkout, the app must reserve stock and charge the payment. If payment fails, the stock reservation must be cancelled and released. coroutineScope gives exactly this: one failure cancels the sibling, and a finally block does the cleanup.

checkout()
  coroutineScope
   ├─ launch reserveStock()   ── cancelled ──► finally: release stock
   └─ launch chargePayment()  ── FAILS (card declined)
  → exception reaches checkout(), user sees "Payment failed"

Code

Example

import kotlinx.coroutines.*

class PaymentException(msg: String) : Exception(msg)

suspend fun reserveStock(sku: String) {
    println("Reserving $sku...")
    try {
        delay(500)
        println("Reserved $sku")
    } catch (e: CancellationException) {
        println("Released reservation for $sku")
        throw e
    }
}

suspend fun chargePayment(amount: Int, card: String) {
    delay(200)
    if (card.endsWith("0000")) throw PaymentException("Card declined for Rs $amount")
    println("Charged Rs $amount")
}

suspend fun checkout(sku: String, amount: Int, card: String): String = try {
    coroutineScope {
        launch { reserveStock(sku) }
        launch { chargePayment(amount, card) }
    }
    "Order confirmed"
} catch (e: PaymentException) {
    "Payment failed: ${e.message}"
}

fun main() = runBlocking {
    println(checkout("PHONE-128GB", 15999, "4111-1111-1111-1111"))
    println("---")
    println(checkout("LAPTOP-16GB", 54999, "4000-0000-0000-0000"))
}

Output

Reserving PHONE-128GB...
Charged Rs 15999
Reserved PHONE-128GB
Order confirmed
---
Reserving LAPTOP-16GB...
Released reservation for LAPTOP-16GB
Payment failed: Card declined for Rs 54999