Kotlin resumeWithException Function

The resumeWithException function in Kotlin is used to resume the execution of a suspended coroutine with an exception. This function is part of the Kotlin coroutines library (kotlinx.coroutines). It allows you to manually control the execution flow of a coroutine by resuming it with an error, which is particularly useful in advanced coroutine scenarios.

Table of Contents

1. Introduction
2. resumeWithException Function Syntax
3. Understanding resumeWithException
4. Examples
   • Basic Usage
   • Handling Exceptions in Coroutines
5. Real-World Use Case
6. Conclusion

Introduction

The resumeWithException function allows you to resume a coroutine that has been suspended by throwing an exception. When a coroutine is resumed with an exception, the exception is propagated to the point where the coroutine was suspended. This gives you fine-grained control over the coroutine’s error handling.

resumeWithException Function Syntax

The syntax for the resumeWithException function is as follows:

fun <T> Continuation<T>.resumeWithException(exception: Throwable) 

Parameters:

• exception: The exception with which to resume the coroutine.

Returns:

• The function does not return a value.

Understanding resumeWithException

The resumeWithException function is used to continue the execution of a suspended coroutine by throwing an exception. If the coroutine was suspended with a certain continuation, calling resumeWithException on that continuation will resume the coroutine and propagate the exception to the point where it was suspended. This allows the coroutine to handle the exception as needed.

Examples

Basic Usage

To demonstrate the basic usage of resumeWithException, we will create a simple coroutine and resume it with an exception manually.

Example

import kotlin.coroutines.* fun main() { val suspendingLambda: suspend () -> Unit = { println("Coroutine started") // Simulate suspension point suspendCoroutine<Unit> { continuation -> println("Coroutine suspended") // Manually resume the coroutine with an exception continuation.resumeWithException(RuntimeException("Error occurred")) } } val continuation = suspendingLambda.createCoroutine(object : Continuation<Unit> { override val context: CoroutineContext = EmptyCoroutineContext override fun resumeWith(result: Result<Unit>) { result.onSuccess { println("Coroutine completed successfully") }.onFailure { exception -> println("Coroutine failed with exception: $exception") } } }) println("Starting coroutine") continuation.resume(Unit) } 

Output:

Starting coroutine Coroutine started Coroutine suspended Coroutine failed with exception: java.lang.RuntimeException: Error occurred 

Handling Exceptions in Coroutines

This example shows how to handle exceptions in a coroutine that is resumed with an exception.

Example

import kotlin.coroutines.* suspend fun mySuspendingFunction() { return suspendCoroutine { continuation -> println("Suspending function executed") // Simulate an error condition continuation.resumeWithException(RuntimeException("Error in suspending function")) } } fun main() { val suspendingLambda: suspend () -> Unit = { try { mySuspendingFunction() } catch (e: Exception) { println("Caught exception: ${e.message}") } } val continuation = suspendingLambda.createCoroutine(object : Continuation<Unit> { override val context: CoroutineContext = EmptyCoroutineContext override fun resumeWith(result: Result<Unit>) { result.onSuccess { println("Coroutine completed successfully") }.onFailure { exception -> println("Coroutine failed with exception: $exception") } } }) println("Starting coroutine") continuation.resume(Unit) } 

Output:

Starting coroutine Suspending function executed Caught exception: Error in suspending function Coroutine completed successfully 

Real-World Use Case

Handling Network Request Errors

In real-world applications, the resumeWithException function can be used to handle errors in asynchronous operations, such as network requests, by resuming coroutines with exceptions when errors occur.

Example

import kotlin.coroutines.* suspend fun fetchData(): String { return suspendCoroutine { continuation -> println("Fetching data...") // Simulate network request Thread.sleep(2000) // Simulate network error continuation.resumeWithException(RuntimeException("Network error")) } } fun main() { val suspendingLambda: suspend () -> Unit = { try { val data = fetchData() println("Coroutine resumed with data: $data") } catch (e: Exception) { println("Caught exception: ${e.message}") } } val continuation = suspendingLambda.createCoroutine(object : Continuation<Unit> { override val context: CoroutineContext = EmptyCoroutineContext override fun resumeWith(result: Result<Unit>) { result.onSuccess { println("Coroutine completed successfully") }.onFailure { exception -> println("Coroutine failed with exception: $exception") } } }) println("Starting coroutine") continuation.resume(Unit) } 

Output:

Starting coroutine Fetching data... Caught exception: Network error Coroutine completed successfully 

Conclusion

The resumeWithException function in Kotlin provides used for resuming suspended coroutines with an exception. By understanding and using the resumeWithException function, you can effectively manage error handling in your Kotlin applications, allowing for advanced asynchronous programming techniques and greater control over coroutine behavior.