การส่งต่อ Exception ของ async/await

async เก็บข้อยกเว้น

import kotlinx.coroutines.*
fun main() = runBlocking {
    val deferred = async {
        throw RuntimeException("async error")
    }
    try {
        deferred.await()  // exception rethrown here
    } catch (e: RuntimeException) {
        println("Caught: ${e.message}")
    }
}

ข้อยกเว้นเมื่อไม่มี await()

import kotlinx.coroutines.*
fun main() = runBlocking {
    // Exception stored in deferred, never retrieved:
    val d = async { throw RuntimeException("lost exception") }
    delay(100)  // d has failed — exception never surfaced
    println("d.isCancelled: ${d.isCancelled}")
}

async ภายใต้ coroutineScope

import kotlinx.coroutines.*
fun main() = runBlocking {
    try {
        coroutineScope {
            val a = async { "A" }
            val b = async { throw RuntimeException("B failed") }
            println(a.await())
            println(b.await())  // propagates, cancels scope
        }
    } catch (e: RuntimeException) {
        println("Scope failed: ${e.message}")
    }
}

async ภายใต้ supervisorScope

import kotlinx.coroutines.*
fun main() = runBlocking {
    supervisorScope {
        val a = async { "A" }
        val b = async { throw RuntimeException("B failed") }
        println(a.await())
        try { println(b.await()) }
        catch (e: RuntimeException) { println("b failed: ${e.message}") }
    }
}

awaitAll สำหรับ async หลายรายการ

import kotlinx.coroutines.*
fun main() = runBlocking {
    try {
        val results = awaitAll(
            async { "result1" },
            async { throw RuntimeException("task 2 failed") },
            async { "result3" }
        )
        println(results)
    } catch (e: Exception) {
        println("awaitAll failed: ${e.message}")
    }
}

runCatching กับ async

import kotlinx.coroutines.*
fun main() = runBlocking {
    supervisorScope {
        val deferreds = listOf(
            async { "A" },
            async { throw RuntimeException("B") },
            async { "C" }
        )
        val results = deferreds.map { runCatching { it.await() } }
        results.forEach { println(it) }
    }
}

งานแบบขนานกับการสะสมข้อผิดพลาด

import kotlinx.coroutines.*
fun main() = runBlocking {
    val tasks = listOf("a", "b", "c")
    val results = supervisorScope {
        tasks.map { t ->
            async {
                if (t == "b") throw RuntimeException("b failed")
                t.uppercase()
            }
        }.map { runCatching { it.await() } }
    }
    val errors = results.filter { it.isFailure }
    val successes = results.mapNotNull { it.getOrNull() }
    println("Success: $successes, Errors: ${errors.size}")
}

การคงชนิดของข้อยกเว้น

import kotlinx.coroutines.*
class NetworkException(msg: String) : RuntimeException(msg)
fun main() = runBlocking {
    val d = async { throw NetworkException("timeout") }
    try {
        d.await()
    } catch (e: NetworkException) {
        println("Network error: ${e.message}")
    } catch (e: Exception) {
        println("Other error: ${e.message}")
    }
}

Deferred.getCompleted() สำหรับการตรวจสอบแบบไม่ระงับการทำงาน

import kotlinx.coroutines.*
fun main() = runBlocking {
    val d = async { 42 }
    d.join()  // wait without caring about result
    try {
        val result = d.getCompleted()  // synchronous — no suspend
        println("Result: $result")
    } catch (e: Exception) {
        println("Failed: ${e.message}")
    }
}

การทำงานพร้อมกันแบบมีโครงสร้างกับ async

import kotlinx.coroutines.*
fun main() = runBlocking {
    val scope = CoroutineScope(SupervisorJob())
    val d = scope.async {
        delay(1000)
        "result"
    }
    scope.cancel()  // cancels d too
    try { d.await() }
    catch (e: CancellationException) { println("Cancelled as expected") }
}

แนวทางปฏิบัติที่ดี: ใช้ await เสมอ

import kotlinx.coroutines.*
fun main() = runBlocking {
    supervisorScope {
        val d = async {
            // do background work
            "done"
        }
        // Always await:
        val result = runCatching { d.await() }
        println(result)
    }
}

ตรวจสอบความเข้าใจอย่างรวดเร็ว

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