코루틴 컨텍스트 (CoroutineContext)

코루틴 컨텍스트 (CoroutineContext)

• Job 계층의 생명 주기를 연결하기 위해 사용

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코루틴 컨텍스트 구현체

// kotlin.coroutines.CoroutineContext.class

@kotlin.SinceKotlin public interface CoroutineContext {
    public abstract operator fun <E : kotlin.coroutines.CoroutineContext.Element> get(key: kotlin.coroutines.CoroutineContext.Key<E>): E?

    public abstract fun <R> fold(initial: R, operation: (R, kotlin.coroutines.CoroutineContext.Element) -> R): R

    public open operator fun plus(context: kotlin.coroutines.CoroutineContext): kotlin.coroutines.CoroutineContext { /* compiled code */ }

    public abstract fun minusKey(key: kotlin.coroutines.CoroutineContext.Key<*>): kotlin.coroutines.CoroutineContext

    public interface Key<E : kotlin.coroutines.CoroutineContext.Element> {
    }

    public interface Element : kotlin.coroutines.CoroutineContext {
        public abstract val key: kotlin.coroutines.CoroutineContext.Key<*>

        public open operator fun <E : kotlin.coroutines.CoroutineContext.Element> get(key: kotlin.coroutines.CoroutineContext.Key<E>): E? { /* compiled code */ }

        public open fun <R> fold(initial: R, operation: (R, kotlin.coroutines.CoroutineContext.Element) -> R): R { /* compiled code */ }

        public open fun minusKey(key: kotlin.coroutines.CoroutineContext.Key<*>): kotlin.coroutines.CoroutineContext { /* compiled code */ }
    }
}

• Composite Design Pattern(복합체 패턴)을 이용하여 중첩된 스코프의 실행 위치를 추적할 수 있도록 설계
• CoroutineScope는 CoroutineContext의 컨테이너 역할을 하여 Job을 그룹화 시킴
• CoroutineContext는 코루틴 동작을 설명하는 요소들의 집합

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코루틴 컨텍스트 특징

• 병합하거나 분해할 수 있음
  • EmptyCoroutineContext → 요소가 없는 상태
  • Element → 요소가 하나인 상태
  • CombinedContext → 요소가 2개 이상인 상태
  • Key → 요소를 구분할 때 사용하는 식별자

fun main() {
    val handler = CoroutineExceptionHandler { _, e ->
        println("CoroutineExceptionHandler")
    }

    val context1 = CoroutineName("Custom Coroutine") +
            Dispatchers.Default +
            Job() +
            handler

    println("context: $context1")

    val context2 = context1.minusKey(CoroutineExceptionHandler)
    println("context2: $context2")

    val context3 = context2.minusKey(Job)
    println("context3: $context3")

    val context4 = context3.minusKey(CoroutineDispatcher)
    println("context4: $context4")

    val context5 = context4.minusKey(CoroutineName)
    println("context5: $context5")
}

/*
실행 결과:
context: [CoroutineName(Custom Coroutine), JobImpl{Active}@5197848c, TestKt$main$$inlined$CoroutineExceptionHandler$1@17f052a3, Dispatchers.Default]
context2: [CoroutineName(Custom Coroutine), JobImpl{Active}@5197848c, Dispatchers.Default]
context3: [CoroutineName(Custom Coroutine), Dispatchers.Default]
context4: CoroutineName(Custom Coroutine)
context5: EmptyCoroutineContext
*/

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Job

• CoroutineContext의 요소

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Job 구현체

// kotlinx.coroutines.Job.kt

@Suppress("FunctionName")
public fun Job(parent: Job? = null): CompletableJob = JobImpl(parent)

// kotlinx.coroutines.CompletableJob.kt

@OptIn(ExperimentalSubclassOptIn::class)
@SubclassOptInRequired(markerClass = InternalForInheritanceCoroutinesApi::class)
public interface CompletableJob : Job {
    
    public fun complete(): Boolean

    public fun completeExceptionally(exception: Throwable): Boolean
}

// kotlinx.coroutines.Job.kt

@OptIn(ExperimentalSubclassOptIn::class)
@SubclassOptInRequired(markerClass = InternalForInheritanceCoroutinesApi::class)
public interface Job : CoroutineContext.Element {
   
   public companion object Key : CoroutineContext.Key<Job>
	 
	 public val parent: Job?  
	 
	 public val isActive: Boolean
	 
	 public val isCompleted: Boolean
	 
	 public val isCancelled: Boolean 
	 
	 public fun getCancellationException(): CancellationException
	 
	 public fun start(): Boolean
	 
	 public fun cancel(cause: CancellationException? = null)
	 
	 public val children: Sequence<Job>
	 
	 public fun attachChild(child: ChildJob): ChildHandle
	 
	 public suspend fun join()
	 
	 public val onJoin: SelectClause0
	 
	 public fun invokeOnCompletion(handler: CompletionHandler): DisposableHandle
	 
	 public fun invokeOnCompletion(
        onCancelling: Boolean = false,
        invokeImmediately: Boolean = true,
        handler: CompletionHandler): DisposableHandle
}

• 상태를 가짐
  • Active
  • Completed
  • Cancelled
• start, cancel을 통해 명시적으로 작업 가능
• children을 통해 다른 Job의 생명주기 관리 가능

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코루틴 디스패쳐(Coroutine Dispatcher)

• 스레드간 코루틴을 분산하는 orchestrator
• 코루틴을 실행하고자 하는 스레드를 지정하는 역할

---

Coroutine Dispatcher 구현체

// kotlinx.coroutines.Dispatchers.kt

public actual object Dispatchers {
    @JvmStatic
    public actual val Default: CoroutineDispatcher = DefaultScheduler

    @JvmStatic
    public actual val Main: MainCoroutineDispatcher get() = MainDispatcherLoader.dispatcher

    @JvmStatic
    public actual val Unconfined: CoroutineDispatcher = kotlinx.coroutines.Unconfined
    
    @JvmStatic
    public val IO: CoroutineDispatcher get() = DefaultIoScheduler
    
    @DelicateCoroutinesApi
    public fun shutdown() {
        DefaultExecutor.shutdown()
        // Also shuts down Dispatchers.IO
        DefaultScheduler.shutdown()
    }
}

• Default
  • CPU 개수만큼 스레드 생성
  • CPU를 많이 사용하는 무거운 작업에 최적화
• Main
  • 화면 UI 작업을 위해 사용
  • Android 개발 모듈에서 주로 사용
• IO
  • 최대 64개까지 늘어나는 가변 크기의 스레드 풀 사용
    • kotlinx.coroutines.io.parallelism 로 조절 가능
  • 네트워크, DB I/O 등 사용
  • 읽기, 쓰기 작업에 최적화
  • Thread를 Block할 필요가 있는 경우