java Executor 인터페이스와 kotlin ExecutorCoroutineDisatcher 의 차이에 대해 알아보자

Executor Interface

자바의 java.util.concurrent 패키지에 있는 Excutor interface 는 인자로 Runnable을 입력받아 해당 task 를 실행하는 execute 메소드를 단일 메소드로 가지는 interface다.

Executor interface 의 기능을 확장하는 ExecutorService interface 를 주로 사용하며

스레드풀을 관리하여 주어지는 task 들을 수행하는 ThreadPoolExecutor를 가 가장 많이 사용된다.

public interface Executor {

    /**
     * Executes the given command at some time in the future.  The command
     * may execute in a new thread, in a pooled thread, or in the calling
     * thread, at the discretion of the {@code Executor} implementation.
     *
     * @param command the runnable task
     * @throws RejectedExecutionException if this task cannot be
     * accepted for execution
     * @throws NullPointerException if command is null
     */
    void execute(Runnable command);
}

public interface ExecutorService extends Executor {

    void shutdown();

    List<Runnable> shutdownNow();

    boolean isShutdown();

    boolean isTerminated();

    boolean awaitTermination(long timeout, TimeUnit unit)
        throws InterruptedException;

    <T> Future<T> submit(Callable<T> task);

    <T> Future<T> submit(Runnable task, T result);

    <T> Future<?> submit(Runnable task);

    <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
        throws InterruptedException;

    <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
                                  long timeout, TimeUnit unit)
        throws InterruptedException;

    <T> T invokeAny(Collection<? extends Callable<T>> tasks)
        throws InterruptedException, ExecutionException;

    <T> T invokeAny(Collection<? extends Callable<T>> tasks,
                    long timeout, TimeUnit unit)
        throws InterruptedException, ExecutionException, TimeoutException;
}

ExecutorCoroutineDispatcher

kotlinx.coroutines 패키지에 있는 ExecutorCoroutineDispatcher 는 java Executor interface 와 kotlin의 CoroutineDispatcher 의 상호호환을 도와주는 interface다.

public abstract class ExecutorCoroutineDispatcher: CoroutineDispatcher(), Closeable {
    /** @suppress */
    @ExperimentalStdlibApi
    public companion object Key : AbstractCoroutineContextKey<CoroutineDispatcher, ExecutorCoroutineDispatcher>(
        CoroutineDispatcher,
        { it as? ExecutorCoroutineDispatcher })

    /**
     * Underlying executor of current [CoroutineDispatcher].
     */
    public abstract val executor: Executor

    /**
     * Closes this coroutine dispatcher and shuts down its executor.
     *
     * It may throw an exception if this dispatcher is global and cannot be closed.
     */
    public abstract override fun close()
}

해당 패키지에는 java ExecutorService 와 kotlin CoroutineDispatcher 를 서로 변환해주는 확장 함수들이 존재한다.

@JvmName("from") // this is for a nice Java API, see issue #255
public fun ExecutorService.asCoroutineDispatcher(): ExecutorCoroutineDispatcher =
    ExecutorCoroutineDispatcherImpl(this)
    
@JvmName("from") // this is for a nice Java API, see issue #255
public fun Executor.asCoroutineDispatcher(): CoroutineDispatcher =
    (this as? DispatcherExecutor)?.dispatcher ?: ExecutorCoroutineDispatcherImpl(this)

public fun CoroutineDispatcher.asExecutor(): Executor =
    (this as? ExecutorCoroutineDispatcher)?.executor ?: DispatcherExecutor(this)

private class DispatcherExecutor(@JvmField val dispatcher: CoroutineDispatcher) : Executor {
    override fun execute(block: Runnable) = dispatcher.dispatch(EmptyCoroutineContext, block)
    override fun toString(): String = dispatcher.toString()
}