Roman Elizarov | 3754f95 | 2017-01-18 20:47:54 +0300 | [diff] [blame^] | 1 | package kotlinx.coroutines.experimental |
| 2 | |
| 3 | import kotlin.coroutines.CoroutineContext |
| 4 | import kotlin.coroutines.startCoroutine |
| 5 | |
| 6 | /** |
| 7 | * Deferred value is conceptually a non-blocking cancellable future. |
| 8 | * It is created with [defer] coroutine builder. |
| 9 | */ |
| 10 | public interface Deferred<out T> : Job { |
| 11 | /** |
| 12 | * Awaits for completion of this value without blocking a thread and resumes when deferred computation is complete. |
| 13 | * This suspending function is cancellable. |
| 14 | * If the [Job] of the current coroutine is completed while this suspending function is waiting, this function |
| 15 | * immediately resumes with [CancellationException] . |
| 16 | */ |
| 17 | public suspend fun await(): T |
| 18 | } |
| 19 | |
| 20 | /** |
| 21 | * Starts new coroutine and returns its result as an implementation of [Deferred]. |
| 22 | * The running coroutine is cancelled when the resulting job is cancelled. |
| 23 | * The [context] for the new coroutine must be explicitly specified and must include [CoroutineDispatcher] element. |
| 24 | * The specified context is added to the context of the parent running coroutine (if any) inside which this function |
| 25 | * is invoked. The [Job] of the resulting coroutine is a child of the job of the parent coroutine (if any). |
| 26 | */ |
| 27 | public fun <T> defer(context: CoroutineContext, block: suspend () -> T) : Deferred<T> = |
| 28 | DeferredCoroutine<T>(newCoroutineContext(context)).also { block.startCoroutine(it) } |
| 29 | |
| 30 | private class DeferredCoroutine<T>( |
| 31 | parentContext: CoroutineContext |
| 32 | ) : JobContinuation<T>(parentContext), Deferred<T> { |
| 33 | @Suppress("UNCHECKED_CAST") |
| 34 | suspend override fun await(): T { |
| 35 | // quick check if already complete (avoid extra object creation) |
| 36 | val state = getState() |
| 37 | if (state !is Active) { |
| 38 | if (state is CompletedExceptionally) throw state.exception |
| 39 | return state as T |
| 40 | } |
| 41 | // Note: await is cancellable itself! |
| 42 | return awaitGetValue() |
| 43 | } |
| 44 | |
| 45 | @Suppress("UNCHECKED_CAST") |
| 46 | private suspend fun awaitGetValue(): T = suspendCancellableCoroutine { cont -> |
| 47 | cont.unregisterOnCompletion(onCompletion { |
| 48 | val state = getState() |
| 49 | check(state !is Active) |
| 50 | if (state is CompletedExceptionally) |
| 51 | cont.resumeWithException(state.exception) |
| 52 | else |
| 53 | cont.resume(state as T) |
| 54 | }) |
| 55 | } |
| 56 | |
| 57 | override fun afterCompletion(state: Any?, closeException: Throwable?) { |
| 58 | if (closeException != null) handleCoroutineException(context, closeException) |
| 59 | } |
| 60 | } |