| package kotlinx.coroutines.experimental |
| |
| import kotlin.coroutines.CoroutineContext |
| import kotlin.coroutines.startCoroutine |
| |
| /** |
| * Deferred value is conceptually a non-blocking cancellable future. |
| * It is created with [defer] coroutine builder. |
| */ |
| public interface Deferred<out T> : Job { |
| /** |
| * Awaits for completion of this value without blocking a thread and resumes when deferred computation is complete. |
| * This suspending function is cancellable. |
| * If the [Job] of the current coroutine is completed while this suspending function is waiting, this function |
| * immediately resumes with [CancellationException]. |
| */ |
| public suspend fun await(): T |
| |
| /** |
| * Returns *completed* result or throws [IllegalStateException] if this deferred value is still [isActive]. |
| * It throws the corresponding exception if this deferred has completed exceptionally. |
| * This function is designed to be used from [onCompletion] handlers, when there is an absolute certainty that |
| * the value is already complete. |
| */ |
| public fun getCompleted(): T |
| } |
| |
| /** |
| * Starts new coroutine and returns its result as an implementation of [Deferred]. |
| * The running coroutine is cancelled when the resulting job is cancelled. |
| * The [context] for the new coroutine must be explicitly specified and must include [CoroutineDispatcher] element. |
| * The specified context is added to the context of the parent running coroutine (if any) inside which this function |
| * is invoked. The [Job] of the resulting coroutine is a child of the job of the parent coroutine (if any). |
| */ |
| public fun <T> defer(context: CoroutineContext, block: suspend () -> T) : Deferred<T> = |
| DeferredCoroutine<T>(newCoroutineContext(context)).also { block.startCoroutine(it) } |
| |
| private class DeferredCoroutine<T>( |
| parentContext: CoroutineContext |
| ) : JobContinuation<T>(parentContext), Deferred<T> { |
| @Suppress("UNCHECKED_CAST") |
| suspend override fun await(): T { |
| // quick check if already complete (avoid extra object creation) |
| val state = getState() |
| if (state !is Active) { |
| if (state is CompletedExceptionally) throw state.exception |
| return state as T |
| } |
| // Note: await is cancellable itself! |
| return awaitGetValue() |
| } |
| |
| @Suppress("UNCHECKED_CAST") |
| private suspend fun awaitGetValue(): T = suspendCancellableCoroutine { cont -> |
| cont.unregisterOnCompletion(onCompletion { |
| val state = getState() |
| check(state !is Active) |
| if (state is CompletedExceptionally) |
| cont.resumeWithException(state.exception) |
| else |
| cont.resume(state as T) |
| }) |
| } |
| |
| @Suppress("UNCHECKED_CAST") |
| override fun getCompleted(): T { |
| val state = getState() |
| check(state !is Active) { "This deferred value is still active" } |
| if (state is CompletedExceptionally) throw state.exception |
| return state as T |
| } |
| } |