ListenableFuture.kt

/*
 * Copyright 2018 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

@file:Suppress("NOTHING_TO_INLINE")

package androidx.work

import androidx.annotation.RestrictTo
import androidx.work.impl.utils.futures.SettableFuture
import com.google.common.util.concurrent.ListenableFuture
import kotlinx.coroutines.Job
import kotlinx.coroutines.suspendCancellableCoroutine
import java.util.concurrent.CancellationException
import java.util.concurrent.ExecutionException
import kotlin.coroutines.resume
import kotlin.coroutines.resumeWithException

/**
 * Awaits for the completion of the [ListenableFuture] without blocking a thread.
 *
 * @return R The result from the [ListenableFuture]
 *
 * @hide
 */
@RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
public suspend inline fun <R> ListenableFuture<R>.await(): R {
    // Fast path
    if (isDone) {
        try {
            return get()
        } catch (e: ExecutionException) {
            throw e.cause ?: e
        }
    }
    return suspendCancellableCoroutine { cancellableContinuation ->
        addListener(
            Runnable {
                try {
                    cancellableContinuation.resume(get())
                } catch (throwable: Throwable) {
                    val cause = throwable.cause ?: throwable
                    when (throwable) {
                        is CancellationException -> cancellableContinuation.cancel(cause)
                        else -> cancellableContinuation.resumeWithException(cause)
                    }
                }
            },
            DirectExecutor.INSTANCE
        )
    }
}

/**
 * A special [Job] to [ListenableFuture] wrapper.
 */
internal class JobListenableFuture<R>(
    private val job: Job,
    private val underlying: SettableFuture<R> = SettableFuture.create()
) : ListenableFuture<R> by underlying {

    public fun complete(result: R) {
        underlying.set(result)
    }

    init {
        job.invokeOnCompletion { throwable: Throwable? ->
            when (throwable) {
                null -> require(underlying.isDone)
                is CancellationException -> underlying.cancel(true)
                else -> underlying.setException(throwable.cause ?: throwable)
            }
        }
    }
}