AndroidXConsumer.kt
/*
* Copyright 2022 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.
*/
package androidx.core.util
import java.util.concurrent.atomic.AtomicBoolean
import kotlin.coroutines.Continuation
import kotlin.coroutines.resume
/**
* Returns a [Consumer] that will resume this [Continuation] when the result of an operation
* is [accepted][Consumer.accept].
*
* Useful for writing `suspend` bindings to async Jetpack library methods that accept [Consumer]
* as a result callback for a one-time operation:
*
* ```
* public suspend fun FancinessManager.query(
* query: FancinessManager.Query
* ): FancinessManager.QueryResult = suspendCancellableCoroutine<QueryResult> { continuation ->
*
* // Any Android API that supports cancellation should be configured to propagate
* // coroutine cancellation as follows:
* val canceller = CancellationSignal()
* continuation.invokeOnCancellation { canceller.cancel() }
*
* // Invoke the FancinessManager#queryAsync method as follows:
* queryAsync(
* query,
* canceller,
* // Use a direct executor to avoid extra dispatch. Resuming the continuation will
* // handle getting to the right thread or pool via the ContinuationInterceptor.
* Runnable::run,
* continuation.asAndroidXConsumer()
* )
* }
* ```
*/
public fun <T> Continuation<T>.asAndroidXConsumer(): Consumer<T> =
AndroidXContinuationConsumer(this)
private class AndroidXContinuationConsumer<T>(
private val continuation: Continuation<T>
) : Consumer<T>, AtomicBoolean(false) {
override fun accept(value: T) {
// Do not attempt to resume more than once, even if the caller of the returned
// Consumer is buggy and tries anyway.
if (compareAndSet(false, true)) {
continuation.resume(value)
}
}
override fun toString() = "ContinuationConsumer(resultAccepted = ${get()})"
}