Single-flight Call.join to stop concurrent-join race #1764
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| /* | ||
| * Copyright (c) 2014-2026 Stream.io Inc. All rights reserved. | ||
| * | ||
| * Licensed under the Stream License; | ||
| * you may not use this file except in compliance with the License. | ||
| * You may obtain a copy of the License at | ||
| * | ||
| * https://github.com/GetStream/stream-video-android/blob/main/LICENSE | ||
| * | ||
| * 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. | ||
| */ | ||
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| package io.getstream.video.android.core.utils | ||
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| // package io.getstream.android.core.internal.processing | ||
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| import kotlinx.coroutines.CancellationException | ||
| import kotlinx.coroutines.CoroutineScope | ||
| import kotlinx.coroutines.Deferred | ||
| import kotlinx.coroutines.NonCancellable | ||
| import kotlinx.coroutines.async | ||
| import kotlinx.coroutines.channels.ClosedSendChannelException | ||
| import kotlinx.coroutines.sync.Mutex | ||
| import kotlinx.coroutines.sync.withLock | ||
| import kotlinx.coroutines.withContext | ||
| import java.util.concurrent.atomic.AtomicBoolean | ||
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| /** | ||
| * Single-flight that coalesces concurrent calls by key, runs the shared work on [scope], | ||
| * and tracks how many callers are still awaiting. | ||
| * | ||
| * Compared to [StreamSingleFlightProcessorImpl]: | ||
| * - Cancelling **one** waiter does **not** cancel the shared job (work is owned by [scope]). | ||
| * - Cancelling the **last** waiter **does** cancel the shared job (sole-caller cancel still | ||
| * aborts the operation). | ||
| * - [CancellationException] is rethrown to the cancelled waiter instead of being wrapped in | ||
| * [Result.failure]. | ||
| * | ||
| * Use this when the operation should survive Activity/ViewModel teardown of some waiters | ||
| * (e.g. screen handoff, UI join + call-scoped auto-join) but should not keep running after | ||
| * nobody is waiting — unless [scope] itself is cancelled (leave / call cleanup). | ||
| * | ||
| * Candidate for Stream Android Core v2 alongside [StreamSingleFlightProcessorImpl]. | ||
|
Contributor
There was a problem hiding this comment. Re-ran this at HEAD after On the KDoc though: Two things that point the same way: |
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| */ | ||
| internal class StreamRefCountedSingleFlightProcessor( | ||
| private val scope: CoroutineScope, | ||
| ) { | ||
| private class Flight<T>( | ||
| val deferred: Deferred<Result<T>>, | ||
| var waiters: Int, | ||
| ) | ||
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| private val mutex = Mutex() | ||
| private val flights = mutableMapOf<String, Flight<*>>() | ||
| private val closed = AtomicBoolean(false) | ||
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| /** | ||
| * Runs [block] once for [key] while concurrent callers await the same result. | ||
| * | ||
| * Returns [Result.failure] with a [ClosedSendChannelException] if [stop] has already | ||
| * been called. [CancellationException] is still rethrown when this waiter (or the shared | ||
| * job, including last-waiter cancel) is cancelled. | ||
| */ | ||
| @Suppress("UNCHECKED_CAST") | ||
| suspend fun <T> run(key: String, block: suspend () -> T): Result<T> { | ||
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Check failure on line 69 in stream-video-android-core/src/main/kotlin/io/getstream/video/android/core/utils/StreamRefCountedSingleFlightProcessor.kt
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| if (closed.get()) { | ||
| return Result.failure(ClosedSendChannelException("RefCountedSingleFlight is closed")) | ||
| } | ||
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| val flight = mutex.withLock { | ||
| val running = flights[key]?.takeUnless { it.deferred.isCompleted } as Flight<T>? | ||
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| if (running != null) { | ||
| running.waiters++ | ||
| running | ||
| } else { | ||
| val deferred = scope.async { | ||
| try { | ||
| // Complete normally even when [block] fails so the scope does not see an | ||
| // uncaught child exception; waiters receive Result.failure after await. | ||
| try { | ||
| Result.success(block()) | ||
| } catch (ce: CancellationException) { | ||
| throw ce | ||
| } catch (t: Throwable) { | ||
| Result.failure(t) | ||
| } | ||
| } finally { | ||
| mutex.withLock { | ||
| if (flights[key]?.deferred === this@async) { | ||
| flights.remove(key) | ||
| } | ||
| } | ||
| } | ||
| } | ||
| Flight(deferred = deferred, waiters = 1).also { flights[key] = it } | ||
| } | ||
| } | ||
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| var released = false | ||
| suspend fun releaseWaiter(cancelIfLast: Boolean) { | ||
| if (released) return | ||
| released = true | ||
| val shouldCancelShared = mutex.withLock { | ||
| flight.waiters = (flight.waiters - 1).coerceAtLeast(0) | ||
| cancelIfLast && flight.waiters == 0 && flight.deferred.isActive | ||
| } | ||
| if (shouldCancelShared) { | ||
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| flight.deferred.cancel() | ||
| } | ||
| } | ||
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| return try { | ||
| flight.deferred.await() | ||
| } catch (ce: CancellationException) { | ||
| // NonCancellable: waiter bookkeeping must run while this coroutine is cancelling. | ||
| withContext(NonCancellable) { | ||
| releaseWaiter(cancelIfLast = true) | ||
| } | ||
| throw ce | ||
| } finally { | ||
| withContext(NonCancellable) { | ||
| releaseWaiter(cancelIfLast = false) | ||
| } | ||
| } | ||
| } | ||
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| fun has(key: String): Boolean = flights.containsKey(key) | ||
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| fun cancel(key: String): Result<Unit> = runCatching { | ||
| flights[key]?.deferred?.cancel() | ||
| } | ||
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| fun clear(cancelRunning: Boolean): Result<Unit> = runCatching { | ||
| if (cancelRunning) { | ||
| flights.values.forEach { it.deferred.cancel() } | ||
| } | ||
| flights.clear() | ||
| } | ||
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| fun stop(): Result<Unit> = runCatching { | ||
| if (closed.compareAndSet(false, true)) { | ||
| clear(cancelRunning = true).getOrThrow() | ||
| } | ||
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| } | ||
| } | ||
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