| Yigit Boyar | f367380 | 2020-12-28 12:08:30 -0800 | [diff] [blame] | 1 | /* |
| 2 | * Copyright 2020 The Android Open Source Project |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
| 16 | |
| 17 | package androidx.paging |
| 18 | |
| 19 | import kotlinx.coroutines.CoroutineScope |
| 20 | import kotlinx.coroutines.Job |
| 21 | import kotlinx.coroutines.channels.Channel |
| 22 | import kotlinx.coroutines.channels.SendChannel |
| 23 | import kotlinx.coroutines.coroutineScope |
| 24 | import kotlinx.coroutines.flow.Flow |
| 25 | import kotlinx.coroutines.flow.buffer |
| 26 | import kotlinx.coroutines.flow.flow |
| 27 | import kotlinx.coroutines.flow.internal.FusibleFlow |
| 28 | import kotlinx.coroutines.launch |
| 29 | import kotlinx.coroutines.suspendCancellableCoroutine |
| 30 | import kotlin.coroutines.resume |
| 31 | |
| 32 | /** |
| 33 | * This is a simplified channelFlow implementation as a temporary measure until channel flow |
| 34 | * leaves experimental state. |
| 35 | * |
| 36 | * The exact same implementation is not possible due to [FusibleFlow] being an internal API. To |
| 37 | * get close to that implementation, internally we use a [Channel.RENDEZVOUS] channel and use a |
| 38 | * [buffer] ([Channel.BUFFERED]) operator on the resulting Flow. This gives us a close behavior |
| 39 | * where the default is buffered and any followup buffer operation will result in +1 value being |
| 40 | * produced. |
| 41 | */ |
| 42 | internal fun <T> simpleChannelFlow( |
| 43 | block: suspend SimpleProducerScope<T>.() -> Unit |
| 44 | ): Flow<T> { |
| 45 | return flow { |
| 46 | coroutineScope { |
| 47 | val channel = Channel<T>(capacity = Channel.RENDEZVOUS) |
| 48 | val producer = launch { |
| 49 | try { |
| 50 | // run producer in a separate inner scope to ensure we wait for its children |
| 51 | // to finish, in case it does more launches inside. |
| 52 | coroutineScope { |
| 53 | val producerScopeImpl = SimpleProducerScopeImpl( |
| 54 | scope = this, |
| 55 | channel = channel, |
| 56 | ) |
| 57 | producerScopeImpl.block() |
| 58 | } |
| 59 | channel.close() |
| 60 | } catch (t: Throwable) { |
| 61 | channel.close(t) |
| 62 | } |
| 63 | } |
| 64 | for (item in channel) { |
| 65 | emit(item) |
| 66 | } |
| 67 | // in case channel closed before producer completes, cancel the producer. |
| 68 | producer.cancel() |
| 69 | } |
| 70 | }.buffer(Channel.BUFFERED) |
| 71 | } |
| 72 | |
| 73 | internal interface SimpleProducerScope<T> : CoroutineScope, SendChannel<T> { |
| 74 | val channel: SendChannel<T> |
| 75 | suspend fun awaitClose(block: () -> Unit) |
| 76 | } |
| 77 | |
| 78 | internal class SimpleProducerScopeImpl<T>( |
| 79 | scope: CoroutineScope, |
| 80 | override val channel: SendChannel<T>, |
| 81 | ) : SimpleProducerScope<T>, CoroutineScope by scope, SendChannel<T> by channel { |
| 82 | override suspend fun awaitClose(block: () -> Unit) { |
| 83 | try { |
| 84 | val job = checkNotNull(coroutineContext[Job]) { |
| 85 | "Internal error, context should have a job." |
| 86 | } |
| 87 | suspendCancellableCoroutine<Unit> { cont -> |
| 88 | job.invokeOnCompletion { |
| 89 | cont.resume(Unit) |
| 90 | } |
| 91 | } |
| 92 | } finally { |
| 93 | block() |
| 94 | } |
| 95 | } |
| 96 | } |
