| /* |
| * Copyright 2020 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.compose |
| |
| import kotlinx.coroutines.suspendCancellableCoroutine |
| import kotlin.coroutines.Continuation |
| import kotlin.coroutines.resume |
| |
| /** |
| * A boolean open or closed latch for awaiting a single repeating event, like pending |
| * recompositions. Closing while already closed or opening while already open is a no-op; |
| * only one event producer should be responsible for opening or closing the latch. |
| * |
| * This implementation is intended for low-contention environments involving |
| * low total numbers of threads in a pool on the order of ~number of CPU cores available for UI |
| * recomposition work, while avoiding additional allocation where possible. |
| */ |
| internal class Latch { |
| |
| private val lock = Any() |
| private var awaiters = mutableListOf<Continuation<Unit>>() |
| private var spareList = mutableListOf<Continuation<Unit>>() |
| |
| private var _isOpen = true |
| val isOpen get() = synchronized(lock) { _isOpen } |
| |
| inline fun <R> withClosed(block: () -> R): R { |
| closeLatch() |
| return try { |
| block() |
| } finally { |
| openLatch() |
| } |
| } |
| |
| fun closeLatch() { |
| synchronized(lock) { |
| _isOpen = false |
| } |
| } |
| |
| fun openLatch() { |
| synchronized(lock) { |
| if (isOpen) return |
| |
| // Rotate the lists so that if a resumed continuation on an immediate dispatcher |
| // bound to the thread calling openLatch immediately awaits again we don't disrupt |
| // iteration of resuming the rest. This is also why we set isClosed before resuming. |
| val toResume = awaiters |
| awaiters = spareList |
| spareList = toResume |
| _isOpen = true |
| |
| for (i in 0 until toResume.size) { |
| toResume[i].resume(Unit) |
| } |
| toResume.clear() |
| } |
| } |
| |
| suspend fun await() { |
| if (isOpen) return |
| |
| suspendCancellableCoroutine<Unit> { co -> |
| synchronized(lock) { |
| awaiters.add(co) |
| } |
| |
| co.invokeOnCancellation { |
| synchronized(lock) { |
| awaiters.remove(co) |
| } |
| } |
| } |
| } |
| } |