| /* |
| * Copyright 2019 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.room |
| |
| import java.util.ArrayDeque |
| import java.util.concurrent.Executor |
| |
| /** |
| * Executor wrapper for performing database transactions serially. |
| * |
| * Since database transactions are exclusive, this executor ensures that transactions are performed |
| * in-order and one at a time, preventing threads from blocking each other when multiple concurrent |
| * transactions are attempted. |
| */ |
| internal class TransactionExecutor(private val executor: Executor) : Executor { |
| private val tasks = ArrayDeque<Runnable>() |
| private var active: Runnable? = null |
| private val syncLock = Any() |
| override fun execute(command: Runnable) { |
| synchronized(syncLock) { |
| tasks.offer(Runnable { |
| try { |
| command.run() |
| } finally { |
| scheduleNext() |
| } |
| }) |
| if (active == null) { |
| scheduleNext() |
| } |
| } |
| } |
| |
| fun scheduleNext() { |
| synchronized(syncLock) { |
| if (tasks.poll().also { active = it } != null) { |
| executor.execute(active) |
| } |
| } |
| } |
| } |