1 /* 2 * Copyright 2023 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 #pragma once 18 19 #include <utils/threads.h> 20 #include <list> 21 #include <mutex> 22 #include <optional> 23 24 namespace android { 25 26 /** A thread-safe FIFO queue. */ 27 template <class T> 28 class SyncQueue { 29 public: 30 SyncQueue() = default; 31 SyncQueue(size_t capacity)32 SyncQueue(size_t capacity) : mCapacity(capacity) {} 33 34 /** Retrieve and remove the oldest object. Returns std::nullopt if the queue is empty. */ pop()35 std::optional<T> pop() { 36 std::scoped_lock lock(mLock); 37 if (mQueue.empty()) { 38 return {}; 39 } 40 T t = std::move(mQueue.front()); 41 mQueue.erase(mQueue.begin()); 42 return t; 43 }; 44 45 /** 46 * Add a new object to the queue. 47 * Return true if an element was successfully added. 48 * Return false if the queue is full. 49 */ 50 template <class... Args> push(Args &&...args)51 bool push(Args&&... args) { 52 std::scoped_lock lock(mLock); 53 if (mCapacity && mQueue.size() == mCapacity) { 54 return false; 55 } 56 mQueue.emplace_back(args...); 57 return true; 58 }; 59 60 private: 61 const std::optional<size_t> mCapacity; 62 std::mutex mLock; 63 std::list<T> mQueue GUARDED_BY(mLock); 64 }; 65 66 } // namespace android 67