1 /* 2 * Copyright (C) 2019 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 #ifndef _UI_INPUT_BLOCKING_QUEUE_H 18 #define _UI_INPUT_BLOCKING_QUEUE_H 19 20 #include "android-base/thread_annotations.h" 21 #include <condition_variable> 22 #include <mutex> 23 #include <vector> 24 25 namespace android { 26 27 /** 28 * A FIFO queue that stores up to <i>capacity</i> objects. 29 * Objects can always be added. Objects are added immediately. 30 * If the queue is full, new objects cannot be added. 31 * 32 * The action of retrieving an object will block until an element is available. 33 */ 34 template <class T> 35 class BlockingQueue { 36 public: BlockingQueue(size_t capacity)37 BlockingQueue(size_t capacity) : mCapacity(capacity) { 38 mQueue.reserve(mCapacity); 39 }; 40 41 /** 42 * Retrieve and remove the oldest object. 43 * Blocks execution while queue is empty. 44 */ pop()45 T pop() { 46 std::unique_lock lock(mLock); 47 android::base::ScopedLockAssertion assumeLock(mLock); 48 mHasElements.wait(lock, [this]() REQUIRES(mLock) { return !this->mQueue.empty(); }); 49 T t = std::move(mQueue.front()); 50 mQueue.erase(mQueue.begin()); 51 return t; 52 }; 53 54 /** 55 * Add a new object to the queue. 56 * Does not block. 57 * Return true if an element was successfully added. 58 * Return false if the queue is full. 59 */ push(T && t)60 bool push(T&& t) { 61 { 62 std::scoped_lock lock(mLock); 63 if (mQueue.size() == mCapacity) { 64 return false; 65 } 66 mQueue.push_back(std::move(t)); 67 } 68 mHasElements.notify_one(); 69 return true; 70 }; 71 erase(const std::function<bool (const T &)> & lambda)72 void erase(const std::function<bool(const T&)>& lambda) { 73 std::scoped_lock lock(mLock); 74 std::erase_if(mQueue, [&lambda](const auto& t) { return lambda(t); }); 75 } 76 77 /** 78 * Remove all elements. 79 * Does not block. 80 */ clear()81 void clear() { 82 std::scoped_lock lock(mLock); 83 mQueue.clear(); 84 }; 85 86 /** 87 * How many elements are currently stored in the queue. 88 * Primary used for debugging. 89 * Does not block. 90 */ size()91 size_t size() { 92 std::scoped_lock lock(mLock); 93 return mQueue.size(); 94 } 95 96 private: 97 const size_t mCapacity; 98 /** 99 * Used to signal that mQueue is non-empty. 100 */ 101 std::condition_variable mHasElements; 102 /** 103 * Lock for accessing and waiting on elements. 104 */ 105 std::mutex mLock; 106 std::vector<T> mQueue GUARDED_BY(mLock); 107 }; 108 109 110 } // namespace android 111 #endif 112