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]{ 49 android::base::ScopedLockAssertion assumeLock(mLock); 50 return !this->mQueue.empty(); 51 }); 52 T t = std::move(mQueue.front()); 53 mQueue.erase(mQueue.begin()); 54 return t; 55 }; 56 57 /** 58 * Add a new object to the queue. 59 * Does not block. 60 * Return true if an element was successfully added. 61 * Return false if the queue is full. 62 */ push(T && t)63 bool push(T&& t) { 64 { 65 std::scoped_lock lock(mLock); 66 if (mQueue.size() == mCapacity) { 67 return false; 68 } 69 mQueue.push_back(std::move(t)); 70 } 71 mHasElements.notify_one(); 72 return true; 73 }; 74 erase(const std::function<bool (const T &)> & lambda)75 void erase(const std::function<bool(const T&)>& lambda) { 76 std::scoped_lock lock(mLock); 77 mQueue.erase(std::remove_if(mQueue.begin(), mQueue.end(), 78 [&lambda](const T& t) { return lambda(t); }), mQueue.end()); 79 } 80 81 /** 82 * Remove all elements. 83 * Does not block. 84 */ clear()85 void clear() { 86 std::scoped_lock lock(mLock); 87 mQueue.clear(); 88 }; 89 90 /** 91 * How many elements are currently stored in the queue. 92 * Primary used for debugging. 93 * Does not block. 94 */ size()95 size_t size() { 96 std::scoped_lock lock(mLock); 97 return mQueue.size(); 98 } 99 100 private: 101 const size_t mCapacity; 102 /** 103 * Used to signal that mQueue is non-empty. 104 */ 105 std::condition_variable mHasElements; 106 /** 107 * Lock for accessing and waiting on elements. 108 */ 109 std::mutex mLock; 110 std::vector<T> mQueue GUARDED_BY(mLock); 111 }; 112 113 114 } // namespace android 115 #endif 116