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Siarhei Vishniakou473174e2017-12-27 16:44:42 -08001/*
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
Siarhei Vishniakou61291d42019-02-11 18:13:20 -080020#include "android-base/thread_annotations.h"
Siarhei Vishniakou473174e2017-12-27 16:44:42 -080021#include <condition_variable>
22#include <mutex>
23#include <vector>
24
25namespace 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 */
34template <class T>
35class BlockingQueue {
36public:
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 */
45 T pop() {
Siarhei Vishniakou443ad902019-03-06 17:25:41 -080046 std::unique_lock lock(mLock);
Siarhei Vishniakou61291d42019-02-11 18:13:20 -080047 android::base::ScopedLockAssertion assumeLock(mLock);
Siarhei Vishniakoue3021d72020-02-28 15:25:41 -080048 mHasElements.wait(lock, [this]() REQUIRES(mLock) { return !this->mQueue.empty(); });
Siarhei Vishniakou473174e2017-12-27 16:44:42 -080049 T t = std::move(mQueue.front());
50 mQueue.erase(mQueue.begin());
Siarhei Vishniakou61291d42019-02-11 18:13:20 -080051 return t;
Siarhei Vishniakou473174e2017-12-27 16:44:42 -080052 };
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 */
60 bool push(T&& t) {
Siarhei Vishniakou61291d42019-02-11 18:13:20 -080061 {
62 std::scoped_lock lock(mLock);
63 if (mQueue.size() == mCapacity) {
64 return false;
65 }
66 mQueue.push_back(std::move(t));
Siarhei Vishniakou473174e2017-12-27 16:44:42 -080067 }
Siarhei Vishniakou473174e2017-12-27 16:44:42 -080068 mHasElements.notify_one();
69 return true;
70 };
71
72 void erase(const std::function<bool(const T&)>& lambda) {
Siarhei Vishniakou61291d42019-02-11 18:13:20 -080073 std::scoped_lock lock(mLock);
Siarhei Vishniakouf47c339e2021-12-30 11:22:26 -080074 std::erase_if(mQueue, [&lambda](const auto& t) { return lambda(t); });
Siarhei Vishniakou473174e2017-12-27 16:44:42 -080075 }
76
77 /**
78 * Remove all elements.
79 * Does not block.
80 */
81 void clear() {
82 std::scoped_lock lock(mLock);
83 mQueue.clear();
84 };
85
Siarhei Vishniakoua028c442019-02-04 14:33:23 -080086 /**
87 * How many elements are currently stored in the queue.
88 * Primary used for debugging.
89 * Does not block.
90 */
91 size_t size() {
92 std::scoped_lock lock(mLock);
93 return mQueue.size();
94 }
95
Siarhei Vishniakou473174e2017-12-27 16:44:42 -080096private:
Siarhei Vishniakou61291d42019-02-11 18:13:20 -080097 const size_t mCapacity;
Siarhei Vishniakou473174e2017-12-27 16:44:42 -080098 /**
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;
Siarhei Vishniakou61291d42019-02-11 18:13:20 -0800106 std::vector<T> mQueue GUARDED_BY(mLock);
Siarhei Vishniakou473174e2017-12-27 16:44:42 -0800107};
108
109
110} // namespace android
111#endif