1 /*
2  * Copyright 2021 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 <ftl/small_vector.h>
20 #include <semaphore.h>
21 #include <thread>
22 
23 #include "LocklessQueue.h"
24 
25 namespace android {
26 
27 // Executes tasks off the main thread.
28 class BackgroundExecutor {
29 public:
30     ~BackgroundExecutor();
31 
getInstance()32     static BackgroundExecutor& getInstance() {
33         static BackgroundExecutor instance(true);
34         return instance;
35     }
36 
getLowPriorityInstance()37     static BackgroundExecutor& getLowPriorityInstance() {
38         static BackgroundExecutor instance(false);
39         return instance;
40     }
41 
42     using Callbacks = ftl::SmallVector<std::function<void()>, 10>;
43     // Queues callbacks onto a work queue to be executed by a background thread.
44     // This is safe to call from multiple threads.
45     void sendCallbacks(Callbacks&& tasks);
46     void flushQueue();
47 
48 private:
49     BackgroundExecutor(bool highPriority);
50 
51     sem_t mSemaphore;
52     std::atomic_bool mDone = false;
53 
54     LocklessQueue<Callbacks> mCallbacksQueue;
55     std::thread mThread;
56 };
57 
58 } // namespace android
59