1 /*
2  * Copyright (C) 2016 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 CHRE_EVENT_REF_QUEUE_H
18 #define CHRE_EVENT_REF_QUEUE_H
19 
20 #include "chre/core/event.h"
21 #include "chre/util/array_queue.h"
22 
23 namespace chre {
24 
25 /**
26  * A non-thread-safe, non-blocking wrapper around ArrayQueue that stores Event*
27  * and manages the Event reference counter.
28  * TODO: make this a template specialization? Or rework the ref count design?
29  */
30 class EventRefQueue {
31  public:
32   ~EventRefQueue();
33 
34   /**
35    * @return true if there are no events in the queue
36    */
empty()37   bool empty() const {
38     return mQueue.empty();
39   }
40 
41   /**
42    * Adds an event to the queue, and increments its reference counter
43    *
44    * @param event The event to add
45    * @return true on success
46    */
47   bool push(Event *event);
48 
49   /**
50    * Removes the oldest event from the queue, and decrements its reference
51    * counter. Does not trigger freeing of the event if the reference count
52    * reaches 0 as a result of this function call. The queue must be non-empty as
53    * a precondition to calling this function, or undefined behavior will result.
54    *
55    * @return Pointer to the next event in the queue
56    */
57   Event *pop();
58 
59  private:
60   //! The maximum number of events that can be outstanding for an app.
61   static constexpr size_t kMaxPendingEvents = 16;
62 
63   //! The queue of incoming events.
64   ArrayQueue<Event *, kMaxPendingEvents> mQueue;
65 };
66 
67 }  // namespace chre
68 
69 #endif  // CHRE_EVENT_REF_QUEUE_H
70