1 /*
2  * Copyright (C) 2011 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 #include "utils/threads.h"
18 
19 //--------------------------------------------------------------------------------------------------
20 namespace android {
21 
22 class CallbackProtector : public RefBase {
23 
24 public:
25     CallbackProtector();
26     virtual ~CallbackProtector();
27 
28     /**
29      * Indicates whether the CallbackProtector is non-NULL and it's safe to enter the callback.
30      */
31     static bool enterCbIfOk(const sp<CallbackProtector> &protector);
32 
33     /**
34      * Indicates whether it's safe to enter the callback. It would typically return false
35      * if the associated object (AudioTrack, AudioPlayer, MediaPlayer) is about to be destroyed.
36      */
37     bool enterCb();
38 
39     /**
40      * This method must be paired to each call to enterCb() or enterCbIfOk(),
41      * only it returned that it is safe enter the callback;
42      */
43     void exitCb();
44 
45     /**
46      * Called to signal the associated object is about to be destroyed, so whenever a callback is
47      * entered (see enterCb) it will be notified it is pointless to process the callback. This will
48      * return immediately if there are no callbacks, and will block until current callbacks exit.
49      */
50     void requestCbExitAndWait();
51 
52     /**
53      * Similar to requestCbExitAndWait, but does not wait for current callbacks to exit.
54      */
55     void requestCbExit();
56 
57 private:
58     Mutex mLock;
59     Condition mCbExitedCondition;
60 
61     bool mSafeToEnterCb;
62 
63     /** Counts the number of callbacks actively locking the associated AudioPlayer */
64     unsigned int mCbCount;
65 
66 #ifdef USE_DEBUG
67     pthread_t mCallbackThread;
68     pid_t mCallbackTid;
69     pthread_t mRequesterThread;
70     pid_t mRequesterTid;
71 #endif
72 
73     // disallow "evil" constructors
74     CallbackProtector(const CallbackProtector &);
75     CallbackProtector &operator=(const CallbackProtector &);
76 };
77 
78 } // namespace android
79