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      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