Fix locking for mMasterVolume and mMute

mMasterVolume and mMute are both protected by mutex in AudioFlinger class, but
there were two places where they were accessed without a mutex.

Also make AudioFlinger::mMasterMute private not protected.

Change-Id: Ia3897daeb5c50313df5bcc071824357526237f3e

services/audioflinger/AudioFlinger.cpp

@@ -646,12 +646,14 @@ status_t AudioFlinger::setMasterMute(bool muted)
 
 float AudioFlinger::masterVolume() const
 {
-    return mMasterVolume;
+    Mutex::Autolock _l(mLock);
+    return masterVolume_l();
 }
 
 bool AudioFlinger::masterMute() const
 {
-    return mMasterMute;
+    Mutex::Autolock _l(mLock);
+    return masterMute_l();
 }
 
 status_t AudioFlinger::setStreamVolume(int stream, float value, int output)
@@ -1379,8 +1381,10 @@ AudioFlinger::PlaybackThread::PlaybackThread(const sp<AudioFlinger>& audioFlinge
 
     readOutputParameters();
 
-    mMasterVolume = mAudioFlinger->masterVolume();
-    mMasterMute = mAudioFlinger->masterMute();
+    // Assumes constructor is called by AudioFlinger with it's mLock held,
+    // but it would be safer to explicitly pass these as parameters
+    mMasterVolume = mAudioFlinger->masterVolume_l();
+    mMasterMute = mAudioFlinger->masterMute_l();
 
     for (int stream = 0; stream < AUDIO_STREAM_CNT; stream++) {
         mStreamTypes[stream].volume = mAudioFlinger->streamVolumeInternal(stream);

services/audioflinger/AudioFlinger.h

@@ -765,7 +765,9 @@ private:
         int16_t*                        mMixBuffer;
         int                             mSuspended;
         int                             mBytesWritten;
+    private:
         bool                            mMasterMute;
+    protected:
         SortedVector< wp<Track> >       mActiveTracks;
 
         virtual int             getTrackName_l() = 0;
@@ -1388,6 +1390,8 @@ mutable Mutex               mLock;      // mutex for process, commands and handl
 
                 DefaultKeyedVector< int, sp<PlaybackThread> >  mPlaybackThreads;
                 PlaybackThread::stream_type_t       mStreamTypes[AUDIO_STREAM_CNT];
+
+                // both are protected by mLock
                 float                               mMasterVolume;
                 bool                                mMasterMute;
 
@@ -1399,6 +1403,9 @@ mutable Mutex               mLock;      // mutex for process, commands and handl
                 bool                                mBtNrecIsOff;
 
                 Vector<AudioSessionRef*> mAudioSessionRefs;
+
+                float       masterVolume_l() const  { return mMasterVolume; }
+                bool        masterMute_l() const    { return mMasterMute; }
 };