WaveTrack.cpp does not depend on ODManager.cpp ...

... Breaking up an s.c.c. of 6 into 3 components:
ODManager, ODTask, ODWaveTrackTaskQueue
UndoManager
WaveClip, WaveTrack

Rewrite the OD tasks and queues to hold weak pointers to tracks, so the
track destructor need not notify them.

src/ProjectFileManager.cpp

@@ -210,7 +210,7 @@ void ProjectFileManager::EnqueueODTasks()
          //add the track to the already created tasks that correspond to the od flags in the wavetrack.
          for(unsigned int i=0;i<newTasks.size();i++) {
             if(newTasks[i]->GetODType() & odFlags)
-               newTasks[i]->AddWaveTrack(wt);
+               newTasks[i]->AddWaveTrack(wt->SharedPointer< WaveTrack >());
          }
 
          //create whatever NEW tasks we need to.
@@ -236,7 +236,7 @@ void ProjectFileManager::EnqueueODTasks()
             }
             if(newTask)
             {
-               newTask->AddWaveTrack(wt);
+               newTask->AddWaveTrack(wt->SharedPointer< WaveTrack >());
                newTasks.push_back(std::move(newTask));
             }
          }

src/ProjectHistory.cpp

@@ -17,6 +17,7 @@ Paul Licameli split from ProjectManager.cpp
 #include "Track.h"
 #include "UndoManager.h"
 #include "ViewInfo.h"
+#include "WaveTrack.h"
 #include "ondemand/ODComputeSummaryTask.h"
 #include "ondemand/ODManager.h"
 
@@ -167,7 +168,7 @@ void ProjectHistory::PopState(const UndoState &state)
             // PRL:  Is it correct to add all tracks to one task, even if they
             // are not partnered channels?  Rather than
             // make one task for each?
-            computeTask->AddWaveTrack(wt);
+            computeTask->AddWaveTrack(wt->SharedPointer< WaveTrack >());
          }
       });
    }

src/WaveTrack.cpp

@@ -53,8 +53,6 @@ Track classes.
 
 #include "Prefs.h"
 
-#include "ondemand/ODManager.h"
-
 #include "effects/TimeWarper.h"
 #include "prefs/SpectrogramSettings.h"
 #include "prefs/TracksPrefs.h"
@@ -213,10 +211,6 @@ void WaveTrack::Merge(const Track &orig)
 
 WaveTrack::~WaveTrack()
 {
-   //Let the ODManager know this WaveTrack is disappearing.
-   //Deschedules tasks associated with this track.
-   if(ODManager::IsInstanceCreated())
-      ODManager::Instance()->RemoveWaveTrack(this);
 }
 
 double WaveTrack::GetOffset() const

src/effects/Effect.cpp

@@ -2256,7 +2256,7 @@ void Effect::ReplaceProcessedTracks(const bool bGoodResult)
          // Swap the wavecache track the ondemand task uses, since now the NEW
          // one will be kept in the project
          if (ODManager::IsInstanceCreated()) {
-            ODManager::Instance()->ReplaceWaveTrack( t, o.get() );
+            ODManager::Instance()->ReplaceWaveTrack( t, o );
          }
       }
    }

src/import/ImportFFmpeg.cpp

@@ -588,7 +588,7 @@ ProgressResult FFmpegImportFileHandle::Import(TrackFactory *trackFactory,
 
          //for each wavetrack within the stream add coded blockfiles
          for (int c = 0; c < sc->m_stream->codec->channels; c++) {
-            WaveTrack *t = stream[c].get();
+            auto t = stream[c];
             odTask->AddWaveTrack(t);
 
             auto maxBlockSize = t->GetMaxBlockSize();

src/import/ImportFLAC.cpp

@@ -505,7 +505,7 @@ ProgressResult FLACImportFileHandle::Import(TrackFactory *trackFactory,
       bool moreThanStereo = mNumChannels>2;
       for (const auto &channel : mChannels)
       {
-         mDecoderTask->AddWaveTrack(channel.get());
+         mDecoderTask->AddWaveTrack(channel);
          if(moreThanStereo)
          {
             //if we have 3 more channels, they get imported on seperate tracks, so we add individual tasks for each.

src/import/ImportPCM.cpp

@@ -445,7 +445,7 @@ ProgressResult PCMImportFileHandle::Import(TrackFactory *trackFactory,
          bool moreThanStereo = mInfo.channels>2;
          for (const auto &channel : channels)
          {
-            computeTask->AddWaveTrack(channel.get());
+            computeTask->AddWaveTrack(channel);
             if(moreThanStereo)
             {
                //if we have 3 more channels, they get imported on seperate tracks, so we add individual tasks for each.

src/ondemand/ODComputeSummaryTask.cpp

@@ -116,8 +116,9 @@ void ODComputeSummaryTask::DoSomeInternal()
          mWaveTrackMutex.Lock();
          for(size_t i=0;i<mWaveTracks.size();i++)
          {
-            if(success && mWaveTracks[i])
+            auto waveTrack = mWaveTracks[i].lock();
-               mWaveTracks[i]->AddInvalidRegion(blockStartSample,blockEndSample);
+            if(success && waveTrack)
+               waveTrack->AddInvalidRegion(blockStartSample,blockEndSample);
          }
          mWaveTrackMutex.Unlock();
       }
@@ -182,13 +183,14 @@ void ODComputeSummaryTask::Update()
 
    for(size_t j=0;j<mWaveTracks.size();j++)
    {
-      if(mWaveTracks[j])
+      auto waveTrack = mWaveTracks[j].lock();
+      if(waveTrack)
       {
          BlockArray *blocks;
          Sequence *seq;
 
          //gather all the blockfiles that we should process in the wavetrack.
-         for (const auto &clip : mWaveTracks[j]->GetAllClips()) {
+         for (const auto &clip : waveTrack->GetAllClips()) {
             seq = clip->GetSequence();
             //This lock may be way too big since the whole file is one sequence.
             //TODO: test for large files and find a way to break it down.

src/ondemand/ODDecodeTask.cpp

@@ -102,8 +102,9 @@ void ODDecodeTask::DoSomeInternal()
          mWaveTrackMutex.Lock();
          for(size_t i=0;i<mWaveTracks.size();i++)
          {
-            if(mWaveTracks[i])
+            auto waveTrack = mWaveTracks[i].lock();
-               mWaveTracks[i]->AddInvalidRegion(blockStartSample,blockEndSample);
+            if(waveTrack)
+               waveTrack->AddInvalidRegion(blockStartSample,blockEndSample);
          }
          mWaveTrackMutex.Unlock();
       }
@@ -138,13 +139,14 @@ void ODDecodeTask::Update()
 
    for(size_t j=0;j<mWaveTracks.size();j++)
    {
-      if(mWaveTracks[j])
+      auto waveTrack = mWaveTracks[j].lock();
+      if(waveTrack)
       {
          BlockArray *blocks;
          Sequence *seq;
 
          //gather all the blockfiles that we should process in the wavetrack.
-         for (const auto &clip : mWaveTracks[j]->GetAllClips()) {
+         for (const auto &clip : waveTrack->GetAllClips()) {
             seq = clip->GetSequence();
             //TODO:this lock is way to big since the whole file is one sequence.  find a way to break it down.
             seq->LockDeleteUpdateMutex();

src/ondemand/ODManager.cpp

@@ -257,7 +257,7 @@ void ODManager::AddNewTask(std::unique_ptr<ODTask> &&mtask, bool lockMutex)
    {
       //search for a task containing the lead track.  wavetrack removal is threadsafe and bound to the mQueuesMutex
       //note that GetWaveTrack is not threadsafe, but we are assuming task is not running on a different thread yet.
-      if(mQueues[i]->ContainsWaveTrack(task->GetWaveTrack(0)))
+      if(mQueues[i]->ContainsWaveTrack(task->GetWaveTrack(0).get()))
          queue = mQueues[i].get();
    }
 
@@ -472,20 +472,9 @@ void ODManager::Quit()
    }
 }
 
-///removes a wavetrack and notifies its associated tasks to stop using its reference.
-void ODManager::RemoveWaveTrack(WaveTrack* track)
-{
-   mQueuesMutex.Lock();
-   for(unsigned int i=0;i<mQueues.size();i++)
-   {
-      if(mQueues[i]->ContainsWaveTrack(track))
-         mQueues[i]->RemoveWaveTrack(track);
-   }
-   mQueuesMutex.Unlock();
-}
-
 ///replace the wavetrack whose wavecache the gui watches for updates
-void ODManager::ReplaceWaveTrack(Track *oldTrack, Track *newTrack)
+void ODManager::ReplaceWaveTrack(Track *oldTrack,
+   const std::shared_ptr<Track> &newTrack)
 {
    mQueuesMutex.Lock();
    for(unsigned int i=0;i<mQueues.size();i++)
@@ -496,13 +485,14 @@ void ODManager::ReplaceWaveTrack(Track *oldTrack, Track *newTrack)
 }
 
 ///if it shares a queue/task, creates a NEW queue/task for the track, and removes it from any previously existing tasks.
-void ODManager::MakeWaveTrackIndependent(WaveTrack* track)
+void ODManager::MakeWaveTrackIndependent(
+   const std::shared_ptr< WaveTrack > &track)
 {
    ODWaveTrackTaskQueue* owner=NULL;
    mQueuesMutex.Lock();
    for(unsigned int i=0;i<mQueues.size();i++)
    {
-      if(mQueues[i]->ContainsWaveTrack(track))
+      if(mQueues[i]->ContainsWaveTrack(track.get()))
       {
          owner = mQueues[i].get();
          break;
@@ -519,7 +509,10 @@ void ODManager::MakeWaveTrackIndependent(WaveTrack* track)
 ///better design in the future.
 ///@return returns success.  Some ODTask conditions require that the tasks finish before merging.
 ///e.g. they have different effects being processed at the same time.
-bool ODManager::MakeWaveTrackDependent(WaveTrack* dependentTrack,WaveTrack* masterTrack)
+bool ODManager::MakeWaveTrackDependent(
+   const std::shared_ptr< WaveTrack > &dependentTrack,
+   WaveTrack* masterTrack
+)
 {
    //First, check to see if the task lists are mergeable.  If so, we can simply add this track to the other task and queue,
    //then DELETE this one.
@@ -535,7 +528,7 @@ bool ODManager::MakeWaveTrackDependent(WaveTrack* dependentTrack,WaveTrack* mast
       {
          masterQueue = mQueues[i].get();
       }
-      else if(mQueues[i]->ContainsWaveTrack(dependentTrack))
+      else if(mQueues[i]->ContainsWaveTrack(dependentTrack.get()))
       {
          dependentQueue = mQueues[i].get();
          dependentIndex = i;

src/ondemand/ODManager.h

@@ -67,19 +67,20 @@ class ODManager final
    ///Wakes the queue loop up by signalling its condition variable.
    void SignalTaskQueueLoop();
 
-   ///removes a wavetrack and notifies its associated tasks to stop using its reference.
-   void RemoveWaveTrack(WaveTrack* track);
-
    ///if it shares a queue/task, creates a NEW queue/task for the track, and removes it from any previously existing tasks.
-   void MakeWaveTrackIndependent(WaveTrack* track);
+   void MakeWaveTrackIndependent( const std::shared_ptr< WaveTrack > &track);
 
    ///attach the track in question to another, already existing track's queues and tasks.  Remove the task/tracks.
    ///Returns success if it was possible..  Some ODTask conditions make it impossible until the Tasks finish.
-   bool MakeWaveTrackDependent(WaveTrack* dependentTrack,WaveTrack* masterTrack);
+   bool MakeWaveTrackDependent(
+      const std::shared_ptr< WaveTrack > &dependentTrack,
+      WaveTrack* masterTrack
+   );
 
    ///if oldTrack is being watched,
    ///replace the wavetrack whose wavecache the gui watches for updates
-   void ReplaceWaveTrack(Track *oldTrack, Track *newTrack);
+   void ReplaceWaveTrack(Track *oldTrack,
+      const std::shared_ptr< Track > &newTrack);
 
    ///Adds a task to the running queue.  Threas-safe.
    void AddTask(ODTask* task);

src/ondemand/ODTask.cpp

@@ -182,7 +182,7 @@ bool ODTask::IsTaskAssociatedWithProject(AudacityProject* proj)
       mWaveTrackMutex.Lock();
       for(int i=0;i<(int)mWaveTracks.size();i++)
       {
-         if(mWaveTracks[i]==tr)
+         if ( mWaveTracks[i].lock().get() == tr )
          {
             //if we find one, then the project is associated with us;return true
             mWaveTrackMutex.Unlock();
@@ -252,19 +252,19 @@ bool ODTask::IsComplete()
 }
 
 
-WaveTrack* ODTask::GetWaveTrack(int i)
+std::shared_ptr< WaveTrack > ODTask::GetWaveTrack(int i)
 {
-   WaveTrack* track = NULL;
+   std::shared_ptr< WaveTrack > track;
    mWaveTrackMutex.Lock();
    if(i<(int)mWaveTracks.size())
-      track = mWaveTracks[i];
+      track = mWaveTracks[i].lock();
    mWaveTrackMutex.Unlock();
    return track;
 }
 
 ///Sets the wavetrack that will be analyzed for ODPCMAliasBlockFiles that will
 ///have their summaries computed and written to disk.
-void ODTask::AddWaveTrack(WaveTrack* track)
+void ODTask::AddWaveTrack( const std::shared_ptr< WaveTrack > &track)
 {
    mWaveTracks.push_back(track);
 }
@@ -321,7 +321,7 @@ void ODTask::DemandTrackUpdate(WaveTrack* track, double seconds)
    mWaveTrackMutex.Lock();
    for(size_t i=0;i<mWaveTracks.size();i++)
    {
-      if(track == mWaveTracks[i])
+      if ( track == mWaveTracks[i].lock().get() )
       {
          auto newDemandSample = (sampleCount)(seconds * track->GetRate());
          demandSampleChanged = newDemandSample != GetDemandSample();
@@ -342,21 +342,22 @@ void ODTask::StopUsingWaveTrack(WaveTrack* track)
    mWaveTrackMutex.Lock();
    for(size_t i=0;i<mWaveTracks.size();i++)
    {
-      if(mWaveTracks[i] == track)
+      if(mWaveTracks[i].lock().get() == track)
-         mWaveTracks[i]=NULL;
+         mWaveTracks[i].reset();
    }
    mWaveTrackMutex.Unlock();
 }
 
 ///Replaces all instances to a wavetrack with a NEW one, effectively transferring the task.
-void ODTask::ReplaceWaveTrack(Track *oldTrack, Track *newTrack)
+void ODTask::ReplaceWaveTrack(Track *oldTrack,
+   const std::shared_ptr< Track > &newTrack)
 {
    mWaveTrackMutex.Lock();
    for(size_t i=0;i<mWaveTracks.size();i++)
    {
-      if(oldTrack == mWaveTracks[i])
+      if(oldTrack == mWaveTracks[i].lock().get())
       {
-         mWaveTracks[i] = static_cast<WaveTrack*>( newTrack );
+         mWaveTracks[i] = std::static_pointer_cast<WaveTrack>( newTrack );
       }
    }
    mWaveTrackMutex.Unlock();

src/ondemand/ODTask.h

@@ -84,12 +84,13 @@ class ODTask /* not final */
 
    ///Replaces all instances to a wavetrack with a NEW one, effectively transferring the task.
    ///ODTask has no wavetrack, so it does nothing.  But subclasses that do should override this.
-   virtual void ReplaceWaveTrack(Track *oldTrack, Track *newTrack);
+   virtual void ReplaceWaveTrack(Track *oldTrack,
+      const std::shared_ptr< Track > &newTrack);
 
     ///Adds a WaveTrack to do the task for
-   void AddWaveTrack(WaveTrack* track);
+   void AddWaveTrack( const std::shared_ptr< WaveTrack > &track);
    virtual int GetNumWaveTracks();
-   virtual WaveTrack* GetWaveTrack(int i);
+   virtual std::shared_ptr< WaveTrack > GetWaveTrack(int i);
 
    ///changes the tasks associated with this Waveform to process the task from a different point in the track
    virtual void DemandTrackUpdate(WaveTrack* track, double seconds);
@@ -156,7 +157,7 @@ class ODTask /* not final */
    //for a function not a member var.
    ODLock mBlockUntilTerminateMutex;
 
-   std::vector<WaveTrack*> mWaveTracks;
+   std::vector< std::weak_ptr< WaveTrack > > mWaveTracks;
    ODLock     mWaveTrackMutex;
 
    sampleCount mDemandSample;

src/ondemand/ODWaveTrackTaskQueue.cpp

@@ -64,7 +64,8 @@ bool ODWaveTrackTaskQueue::CanMergeWith(ODWaveTrackTaskQueue* otherQueue)
 /// sets the NeedODUpdateFlag since we don't want the head task to finish without haven't dealt with the depednent
 ///
 ///@param track the track to bring into the tasks AND tracklist for this queue
-void ODWaveTrackTaskQueue::MergeWaveTrack(WaveTrack* track)
+void ODWaveTrackTaskQueue::MergeWaveTrack(
+   const std::shared_ptr< WaveTrack > &track)
 {
    AddWaveTrack(track);
    mTasksMutex.Lock();
@@ -83,7 +84,7 @@ bool ODWaveTrackTaskQueue::ContainsWaveTrack(const WaveTrack* track)
    mTracksMutex.Lock();
    for(unsigned int i=0;i<mTracks.size();i++)
    {
-      if(mTracks[i]==track)
+      if ( mTracks[i].lock().get() == track )
       {
          mTracksMutex.Unlock();
          return true;
@@ -93,7 +94,8 @@ bool ODWaveTrackTaskQueue::ContainsWaveTrack(const WaveTrack* track)
    return false;
 }
 ///Adds a track to the associated list.
-void ODWaveTrackTaskQueue::AddWaveTrack(WaveTrack* track)
+void ODWaveTrackTaskQueue::AddWaveTrack(
+   const std::shared_ptr< WaveTrack > &track)
 {
 
    mTracksMutex.Lock();
@@ -117,8 +119,7 @@ void ODWaveTrackTaskQueue::AddTask(std::unique_ptr<ODTask> &&mtask)
    {
       //task->GetWaveTrack(i) may return NULL, but we handle it by checking before using.
       //The other worry that the WaveTrack returned and was deleted in the meantime is also
-      //handled since mQueuesMutex is locked one up in the stack from here,
+      //handled by keeping standard weak pointers to tracks, which give thread safety.
-      //and WaveTrack deletion is bound to that.
       mTracks.push_back(task->GetWaveTrack(i));
    }
 
@@ -126,32 +127,15 @@ void ODWaveTrackTaskQueue::AddTask(std::unique_ptr<ODTask> &&mtask)
 
 }
 
-///Removes a track from the list.  Also notifies mTasks to stop using references
-///to the instance in a thread-safe manner (may block)
-void ODWaveTrackTaskQueue::RemoveWaveTrack(WaveTrack* track)
-{
-   if(track)
-   {
-
-      mTasksMutex.Lock();
-      for(unsigned int i=0;i<mTasks.size();i++)
-         mTasks[i]->StopUsingWaveTrack(track);
-      mTasksMutex.Unlock();
-
-      mTracksMutex.Lock();
-      for(unsigned int i=0;i<mTracks.size();i++)
-         if(mTracks[i]==track)
-            mTracks.erase(mTracks.begin()+i--);//decrement i after the removal.
-
-      mTracksMutex.Unlock();
-   }
-}
-
 //if the wavetrack is in this queue, and is not the only wavetrack, clones the tasks and schedules it.
-void ODWaveTrackTaskQueue::MakeWaveTrackIndependent(WaveTrack* track)
+void ODWaveTrackTaskQueue::MakeWaveTrackIndependent(
+   const std::shared_ptr< WaveTrack > &track)
 {
+   // First remove expired weak pointers
+   Compress();
    
    mTracksMutex.Lock();
+
    if(mTracks.size()<2)
    {
       //if there is only one track, it is already independent.
@@ -161,17 +145,16 @@ void ODWaveTrackTaskQueue::MakeWaveTrackIndependent(WaveTrack* track)
 
    for(unsigned int i=0;i<mTracks.size();i++)
    {
-      if(mTracks[i]==track)
+      if ( mTracks[i].lock() == track )
       {
-         mTracksMutex.Unlock();//release the lock, since RemoveWaveTrack is a public threadsafe method.
+         mTracks[i].reset();
-         RemoveWaveTrack(mTracks[i]);
 
          //clone the items in order and add them to the ODManager.
          mTasksMutex.Lock();
          for(unsigned int j=0;j<mTasks.size();j++)
          {
             auto task = mTasks[j]->Clone();
-            task->AddWaveTrack(track);
+            mTasks[j]->StopUsingWaveTrack( track.get() );
             //AddNewTask requires us to relinquish this lock. However, it is safe because ODManager::MakeWaveTrackIndependent
             //has already locked the m_queuesMutex.
             mTasksMutex.Unlock();
@@ -181,7 +164,6 @@ void ODWaveTrackTaskQueue::MakeWaveTrackIndependent(WaveTrack* track)
             mTasksMutex.Lock();
          }
          mTasksMutex.Unlock();
-         mTracksMutex.Lock();
          break;
       }
    }
@@ -207,7 +189,8 @@ void ODWaveTrackTaskQueue::DemandTrackUpdate(WaveTrack* track, double seconds)
 
 
 //Replaces all instances of a wavetracck with a NEW one (effectively transferes the task.)
-void ODWaveTrackTaskQueue::ReplaceWaveTrack(Track *oldTrack, Track *newTrack)
+void ODWaveTrackTaskQueue::ReplaceWaveTrack(Track *oldTrack,
+   const std::shared_ptr<Track> &newTrack)
 {
    if(oldTrack)
    {
@@ -218,26 +201,17 @@ void ODWaveTrackTaskQueue::ReplaceWaveTrack(Track *oldTrack, Track *newTrack)
 
       mTracksMutex.Lock();
       for(unsigned int i=0;i<mTracks.size();i++)
-         if(mTracks[i]==oldTrack)
+         if ( mTracks[i].lock().get() == oldTrack )
-            mTracks[i] = static_cast<WaveTrack*>( newTrack );
+            mTracks[i] = std::static_pointer_cast<WaveTrack>( newTrack );
       mTracksMutex.Unlock();
    }
 }
 
-//returns the wavetrack at position x.
-WaveTrack* ODWaveTrackTaskQueue::GetWaveTrack(size_t x)
-{
-   WaveTrack* ret = NULL;
-   mTracksMutex.Lock();
-   if (x < mTracks.size())
-      ret = mTracks[x];
-   mTracksMutex.Unlock();
-   return ret;
-}
-
 ///returns the number of wavetracks in this queue.
 int ODWaveTrackTaskQueue::GetNumWaveTracks()
 {
+   Compress();
+
    int ret = 0;
    mTracksMutex.Lock();
    ret=mTracks.size();
@@ -271,6 +245,8 @@ ODTask* ODWaveTrackTaskQueue::GetTask(size_t x)
 //returns true if either tracks or tasks are empty
 bool ODWaveTrackTaskQueue::IsEmpty()
 {
+   Compress();
+
    bool isEmpty;
    mTracksMutex.Lock();
    isEmpty = mTracks.size()<=0;
@@ -342,3 +318,13 @@ void ODWaveTrackTaskQueue::FillTipForWaveTrack( const WaveTrack * t, wxString &t
 
    }
 }
+
+void ODWaveTrackTaskQueue::Compress()
+{
+   mTracksMutex.Lock();
+   auto begin = mTracks.begin(), end = mTracks.end(),
+   new_end = std::remove_if( begin, end,
+      []( const std::weak_ptr<WaveTrack> &ptr ){ return ptr.expired(); } );
+   mTracks.erase( new_end, end );
+   mTracksMutex.Unlock();
+}

src/ondemand/ODWaveTrackTaskQueue.h

@@ -42,31 +42,26 @@ class ODWaveTrackTaskQueue final
 
 
    ///Adds a track to the associated list.
-   void AddWaveTrack(WaveTrack* track);
+   void AddWaveTrack( const std::shared_ptr< WaveTrack > &track);
-   ///Removes a track from the list.  Also notifies mTasks to stop using references
-   ///to the instance in a thread-safe manner (may block)
-   void RemoveWaveTrack(WaveTrack* track);
 
    ///changes the tasks associated with this Waveform to process the task from a different point in the track
    void DemandTrackUpdate(WaveTrack* track, double seconds);
 
    ///replaces all instances of a WaveTrack within this task with another.
-   void ReplaceWaveTrack(Track *oldTrack, Track *newTrack);
+   void ReplaceWaveTrack(Track *oldTrack,
+      const std::shared_ptr<Track> &newTrack);
 
    //if the wavetrack is in this queue, and is not the only wavetrack, clones the tasks and schedules it.
-   void MakeWaveTrackIndependent(WaveTrack* track);
+   void MakeWaveTrackIndependent( const std::shared_ptr< WaveTrack > &track);
 
    ///returns whether or not this queue's task list and another's can merge together, as when we make two mono tracks stereo.
    bool CanMergeWith(ODWaveTrackTaskQueue* otherQueue);
-   void MergeWaveTrack(WaveTrack* track);
+   void MergeWaveTrack( const std::shared_ptr< WaveTrack > &track);
 
 
    //returns true if the agrument is in the WaveTrack list.
    bool ContainsWaveTrack(const WaveTrack* track);
 
-   //returns the wavetrack at position x.
-   WaveTrack* GetWaveTrack(size_t x);
-
    ///returns the number of wavetracks in this queue.
    int GetNumWaveTracks();
 
@@ -96,12 +91,15 @@ class ODWaveTrackTaskQueue final
 
  protected:
 
+   // Remove expired weak pointers to tracks
+   void Compress();
+
    //because we need to save this around for the tool tip.
    wxString mTipMsg;
 
 
   ///the list of tracks associated with this queue.
-  std::vector<WaveTrack*> mTracks;
+  std::vector< std::weak_ptr< WaveTrack > > mTracks;
   ODLock mTracksMutex;
 
   ///the list of tasks associated with the tracks.  This class owns these tasks.

src/tracks/playabletrack/wavetrack/ui/WaveTrackControls.cpp

@@ -889,7 +889,8 @@ void WaveTrackMenuTable::OnMergeStereo(wxCommandEvent &)
 
    //On Demand - join the queues together.
    if (ODManager::IsInstanceCreated())
-      if (!ODManager::Instance()->MakeWaveTrackDependent(partner, pTrack))
+      if (!ODManager::Instance()
+         ->MakeWaveTrackDependent(partner->SharedPointer<WaveTrack>(), pTrack))
       {
          ;
          //TODO: in the future, we will have to check the return value of MakeWaveTrackDependent -
@@ -927,7 +928,8 @@ void WaveTrackMenuTable::SplitStereo(bool stereo)
 
       //On Demand - have each channel add its own.
       if (ODManager::IsInstanceCreated())
-         ODManager::Instance()->MakeWaveTrackIndependent(channel);
+         ODManager::Instance()->MakeWaveTrackIndependent(
+            channel->SharedPointer<WaveTrack>() );
       //make sure no channel is smaller than its minimum height
       if (view.GetHeight() < view.GetMinimizedHeight())
          view.SetHeight(view.GetMinimizedHeight());