Singleton Class and "Leaked objects detected"

General JUCE discussion
1

Hi I created this class to manage the structure of my application (obviously this is an extract of my class, for example I converted in string a lot of identifiers and I remove a lot of methods to simplify the code to post here):

enum ChType {audio, midi, input, send, cue};

class RootEngine {
public:
    
    UndoManager undoManager{};
    
    ValueTree rootVt {"root"};
    
    ValueTree channelsVt {"channels"};
    ValueTree inputsVt {"inputs"};
    ValueTree sendsVt {"sends"};
    ValueTree cuesVt {"cues"};
    ValueTree mainOutVt {"mainOut"};
    ValueTree clockVt {"clock"};
    
    static RootEngine* sharedInstance()
    {
        static RootEngine rootEngine;
        return &rootEngine;
    }
    
    
    void addChannel(String chName, int chIndex, ChType type)
    {
        undoManager.beginNewTransaction();
        
        ValueTree channelVt;
        
        switch (type) {
            case audio:
                channelVt = ValueTree{"aucioCh"};
                channelsVt.addChild(channelVt, -1, &undoManager);
                break;
                
            case midi:
                channelVt = ValueTree{"instrCh"};
                channelsVt.addChild(channelVt, -1, &undoManager);
                break;
                
            case input:
                channelVt = ValueTree{"inputCh"};
                inputsVt.addChild(channelVt, -1, &undoManager);
                break;
                
            case send:
                channelVt = ValueTree{"sendCh"};
                sendsVt.addChild(channelVt, -1, &undoManager);
                break;
                
            case cue:
                channelVt = ValueTree{"cueCh"};
                cuesVt.addChild(channelVt, -1, &undoManager);
                break;
                
        }
    }
    
    ScopedPointer<XmlElement> createRootXml()
    {
        ScopedPointer<XmlElement> xml = rootVt.createXml();
        return xml;
    }
    
    ~RootEngine() {}
    
private:
    
    RootEngine()
    {
        
        rootVt.addChild(channelsVt, -1, nullptr);
        rootVt.addChild(inputsVt, -1, nullptr);
        rootVt.addChild(sendsVt, -1, nullptr);
        rootVt.addChild(cuesVt, -1, nullptr);
        rootVt.addChild(mainOutVt, -1, nullptr);
        rootVt.addChild(clockVt, -1, nullptr);
        
        rootVt.getChildWithName("mainOut").setProperty("volume", 0, nullptr);
        rootVt.getChildWithName("mainOut").setProperty("panpot", 0, nullptr);
        rootVt.getChildWithName("mainOut").setProperty("metroOn", false, nullptr);
        rootVt.getChildWithName("mainOut").setProperty("metroVolume", 0, nullptr);
        rootVt.getChildWithName("mainOut").setProperty("metroPanpot", 0, nullptr);
        rootVt.getChildWithName("clock").setProperty("bpm", 120, nullptr);
        rootVt.getChildWithName("clock").setProperty("movements", 4, nullptr);
    }
    
};

And in my MainComponent.cpp I created some buttons with this onClick method implementations:

addMidi.onClick = [this]()
{
    DBG("Inside addMidi:");
    RootEngine::sharedInstance()->addChannel("midiTrack" + String(++i), i, ChType::midi);
    
};
addAudio.onClick = [this]()
{
    DBG("Inside addAudio:");
    RootEngine::sharedInstance()->addChannel("audioTrack" + String(++i), i, ChType::audio);
};
addInput.onClick = [this]()
{
    DBG("Inside addInput:");
    RootEngine::sharedInstance()->addChannel("inputTrack" + String(++i), i, ChType::input);

};
addSend.onClick = [this]()
{
    DBG("Inside addInput:");
    RootEngine::sharedInstance()->addChannel("sendTrack" + String(++i), i, ChType::send);
};
addCue.onClick = [this]()
{
    DBG("Inside addInput:");
    RootEngine::sharedInstance()->addChannel("cueTrack" + String(++i), i, ChType::cue);
};
tb2.onClick = [this]()
{
    DBG("Inside undo:");
    RootEngine::sharedInstance()->undoManager.undo();
};
tb3.onClick = [this]()
{
    DBG("Inside redo:");
    RootEngine::sharedInstance()->undoManager.redo();
};
tb4.onClick = [this]()
{
    DBG("Inside print:");
    DBG(RootEngine::sharedInstance()->createRootXml()->createDocument(""));
};

All works but when I quit from my application on console come out this error:
***** Leaked objects detected: “X” instance(s) of class OwnedArray**
(“X” here is the number of channels added).

Someone can help me to understand whats going on here and how to solve this? Thank you in advice!

2

JUCE’s leak detector fires before static destructors are called. To get around this you can use JUCE’s singleton wrapper like so:

1 Like
3

@ t0m really thank you for your reply! I change my class as you show me with your post, so I:

  1. Delete this method:

     static RootEngine* sharedInstance()
 {
     static RootEngine rootEngine;
     return &rootEngine;
 }

  2. Inherited my class from DeletedAtShutdown adding " : private DeletedAtShutdown"

  3. Add this line inside the public: of my class: “JUCE_DECLARE_SINGLETON(RootEngine, false )”

  4. Add this line outside my class: “JUCE_IMPLEMENT_SINGLETON (RootEngine)”

  5. Add this line inside the destructor (I have both constructor and destructor of my class under private: section): “clearSingletonInstance();”

However when I try to compile my project xCode fails and gives me this error:
“linker command failed with exit code 1 (use -v to see invocation)”.

I’m sorry for the trouble and I really thank you again! :slight_smile:

4

Did you put this line into a cpp file? afaik it won’t work, if it’s in a header file.

1 Like
5

WOW thank you @daniel, now all works perfectly, but can I ask you why it doesn’t work if it is in the same .h file? (it’s just my curiosity) !

Really thank you again!

6

The static variable of your singleton needs to be initialised exactly one time. A header occurs in several translation units, so you will end up with multiple definitions.
By putting it into a cpp, it will be initialised in one translation unit, and the linker can find it when putting all together.

I know that it works that way, but the explanation might be not completely accurate. Anybody please correct me if I am wrong.

1 Like
7

Really Thank you again! :slight_smile:

8

The singleton macro stuff is probably one of the oldest surviving bits of JUCE… I think with C++14 it’s probably possible now to write something much cleaner and easier to use.

However, you might want to think about using juce::SharedResourcePointer instead, which cleans itself up automatically using reference counting.

2 Likes
9

Thank you! I’ll try it! :slight_smile: