Panic USER 42: how it is here ???

[KhaledMahmood]

This very simple app to get cell ID raised Panic USER 42 on Exit. Pls help me to come out from this.

In the emulator the code shows Cell ID as 0, but while exiting it raises the panic: USER 42.
As USER 42 is abt heap cell pointer, I checked the code throughly, but can't trace any invalid pointer in the code that may cause this panic. I am using Visual Studio 2003 and Carbide 2.0.

Below the code is given

// CCellIDAppUi.cpp

void CCellIDAppUi::ConstructL()
    {
    // Initialise app UI with standard value.
    BaseConstructL();

    // Create view object
    iAppView = CCellIDAppView::NewL( ClientRect() );
	
    //Create Net Info retriever
    iNetInformer = CNetworkInfo::NewL();
    }
CCellIDAppUi::CCellIDAppUi()
    {
    // No implementation required
    }

CCellIDAppUi::~CCellIDAppUi()
    {
    if ( iAppView )
        {
        delete iAppView;
        iAppView = NULL;
        }

    if(iNetInformer)
	{
	delete iNetInformer;
	iNetInformer = NULL;
	}
    }

void CCellIDAppUi::HandleCommandL( TInt aCommand )
    {
    switch( aCommand )
        {
        case EEikCmdExit:
        case EAknSoftkeyExit:
            Exit();
            break;
        case ECellIDGetCellID:
            {
		iNetInformer->GetNetworkInfoL();
            }
            break;
        //default:
            //Panic( ECellIDUi );
            //break;
        }
    }

//NetworkInfo.h

#include <e32base.h>	// For CActive, link against: euser.lib
#include <etel3rdparty.h> // CTelephony, Link against etel3rdparty.lib

class CNetworkInfo : public CActive
{
public:
        static CNetworkInfo* NewL();
        ~CNetworkInfo();
        void GetNetworkInfoL();
 
    protected:
        // from CActive
        void RunL();
        TInt RunError(TInt aError);
        void DoCancel();
 
    private:
        CNetworkInfo();
        void ConstructL();
 
    private:
        CTelephony* iTelephony;
        CTelephony::TNetworkInfoV1 iNwInfo;
        CTelephony::TNetworkInfoV1Pckg iNwInfoPckg;
};

// NetworkInfo.cpp

#include <aknnotewrappers.h>
#include "NetworkInfo.h"

CNetworkInfo::CNetworkInfo()
    : CActive(EPriorityStandard),
      iNwInfoPckg(iNwInfo)
    {
    CActiveScheduler::Add(this);
    }
 
CNetworkInfo* CNetworkInfo::NewL()
    {
    CNetworkInfo* self = new (ELeave) CNetworkInfo;
    CleanupStack::PushL(self);
    self->ConstructL();
    CleanupStack::Pop();
    return self;
    }
 
void CNetworkInfo::ConstructL()
    {
    iTelephony = CTelephony::NewL();
    }
 
CNetworkInfo::~CNetworkInfo()
    {
    Cancel();
    delete iTelephony;
    }
 
// This function is used by our class' users to start getting network info.
void CNetworkInfo::GetNetworkInfoL()
    {
    __ASSERT_ALWAYS(!IsActive(), User::Leave(KErrInUse));
 
    // Start async call to receive current network information
    iTelephony->GetCurrentNetworkInfo(iStatus, iNwInfoPckg);
    SetActive();
    }
 
void CNetworkInfo::DoCancel()
    {
    iTelephony->CancelAsync(CTelephony::EGetCurrentNetworkInfoCancel);
    }
 
void CNetworkInfo::RunL()
    {
    User::LeaveIfError(iStatus.Int());
    // Request completed successfully.

    _LIT(KFormatter, "Current Cell ID is: %d");
    HBufC *msg = HBufC::NewLC(31);

    msg->Des().Format(KFormatter, iNwInfo.iCellId);

    CAknInformationNote* informationNote = new ( ELeave ) CAknInformationNote;
    informationNote->ExecuteLD( *msg );
    CleanupStack::PopAndDestroy(msg);
    }
 
TInt CNetworkInfo::RunError(TInt aError)
    {
    // There was an error retrieving current network info.
    
     _LIT(KFormatter, "CActive::RunError !!!");
     HBufC *msg = HBufC::NewLC(31);

     msg->Des().Format(KFormatter);

    CAknInformationNote* informationNote = new ( ELeave ) CAknInformationNote;
    informationNote->ExecuteLD( *msg );
    CleanupStack::PopAndDestroy(msg);
 
    return KErrNone;
    }

[sriky27]

Hi,

You could try logging and then check at this moment I cannot think of anything else.

[stenlik]

Hi,

I'm not 100% sure, but you delete in the CCellIDAppUi destructor the CNetworkInfo object, while in the CNetworkInfo destructor you call the Cancel() method, which calls CancelAsync() - as this is asynchronous cancel method - the result might be that OS tries to call the CNetworkInfo::RunL() to inform you that the cancel is complete, while the CNetworkInfo object was already deleted...

Regards,
STeN

[yogpan]

Hi,
I think StenLik is right .In the destructor of CNetworkInfo class you are directly calling the Cancel() without checking whether there is any request pending or not. It is always a good practice to check if there is any pending request before calling DoCancel() something like
if(IsActive())
{
Cancel();
}

[KhaledMahmood]

Cancel()

IMPORT_C void Cancel();

Description
Cancels the wait for completion of an outstanding request.

If there is no request outstanding, then the function does nothing.

If there is an outstanding request, the function:

1. calls the active object's DoCancel() function, provided by the derived class to implement cancellation of the request.

2. waits for the cancelled request to complete; this must complete as fast as possible.

3. marks the active object's request as complete (i.e. the request is no longer outstanding).

And this is the description taken from SDK Doc.

So how the problem could arise for Cancel() on destructor???

Regards.

[yogpan]

Hi,
Yes u are correct in the description. Thanks for pointing the fact. But the code which you have provided I am not able to figure out any other logical reason for the error. Are you working on emulator then you can try HookLogger to track the issue.

[ltomuta]

Yes, the documentation is correct, Cancel includes the check for IsActive internally.

However,stenlik is saying something entirely different, and that is that CancelAsync is a asynchronous call which will end-up triggering your RunL with a KErrCancel status. One would assume that only after receiving this notification the active object could in fact be deleted

[wizard_hu_]

You should also check that on a real device (enable the panic codes if you have not done so: http://wiki.forum.nokia.com/index.ph...ded_panic_code), telephony support in the emulator may have some problems.

[KhaledMahmood]

you delete in the CCellIDAppUi destructor the CNetworkInfo object, while in the CNetworkInfo destructor you call the Cancel() method, which calls CancelAsync() - as this is asynchronous cancel method - the result might be that OS tries to call the CNetworkInfo::RunL() to inform you that the cancel is complete, while the CNetworkInfo object was already deleted...

As told by Stenlik, do u think such situation may arise in my app where CancelAsync() isn't getting called when there are no outstanding request.

Thanks wizard_hu_ for the link.

Thanks all for ur prompt response. It’s really encouraging for new Symbian developers.

Regards.

[shixuehuiab]

Try this:

//CleanupStack::PopAndDestroy(msg);

[sumit.rathi]

Try this:

//CleanupStack::PopAndDestroy(msg);

What would it going to do? Where to put this?

Well..Trying this will not do anything as it is already commented.