Why is my Qt application crashing when accessing the IWMPMedia interface? - c++

Question

I have built a Qt (5.7) application that interfaces with the Windows Media Player COM API to parse track meta data. For some in-explicit reason my application is crashing when calling into IWMPMedia3::getAttributeCountByType.
The line where the crash keeps occurring is:
if (pMedia3Item && pMedia3Item->getAttributeCountByType(L"TrackingID", 0, &l) == S_OK) //Will eventually crash here
It does not crash on the first instance, it takes a couple of hundred loops and seems to be connected to when the call repeatedly returns 0. If I switch to an attribute that I know exists then it runs fine.
What is posted below is the object stripped right back, but it still crashes. This object is designed to run in its own QThread and all the COM symbols are defined and contained within the QThread.
The code forms part of a larger app that makes use of many other Qt modules, GUI, web engine being two of the biggest.
#include "WMPMLImport.h"
#include <QDebug>
#include "Wininet.h"
#define WMP_CLSID L"{6BF52A52-394A-11d3-B153-00C04F79FAA6}"
#define WMP_REFIID L"{D84CCA99-CCE2-11d2-9ECC-0000F8085981}"
#define WMP_PL_ALL_MUSIC L"All Music"
#define SAFE_RELEASE(ptr) if(NULL!=(ptr)){(ptr)->Release();ptr=NULL;}
#define BSTR_RELEASE(bstr) {SysFreeString(bstr);(bstr)=NULL;}
class CCoInitialize
{
public:
CCoInitialize() :
m_hr(CoInitialize(NULL))
{}
~CCoInitialize()
{
if(SUCCEEDED(m_hr)) {
qDebug() << "CCoInitialize: DTOR";
CoUninitialize();
}
}
HRESULT m_hr;
};
/**
Worker class that will step through the WMP COM interface
and extact the audio meta data contained within it,
*/
class WMPMLComHandler : public QObject
{
public:
WMPMLComHandler(WMPMLImport* t) :
m_thread(t)
{
qDebug() << "WMPMLComHandler::CTOR" << QThread::currentThreadId();
}
~WMPMLComHandler()
{
qDebug() << "WMPMLComHandler::DTOR" << QThread::currentThreadId();
}
/**
Method responsible for walking through the COM interface and extracting
all the track and playlist metadata including the artwork.
#returns Return false if the COM API was not parsed correctly.
*/
bool parse()
{
bool b = true;
CCoInitialize cCoInit;
IWMPCore* pIWMPCore = NULL;
IWMPCore3* pIWMPCore3 = NULL;
IWMPPlaylistCollection *pPlaylistCollection;
IWMPPlaylist *pMainLibplaylist;
CLSID clsID;
CLSID refID;
CLSIDFromString(WMP_CLSID, &clsID);
CLSIDFromString(WMP_REFIID, &refID);
if(SUCCEEDED(CoCreateInstance(clsID, NULL, CLSCTX_ALL, refID, (void**)&pIWMPCore)))
{
if(SUCCEEDED(pIWMPCore->get_playlistCollection(&pPlaylistCollection)))
{
if(SUCCEEDED(pIWMPCore->QueryInterface(__uuidof(IWMPCore3), reinterpret_cast<void**>(&pIWMPCore3))))
{
IWMPPlaylistArray* pPlaylistArray = NULL;
if(SUCCEEDED(pPlaylistCollection->getAll(&pPlaylistArray)))
{
long playlistCount = 0;
if(SUCCEEDED(pPlaylistArray->get_count(&playlistCount)))
{
IWMPPlaylist* pPlaylist = NULL;
for(int playlistIndex=0; playlistIndex < playlistCount; playlistIndex++)
{
if (SUCCEEDED(pPlaylistArray->item(playlistIndex, &pPlaylist)))
{
long lMediaCount = 0;
if (SUCCEEDED(pPlaylist->get_count(&lMediaCount)))
{
fetchPlaylist(pPlaylist, NULL, playlistIndex, lMediaCount);
}
SAFE_RELEASE(pPlaylist);
}
}
}
SAFE_RELEASE(pPlaylistArray);
}
SAFE_RELEASE(pIWMPCore3);
}
SAFE_RELEASE(pPlaylistCollection);
}
SAFE_RELEASE(pIWMPCore);
}
SAFE_RELEASE(pMainLibplaylist);
return b;
}
private:
void fetchPlaylist(IWMPPlaylist* pPlaylist, BSTR bstrName, unsigned int playlistIndex, long count)
{
//get the playlist items
for(long mediaIndex=0; mediaIndex<count-1; mediaIndex++)
{
IWMPMedia* pMediaItem = NULL;
if(SUCCEEDED(pPlaylist->get_item(mediaIndex, &pMediaItem)))
{
IWMPMedia3 *pMedia3Item = NULL;
if (pMediaItem->QueryInterface(__uuidof(IWMPMedia3), reinterpret_cast<void **>(&pMedia3Item)) == S_OK)
{
long l = 0;
qDebug() << "About to call method for" << mediaIndex << "time";
if (pMedia3Item && pMedia3Item->getAttributeCountByType(L"TrackingID", 0, &l) == S_OK) //Will eventually crash here
{
qDebug() << "Exited method for" << mediaIndex << "time";
}
}
SAFE_RELEASE(pMedia3Item);
SAFE_RELEASE(pMediaItem);
}
}
qDebug() << "*********COMPLETE*********";
}
WMPMLImport* m_thread;
};
//==
WMPMLImport::WMPMLImport() :
m_comHandler(NULL)
{
qDebug() << "WMPMLImporter CTOR" << QThread::currentThreadId();
}
WMPMLImport::~WMPMLImport()
{
}
/**
Reimplemented function that runs the function contents in a new thread context.
The parsing of the COM is all ran through this thread. Returning out of this
thread will end its execution.
*/
void WMPMLImport::run()
{
QMutexLocker g(&m_lock);
m_comHandler = new WMPMLComHandler(this);
g.unlock();
bool parseOk = m_comHandler->parse();
g.relock();
delete m_comHandler;
m_comHandler = NULL;
}