Strange problem with QThread

**akaWolf** · 30th May 2013, 11:51

Hello!

I'm writing a small program in Qt 5.0 under Windows 7 with msvc2010 toolchain. But in the process of writing I met a rather problem: Exception. Access violation - code c0000005.
Created a test project that enclose below.
The problem as follows:
I'm creating a "thread", in which a "test" is being perfomed. "Test" creates another "thread", which runs in an endless cycle of reading. In the test I create CCANReceiver, which begins to read data from the device, and then send the data. I wait for 5 seconds and close the thread with CCANReceiver. But when trying to call StopReceiving () function while calling IsRunning () I get the exception. Empirically I found that if a function ReadDMADataOneBlock
ReadDMADataOneBlock () - function of libraries provided by me to work with the device. The source codes are available.
Source code in attachment. I do not include the library, because without the device driver and it will not work, but I can put the source code.

Detailed error information:

(d08.d68): Access violation - code c0000005 (first chance)
s
sException at 0x6704c87c, code: 0xc0000005: write access violation at: 0x1, flags=0x0 (first chance) at q:\qt5_workdir\w\s\qtbase\src\corelib\arch\qatomic _msvc.h:351
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
eax=00000000 ebx=00000000 ecx=00000001 edx=00000040 esi=00000007 edi=01d6dfc4
eip=6704c87c esp=01d6d444 ebp=01d6d444 iopl=0 nv up ei pl nz na pe nc
cs=001b ss=0023 ds=0023 es=0023 fs=003b gs=0000 efl=00010206
Qt5Cored!QAtomicOps<QMutexData *>::testAndSetRelaxed+0xc:
3516704c87c f00fb10a lock cmpxchg dword ptr [edx],ecx ds:0023:00000040=????????

Call stack at the moment of program down:

0 QAtomicOps<QMutexData *>::testAndSetRelaxed qatomic_msvc.h 351 0x6704c87c
1 QGenericAtomicOps<QAtomicOps<QMutexData *> >::testAndSetAcquire<QMutexData *,QMutexData *> qgenericatomic.h 150 0x6704a8a5
2 QBasicAtomicPointer<QMutexData>::testAndSetAcquire qbasicatomic.h 229 0x67048e08
3 QBasicMutex::fastTryLock qmutex.h 87 0x670486f7
4 QMutex::lock qmutex.cpp 212 0x67069e11
5 QMutexLocker::QMutexLocker qmutex.h 133 0x670487e8
6 QThread::isRunning qthread.cpp 448 0x67070243
7 CCANReceiver::StopReceiving ccanreceiver.cpp 45 0x41c5e3

I do not understand how this could happen.
Debugging, I found out that this is most likely due to the fact that QScopedPointer >::data returns a value of 0.
Call stack:

0 QScopedPointer<QObjectData,QScopedPointerDeleter<Q ObjectData> >::data qscopedpointer.h 135 0x67041d4c
1 qGetPtrHelper<QScopedPointer<QObjectData,QScopedPo interDeleter<QObjectData> > > qglobal.h 991 0x670581ab
2 QThread::d_func qthread.h 136 0x670573d3
3 QThread::isRunning qthread.cpp 446 0x67070231
4 CCANReceiver::StopReceiving ccanreceiver.cpp 44 0x420423
5 CTest0::OnTimerTimeOut ctest0.cpp 324 0x41580e

Some source code:
ctest0.h

Qt Code:

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#ifndef CTEST0_H
#define CTEST0_H
 
#include "itest.h"
#include "CANDeviceEx.h"
#include "ccanreceiver.h"
#include <QTimer>
 
class CTest0 : public ITest
{
    Q_OBJECT
public:
    CTest0(ILogger* _Logger);
    virtual void SetFeature(quint64 NumFeat, quint64 ValFeat);
public slots:
    virtual void Run();
    void OnTimerTimeOut();
public:
    virtual QString GetName() const;
    virtual ~CTest0();
 
private:
    CCANDeviceEx CANDevice;
    CCANReceiver *CANReceiver;
 
    quint32 sendbuff[3];
    QTimer* Timer;
 
    quint32 mode1, mode2, sendchannel, bufnum;
    quint8 brp1, sjw1, sam1, btlmode1, phseg11, phseg21, prseg1, wakfil1;
    quint8 brp2, sjw2, sam2, btlmode2, phseg12, phseg22, prseg2, wakfil2;
};
 
#endif // CTEST0_H

#ifndef CTEST0_H
#define CTEST0_H

#include "itest.h"
#include "CANDeviceEx.h"
#include "ccanreceiver.h"
#include <QTimer>

class CTest0 : public ITest
{
    Q_OBJECT
public:
    CTest0(ILogger* _Logger);
    virtual void SetFeature(quint64 NumFeat, quint64 ValFeat);
public slots:
    virtual void Run();
    void OnTimerTimeOut();
public:
    virtual QString GetName() const;
    virtual ~CTest0();

private:
    CCANDeviceEx CANDevice;
    CCANReceiver *CANReceiver;

    quint32 sendbuff[3];
    QTimer* Timer;

    quint32 mode1, mode2, sendchannel, bufnum;
    quint8 brp1, sjw1, sam1, btlmode1, phseg11, phseg21, prseg1, wakfil1;
    quint8 brp2, sjw2, sam2, btlmode2, phseg12, phseg22, prseg2, wakfil2;
};

#endif // CTEST0_H

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ctest0.cpp

Qt Code:

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#include "ctest0.h"
 
CTest0::CTest0(ILogger* _Logger) :
    ITest(_Logger),
    CANReceiver(NULL),
    Timer(NULL)
{
}
 
void CTest0::Run()
{
    quint32 tmp = 0;
    quint32 tmpmode = 0;
    sendbuff[0] = 0x01020304;
    sendbuff[1] = 0x05060708;
    sendbuff[2] = 0x090A0B0C;
 
    if (CANReceiver != NULL)
    {
        delete CANReceiver;
        CANReceiver = NULL;
    }
 
    if (Timer != NULL)
    {
        delete Timer;
        Timer = NULL;
    }
 
    if (CANDevice.IsOpen())
        CANDevice.Close();
 
    Timer = new QTimer;
 
    QObject::connect(Timer, SIGNAL(timeout()), /*qobject_cast<CTest0*>*/(this), SLOT(OnTimerTimeOut()));
    QObject::connect(Timer, SIGNAL(qr()), this, SLOT(OnTimerTimeOut()));
    Timer->setInterval(5000);
    Timer->setSingleShot(true);
 
    /* ... */
 
    Logger->AddToLog("Trying to receive data");
 
    CANReceiver = new CCANReceiver(&CANDevice);
    CANReceiver->StartReceiving();
 
    Logger->AddToLog("Start 5s wait");
 
    Timer->start();
 
    Logger->AddToLog("Trying to send data over " + QString::number(sendchannel) + QString::number(bufnum));
 
    if ((tmp = CANDevice.SendData(sendchannel, bufnum, 0, sendbuff, 12)) != 1)
    {
        SetError("Can't send data, error = " + QString::number(tmp));
        Timer->stop();
        emit TestEnd();
        return;
    }
 
    Logger->AddToLog("Send " + QString::number(sizeof(sendbuff)) + " bytes");
}
 
void CTest0::SetFeature(quint64 NumFeat, quint64 ValFeat)
{
    switch (NumFeat)
    {
    case 0:
        mode1 = ValFeat;
        break;
 
    case 1:
        mode2 = ValFeat;
        break;
 
    /* ... */
 
    case 19:
        bufnum = ValFeat;
        break;
 
    default:
        break;
    }
}
 
CTest0::~CTest0()
{
    if (CANDevice.IsOpen())
        CANDevice.Close();
 
    if (CANReceiver != NULL)
        delete CANReceiver;
 
    if (Timer != NULL)
        delete Timer;
}
 
QString CTest0::GetName() const
{
    return "Test 0";
}
 
void CTest0::OnTimerTimeOut()
{
    Logger->AddToLog("Stop 5s wait");
 
    CANReceiver->StopReceiving();
 
    if (!CANReceiver->GetLastError().isEmpty())
    {
        SetError("Can't receive data, error \"" + CANReceiver->GetLastError() + "\"");
        emit TestEnd();
        return;
    }
 
    Logger->AddToLog("Succesfully receive " + QString::number(CANReceiver->GetBufferSize()) + " bytes");
 
}

#include "ctest0.h"

CTest0::CTest0(ILogger* _Logger) :
    ITest(_Logger),
    CANReceiver(NULL),
    Timer(NULL)
{
}

void CTest0::Run()
{
    quint32 tmp = 0;
    quint32 tmpmode = 0;
    sendbuff[0] = 0x01020304;
    sendbuff[1] = 0x05060708;
    sendbuff[2] = 0x090A0B0C;
    
    if (CANReceiver != NULL)
    {
        delete CANReceiver;
        CANReceiver = NULL;
    }

    if (Timer != NULL)
    {
        delete Timer;
        Timer = NULL;
    }

    if (CANDevice.IsOpen())
        CANDevice.Close();

    Timer = new QTimer;

    QObject::connect(Timer, SIGNAL(timeout()), /*qobject_cast<CTest0*>*/(this), SLOT(OnTimerTimeOut()));
    QObject::connect(Timer, SIGNAL(qr()), this, SLOT(OnTimerTimeOut()));
    Timer->setInterval(5000);
    Timer->setSingleShot(true);
    
    /* ... */

    Logger->AddToLog("Trying to receive data");

    CANReceiver = new CCANReceiver(&CANDevice);
    CANReceiver->StartReceiving();

    Logger->AddToLog("Start 5s wait");

    Timer->start();

    Logger->AddToLog("Trying to send data over " + QString::number(sendchannel) + QString::number(bufnum));

    if ((tmp = CANDevice.SendData(sendchannel, bufnum, 0, sendbuff, 12)) != 1)
    {
        SetError("Can't send data, error = " + QString::number(tmp));
        Timer->stop();
        emit TestEnd();
        return;
    }

    Logger->AddToLog("Send " + QString::number(sizeof(sendbuff)) + " bytes");
}

void CTest0::SetFeature(quint64 NumFeat, quint64 ValFeat)
{
    switch (NumFeat)
    {
    case 0:
        mode1 = ValFeat;
        break;

    case 1:
        mode2 = ValFeat;
        break;

    /* ... */

    case 19:
        bufnum = ValFeat;
        break;

    default:
        break;
    }
}

CTest0::~CTest0()
{
    if (CANDevice.IsOpen())
        CANDevice.Close();

    if (CANReceiver != NULL)
        delete CANReceiver;

    if (Timer != NULL)
        delete Timer;
}

QString CTest0::GetName() const
{
    return "Test 0";
}

void CTest0::OnTimerTimeOut()
{
    Logger->AddToLog("Stop 5s wait");

    CANReceiver->StopReceiving();

    if (!CANReceiver->GetLastError().isEmpty())
    {
        SetError("Can't receive data, error \"" + CANReceiver->GetLastError() + "\"");
        emit TestEnd();
        return;
    }

    Logger->AddToLog("Succesfully receive " + QString::number(CANReceiver->GetBufferSize()) + " bytes");

}

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ccanreceiver.h

Qt Code:

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#ifndef CCANRECEIVER_H
#define CCANRECEIVER_H
 
#include <QList>
#include "clasterror.h"
#include "CANDeviceEx.h"
#include <QThread>
#include "CANHeader.h"
 
class CCANReceiver;
 
class CCANReceiverHelper : public QObject, public CLastError
{
    Q_OBJECT
public:
    CCANReceiverHelper(CCANReceiver* _CANReceiver, CCANDeviceEx* _CANDevice);
    ~CCANReceiverHelper();
    void StopWork();
 
public slots:
    void DoWork();
 
private:
    CCANReceiver* CANReceiver;
    CCANDeviceEx* CANDevice;
    bool Stopped;
    _MSG_INPUT rcvblock;
};
 
class CCANReceiver : public CLastError
{
public:
    CCANReceiver(CCANDeviceEx* _CANDevice);
    ~CCANReceiver();
 
    void ClearBuffer();
    QList<quint8> GetBuffer() const;
    quint64 GetBufferSize() const;
    void StartReceiving();
    void StopReceiving();
    friend class CCANReceiverHelper;
 
private:
    void AddToBuffer(quint8 data);
 
private:
    QList<quint8> buffer;
    CCANReceiverHelper CANReceiverHelper;
    QThread CANReceiverHelperThread;
};

#ifndef CCANRECEIVER_H
#define CCANRECEIVER_H

#include <QList>
#include "clasterror.h"
#include "CANDeviceEx.h"
#include <QThread>
#include "CANHeader.h"

class CCANReceiver;

class CCANReceiverHelper : public QObject, public CLastError
{
    Q_OBJECT
public:
    CCANReceiverHelper(CCANReceiver* _CANReceiver, CCANDeviceEx* _CANDevice);
    ~CCANReceiverHelper();
    void StopWork();

public slots:
    void DoWork();

private:
    CCANReceiver* CANReceiver;
    CCANDeviceEx* CANDevice;
    bool Stopped;
    _MSG_INPUT rcvblock;
};

class CCANReceiver : public CLastError
{
public:
    CCANReceiver(CCANDeviceEx* _CANDevice);
    ~CCANReceiver();

    void ClearBuffer();
    QList<quint8> GetBuffer() const;
    quint64 GetBufferSize() const;
    void StartReceiving();
    void StopReceiving();
    friend class CCANReceiverHelper;

private:
    void AddToBuffer(quint8 data);

private:
    QList<quint8> buffer;
    CCANReceiverHelper CANReceiverHelper;
    QThread CANReceiverHelperThread;
};

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ccanreceiver.cpp

Qt Code:

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#include "ccanreceiver.h"
 
CCANReceiver::CCANReceiver(CCANDeviceEx *_CANDevice) :
    CANReceiverHelper(this, _CANDevice)
{
    buffer.clear();
    CANReceiverHelper.moveToThread(&CANReceiverHelperThread);
    QObject::connect(&CANReceiverHelperThread, SIGNAL(started()), &CANReceiverHelper, SLOT(DoWork()));
}
 
CCANReceiver::~CCANReceiver()
{
 
}
 
void CCANReceiver::ClearBuffer()
{
    buffer.clear();
}
 
QList<quint8> CCANReceiver::GetBuffer() const
{
    return buffer;
}
 
quint64 CCANReceiver::GetBufferSize() const
{
    return buffer.size();
}
 
void CCANReceiver::AddToBuffer(quint8 data)
{
    buffer.append(data);
}
 
void CCANReceiver::StartReceiving()
{
    if (!CANReceiverHelperThread.isRunning())
        CANReceiverHelperThread.start();
}
 
void CCANReceiver::StopReceiving()
{
    if (CANReceiverHelperThread.isRunning())
    {
        CANReceiverHelper.StopWork();
        CANReceiverHelperThread.quit();
        CANReceiverHelperThread.wait();
    }
}
 
CCANReceiverHelper::CCANReceiverHelper(CCANReceiver *_CANReceiver, CCANDeviceEx *_CANDevice) :
    CANReceiver(_CANReceiver),
    CANDevice(_CANDevice),
    Stopped(false)
{
 
}
 
void CCANReceiverHelper::StopWork()
{
    Stopped = true;
}
 
CCANReceiverHelper::~CCANReceiverHelper()
{
 
}
 
quint64 fact(quint64 n)
{
    if (n <= 1)
        return 1;
    else
        return fact(n - 1) * n;
}
 
void CCANReceiverHelper::DoWork()
{
    while (1)
    {
        quint32 res = 0;
        quint32 tmp = 0;
 
        do
        {
            if (Stopped)
                return;
 
            if ((tmp = CANDevice->GetDMAReadyStatus(&res)) != 1)
            {
                CANReceiver->SetError("Can't get DMA ready status, error = " + QString::number(tmp));
                return;
            }
        }
        while (!res);
        if ((tmp = CANDevice->ReadDMADataOneBlock((void*)&rcvblock)) != 1)
        {
            CANReceiver->SetError("Can't read DMA one block, error = " + QString::number(tmp));
            return;
        }
        for (quint8 i = 0; i < rcvblock.RXB0DLC.DLC; i++)
        {
            CANReceiver->AddToBuffer(rcvblock.data.all[i]);
        }
    }
}
#endif // CCANRECEIVER_H

#include "ccanreceiver.h"

CCANReceiver::CCANReceiver(CCANDeviceEx *_CANDevice) :
    CANReceiverHelper(this, _CANDevice)
{
    buffer.clear();
    CANReceiverHelper.moveToThread(&CANReceiverHelperThread);
    QObject::connect(&CANReceiverHelperThread, SIGNAL(started()), &CANReceiverHelper, SLOT(DoWork()));
}

CCANReceiver::~CCANReceiver()
{

}

void CCANReceiver::ClearBuffer()
{
    buffer.clear();
}

QList<quint8> CCANReceiver::GetBuffer() const
{
    return buffer;
}

quint64 CCANReceiver::GetBufferSize() const
{
    return buffer.size();
}

void CCANReceiver::AddToBuffer(quint8 data)
{
    buffer.append(data);
}

void CCANReceiver::StartReceiving()
{
    if (!CANReceiverHelperThread.isRunning())
        CANReceiverHelperThread.start();
}

void CCANReceiver::StopReceiving()
{
    if (CANReceiverHelperThread.isRunning())
    {
        CANReceiverHelper.StopWork();
        CANReceiverHelperThread.quit();
        CANReceiverHelperThread.wait();
    }
}

CCANReceiverHelper::CCANReceiverHelper(CCANReceiver *_CANReceiver, CCANDeviceEx *_CANDevice) :
    CANReceiver(_CANReceiver),
    CANDevice(_CANDevice),
    Stopped(false)
{

}

void CCANReceiverHelper::StopWork()
{
    Stopped = true;
}

CCANReceiverHelper::~CCANReceiverHelper()
{

}

quint64 fact(quint64 n)
{
    if (n <= 1)
        return 1;
    else
        return fact(n - 1) * n;
}

void CCANReceiverHelper::DoWork()
{
    while (1)
    {
        quint32 res = 0;
        quint32 tmp = 0;

        do
        {
            if (Stopped)
                return;

            if ((tmp = CANDevice->GetDMAReadyStatus(&res)) != 1)
            {
                CANReceiver->SetError("Can't get DMA ready status, error = " + QString::number(tmp));
                return;
            }
        }
        while (!res);
        if ((tmp = CANDevice->ReadDMADataOneBlock((void*)&rcvblock)) != 1)
        {
            CANReceiver->SetError("Can't read DMA one block, error = " + QString::number(tmp));
            return;
        }
        for (quint8 i = 0; i < rcvblock.RXB0DLC.DLC; i++)
        {
            CANReceiver->AddToBuffer(rcvblock.data.all[i]);
        }
    }
}
#endif // CCANRECEIVER_H

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I beg for your help.
Sincerely, akaWolf.

Added after 8 minutes:

I described this problem before, but no one could help me.

**anda_skoa** · 30th May 2013, 12:59

The code looks very fragile, it access data from different threads without any protection.

To further simplify the problem I would recommend getting rid of the outer thread.

Cheers,
_

**akaWolf** · 30th May 2013, 14:10

Thank you, I've already solved this problem: it was problem with my colleauge's library because it wrote where it shouldn't. This bug happened to be very covert and i could recognize it long time ago after wrong piece of code was executed..

**anda_skoa** · 31st May 2013, 14:25

Ah, good

Btw, you don't need to check a pointer before calling delete on it, delete 0 is perfectly fine for C++.

Cheers,
_

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