QThread crashes the program?

Question

I implement QThread like this, but get program crashed when it runs.
I've searched and seen posts saying it is not the correct way to use QThread.
But I cannot find any reason for the crashes of my program, what I do is only triggering 'on_Create_triggered()' and I guarantee the mutex is locked and unlocked properly.
I have tested the program for two days(testing only by 'std::cerr << ...;' prints results), but still cannot find reason. What I guess is that the thread may wait for the lock too long and cause program to crash. (not sounds reasonable...) :)

My codes:

Background.h

class Background : public QThread
{
    Q_OBJECT

public:
    Background(int& val,DEVMAP& map, QQueue<LogInfoItem*>& queue, QList<DEV*>& devlist, QList<IconLabel*>& icllist,QMutex& m)
        :val_i(val),DevMap(map), LogInfoQueue(queue), DevInfoList(devlist), IconLabelList(icllist),mutex(m)
    {}

     ~Background();

protected:
    void run(void);


private:
    DEVMAP& DevMap;
    QQueue<LogInfoItem*>&LogInfoQueue;
    QList<DEV*>& DevInfoList;
    QList<IconLabel*>& IconLabelList;
    int& val_i;
    QMutex& mutex;



    void rcv();



};

Background.cpp

#include "background.h"


Background::~Background()
{
    LogFile->close();
}

void Background::run(void)
{
    initFile();

    while(1)
    {
        msleep(5);
        rcv();
    }

}


void Background::rcv()
{
    mutex.lock();
    ...
    ...//access DevMap, LogInfoQueue, DevInfoList, IconLabelList and val_i;
    ...
    mutex.unlock();
}

MainWindow:(MainWindow has Background* back as property)

void MainWindow::initThread()
{
    back = new Background(val_i, dev_map, logDisplayQueue, devInfoList, iconLabelList, mutex);
    back->start();
}

void MainWindow::on_Create_triggered()
{
    mutex.lock();
    ...
    ...//access DevMap, LogInfoQueue, DevInfoList, IconLabelList and val_i;
    ...
    mutex.unlock();
}

Any where, almost. Not the same place. Often When the thread waits the lock.(I found it from the stream printed out not by debugger...:) — Al2O3, Oct 19 '12 at 15:02
Now I really suspect a QTimer in my program(in MainWindow). Even when I donnot connect it to any SLOT but 'timer = new QTimer()' and 'timer->start(1000)' will crash the program, but everything seems to work well with the two setences commentted... :) — Al2O3, Oct 19 '12 at 15:11
You're not providing enough information (code) for anyone to be able to help you. You also seem to be implying that QThread and/or QTimer are causing your crashes. Google "Select isn't broken". It's very highly unlikely that either of those classes are the cause of your crashes. It's much more likely a problem in your code. — kenrogers, Oct 19 '12 at 17:30
Yeah, Thank you!!! Tahnks for your hints!! I just do not have enough confidence for what I use, like QThread or Qtimer, and worry some unexpected unsafe links between them, I even want to change to use Pthread or std::thread because of bad comments about QThread. But now I totally trust what qt library supplies, and I have found the reason...(see my answer:)) — Al2O3, Oct 20 '12 at 01:43

score 0 · Accepted Answer · answered Oct 20 '12 at 02:40

I have found the reason, which is more subtle.
(I use some codes written by others but believe it is not broken, what I got totally wrong! :) )
The broken codes:

#define   DATABUFLEN    96

typedef struct Para//totally  100bytes
{
    UINT8 type;
    UINT8 len;
    UINT8 inType;
    UINT8 inLen;
    UINT8 value[DATABUFLEN];//96 bytes here
}ERRORTLV;


class BitState
{

public:
    UINT8                           dataBuf[DATABUFLEN];
    ......

};

And the function using it:

bool    BitState::rcvData()               //the function crosses bound of array
{

    UINT8 data[12] = 
        {
            0x72, 0x0A, 0x97, 0x08,
            0x06, 0x0A, 0x0C, 0x0F,
            0x1E, 0x2A, 0x50, 0x5F,
        };                                //only 12 bytes

    UINT32 dataLen = 110;

    memcpy(this->dataBuf, data, dataLen); //copy 110 bytes to dataBuf //but no error or warning from compiler, and no runtime error indicates the cross
}


bool    BitState::parseData(BitLog* bitLog)//pass pointer of dataBuf to para_tmp, but only use  0x08 + 4 = 12 bytes of dataBuf
{


    Para* para_tmp;
    if(*(this->dataBuf) == 0x77)
    {
        para_tmp = (ERRORTLV*)this->dataBuf;
    }

    if(para_tmp->type != 0x72 || para_tmp->inType != 0x97 || (para_tmp->len - para_tmp->inLen) != 2)                                                        // inLen == 0x08
    {
        return false;
    }
    else
    {
        //parse dataBuf according to Para's structure


        this->bitState.reset();


        for(int i = 0; i < para_tmp->inLen; i++)          // inLen == 0x08 only !!!
        {
            this->bitState[para_tmp->value[i]-6] = 1;
        }


        if(this->bitState.none())
            this->setState(NORMAL);
        else
            this->setState(FAULT);

         QString currentTime = (QDateTime::currentDateTime()).toString("yyyy.MM.dd hh:mm:ss.zzz");

         string sysTime = string((const char *)currentTime.toLocal8Bit());

         this->setCurTime(sysTime);

        this->addLog(sysTime, bitLog);

    }

    return true;
}



bool    BitState::addLog(std::string sysTime, BitLog* bitLog)// this function is right
{

        bitLog->basicInfo = this->basicInfo;//not in data Buf, already allocated and initialized, (right)
        bitLog->bitState = this->bitState;  //state is set by setState(..)

        bitLog->rcvTime = sysTime;          //time 

        return true;
}

Generally speaking, the program allocates 96 bytes to a byte array, but use 'memcpy(...)' to copy 110 bytes to the array, later uses only 12 bytes of the array.
All kinds of crashes appear, which are confusing and frustrating...:( :( :(

QThread crashes the program?

1 Answers1