Use hog.detectMultiScale in multiple threads?

edit

When I do pedestrian detection width Hog + SVM in OpenCV ,I try to using it in two thread to improve the detect speed.But I got OpenCV error: Assertion failed<s >=0> in unknown function,file ..\..\..\opencv\modules\core\src\matrix.cpp,line 116

My code:

DWORD WINAPI DetectFrame1(LPVOID lpPrarmeter){
    HOGDescriptor hog1;
    hog1.setSVMDetector(HOGDescriptor::getDefaultPeopleDetector());

    while(true){
        WaitForSingleObject(g_hEvent1,INFINITE);        

        int temp;
        hog1.detectMultiScale(detImg1, found1, 0, cv::Size(8,8), cv::Size(0,0), 1.08, 2);  
        //cout<<"得到一帧near :"<<frame<<endl;
        //temp=frame;       // 标志当前处理帧 [9/26/2014 pan]

        if(!detImg1.empty()){
            imshow("det1",detImg1);
        }
        waitKey(10);
        cout<<"1——检测到行人："<<found1.size()<<endl;
        SetEvent(g_hEvent1);
    }
    return 0;
}
DWORD WINAPI DetectFrame2(LPVOID lpPrarmeter){
    HOGDescriptor hog2;
    hog2.setSVMDetector(HOGDescriptor::getDefaultPeopleDetector());         // 该函数不能并发 [9/26/2014 pan]
    while(true){    
        WaitForSingleObject(g_hEvent2,INFINITE);    
        int temp;
        //cout<<"得到一帧far :"<<frame<<endl;
        //temp=frame;           // 标志当前处理帧 [9/26/2014 pan]
        hog2.detectMultiScale(detImg2, found2, 0, cv::Size(8,8), cv::Size(0,0), 1.08, 2);  

        if(!detImg2.empty()){
            imshow("det2",detImg2);
        }
        waitKey(10);
        cout<<"2——检测到行人："<<found2.size()<<endl;
        SetEvent(g_hEvent2);        // 变为有信号状态 [9/26/2014 pan]
    }
    return 0;
}

Can anyone help me ,thanks.