Opencv Segmentation Fault 使用 pthread 捕获帧 C++

Question

我在尝试运行我的程序时收到分段错误。在修改我的程序以从不同线程上的两个摄像头捕获帧后，我只收到分段错误。我在两个线程上都使用了相同的函数，我想知道这是否是问题所在。

Main.c

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <time.h>
#include <opencv2/opencv.hpp>
#include "ThreadedWebcamCapture.h"

pthread_mutex_t mutex1 = PTHREAD_MUTEX_INITIALIZER;

int main(){
    ThreadedCapture Capture1;
    Capture1.STOP = 0;
    Capture1.CAP_NUMBER = 1;
    Capture1.X_RESOLUTION = 640;
    Capture1.Y_RESOLUTION = 480;

    ThreadedCapture Capture2;
    Capture2.STOP = 0;
    Capture2.CAP_NUMBER = 0;
    Capture2.X_RESOLUTION = 640;
    Capture2.Y_RESOLUTION = 480;

    pthread_t Capture1Thread;
    int Capture1ThreadRetCode;

    pthread_t Capture2Thread;
    int Capture2ThreadRetCode;

    printf("[INFO]Creating Threads\n");
    Capture1ThreadRetCode = pthread_create(&Capture1Thread, NULL, &Capture_Thread, (void *)&Capture1);
    printf("[INFO]Created Thread 1");
    Capture2ThreadRetCode = pthread_create(&Capture2Thread, NULL, &Capture_Thread, (void *)&Capture2); //I think the error is occurring here
    if(Capture1ThreadRetCode || Capture2ThreadRetCode != 0){
        printf("[ERROR]Thread Creation Failed!\n");
        exit(EXIT_FAILURE);
    }
    //cv::namedWindow("Window", cv::WINDOW_AUTOSIZE);
    int NumberOfFrames;
    time_t Seconds1;
    Seconds1 = time(NULL);
    cv::Mat Output;
    while(1 == 1){
        pthread_mutex_lock(&mutex1);
        if(!Capture1.FRAME.empty() || !Capture2.FRAME.empty()){
            cv::hconcat(Capture1.FRAME, Capture2.FRAME, Output);
        }
        pthread_mutex_unlock(&mutex1);
        if(!Output.empty()){
            NumberOfFrames = NumberOfFrames + 1;
            cv::imshow("Window", Output);
        }
        if(cv::waitKeyEx(1) >= 0){
            Capture1.STOP = 1;
            Capture2.STOP = 1;
            break;
        }
    }
    time_t Seconds2;
    Seconds2 = time(NULL);
    int Seconds = Seconds2 - Seconds1;
    int FPS = NumberOfFrames / Seconds;
    printf("[INFO]FPS %d\n", FPS);
    pthread_join(Capture1Thread, NULL);
    pthread_join(Capture2Thread, NULL);
    printf("[INFO]Done\n");
    return(0);
}

cvthreads.c

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <opencv2/opencv.hpp>
#include "ThreadedWebcamCapture.h"

void *Capture_Thread(void* Test){
    ThreadedCapture *Testing = (ThreadedCapture *) Test;
    cv::VideoCapture CAP ((*Testing).CAP_NUMBER);
    CAP.set(CV_CAP_PROP_FRAME_WIDTH, (*Testing).X_RESOLUTION);
    CAP.set(CV_CAP_PROP_FRAME_HEIGHT, (*Testing).Y_RESOLUTION);
    while((*Testing).STOP != 1){
        CAP.read((*Testing).FRAME);
    }
    return(NULL);
}

ThreadedWebcamCapture.h

#ifndef _THREADEDWEBCAMCAPTURE_H_
#define _THREADEDWEBCAMCAPTURE_H_

void *Capture_Thread(void* Test);

typedef struct ThreadedCaptures  {
    int STOP;
    int CAP_NUMBER;
    int X_RESOLUTION;
    int Y_RESOLUTION;
    cv::Mat FRAME;
} ThreadedCapture;

#endif

Answer 1

您的问题在于 cv::hconcat 函数，特别是传递两个具有不同行数的 cv::Mat 对象。如果您查看cv::hconcat 函数的documentation，它表示给定的两个矩阵必须具有相同的行数。您还可以看到，在 strace 结果的最后几行中，有一个断言错误，指出发送到cv::hconcat 的行数不相等。

"OpenCV Error: Assertion failed ("..., 205OpenCV Error: Assertion failed (src[i].dims <= 2 && src[i].rows == src[0].rows && src[i].type() == src[0].type()) in hconcat, file /builddir/build/BUILD/opencv-3.2.0/modules/core/src/matrix.cpp, line 2865

现在，此错误的原因在于以下几行：

if(!Capture1.FRAME.empty() || !Capture2.FRAME.empty()){
    cv::hconcat(Capture1.FRAME, Capture2.FRAME, Output);
}

如果任何矩阵不为空，则执行水平串联操作。但是，这意味着其中一个矩阵的大小可能为 640x480，而另一个矩阵的大小可能为 0x0。在这种情况下，cv::hconcat 会抛出一个断言错误并且你的程序会崩溃。要修复它，请尝试将条件更改为

if(!Capture1.FRAME.empty() && !Capture2.FRAME.empty()){
    cv::hconcat(Capture1.FRAME, Capture2.FRAME, Output);
}

只有当两个矩阵都不为空时才执行操作。它们应该具有相同的行数，因为您构建的 ThreadedCapture 对象具有相同的行数。

参考文献

• https://docs.opencv.org/master/d2/de8/group__core__array.html#gaf9771c991763233866bf76b5b5d1776f