无法终止分叉过程

Question

I have a process which has to be terminated using Ctrl-C or SIGINT. In this case I cannot use Ctrl-C physically with the keyboard, so it has to done using a kill command in C. This code basically reads GPIO input and starts and stops a script record.sh , a GStreamer command line script.

I only want to terminate the child process created in startVideoRecording(). I need to do start, stop, start, stop the recording as many times as I like. It's not a one-off thing.

However, when I change the gpio value and trigger stopAllRecordings(), it doesn't send the SIGINT to the child process. It just hangs there at "Sending interrupt to GStreamer process.. Status 0"

How can I make sure that the video recording process is terminated with a Ctrl-C equivalent?

Thanks.

Here's the code :

int main() {
    pollGPIOSwitch(&vn200);
}


void* pollGPIOSwitch(void* arg) {


   Vn200* vn200 = (Vn200*)arg;
   int fd;
   char buf[100];
   char value; 
   int videoRecError;
   bool videoRecOn = false;

   sprintf(buf, "/sys/class/gpio/gpio56/value");

   while (KEEP_GOING) {
       fd = open(buf,O_RDONLY);
       lseek(fd,0,SEEK_SET); // move to beginning of file
       read(fd,&value,1);
       if (value=='0') {
           if (videoRecOn) { // recording on, switch off, end recording
               stopAllRecordings();
               videoRecOn = false;
               TriggerGPSINSThreadExit = 0; // reset variables
               printf("Reset GPSINS Thread variables.\n");
           }
       }
       else if (!videoRecOn) { // recording off, switch on, start recording
            if (pthread_create(&GPSINSLoggingThread, NULL, runGPSINS,(void*) vn200) != 0) {
                printf("Error: Fail to create runGPSINS thread\n");
            }

            videoRecError = startVideoRecording();
            if (videoRecError == -1)
                pthread_exit(&videoRecError);
            videoRecOn = true; 
       }
       usleep(500000);
   }
   close(fd);


   printf("Exited Polling!");
}

int startVideoRecording() {
    int error;
    error = 0;

    if ((AVRecordingProcess = fork()) != -1) {
        switch (AVRecordingProcess) {
            case -1:
                printf("Error: Fail to create AVRecordingProcess\n");
                error = -1;
            case 0:
                execl("record.sh", "0", NULL);
                //system("//root//record.sh");
                printf("Error: Fail to execute AVRecordingProcess\n");
                error = -1;
            default:
               printf("Video Recording...process id %d\n", AVRecordingProcess); 
                break;
        }
    } else {  
        printf("Error: MainHost failed to fork AVRecordingProcess\n");
        error = -1;
    } 

    return error;

}


void stopAllRecordings() {
    int ret; 
    FILE *infile, *outfile;
    int ch;


    printf("Terminating child processes..%d\n", AVRecordingProcess);
    ret = kill(AVRecordingProcess, SIGINT);
    printf("Sending interrupt to GStreamer process.. Status %d\n", ret);

    int status;
    printf("Wait for the GStreamer process %d to end....", AVRecordingProcess);
    wait(AVRecordingProcess);
    printf("GStreamer ended.\n"); 
}

Answer 1

Is it possible that you are starting multiple child processes and only sending SIGINT to the last child process you created and not earlier ones? Type 'PS' and hit enter after starting this program and see how many processes you have started.

Answer 2

I eventually did this :

int startVideoRecording() {
    int error;
    error = 0;

    if ((AVRecordingProcess = fork()) != -1) {
        switch (AVRecordingProcess) {
            case -1:
                printf("Error: Fail to create AVRecordingProcess\n");
                error = -1;
            case 0:
                setpgid(AVRecordingProcess,0);  <-- NEW
                execl("record.sh", "0", NULL);
                //system("//root//record.sh");
                printf("Error: Fail to execute AVRecordingProcess\n");
                error = -1;
            default:
               printf("Video Recording...process id %d\n", AVRecordingProcess); 
                break;
        }
    } else {  
        printf("Error: MainHost failed to fork AVRecordingProcess\n");
        error = -1;
    } 

    return error;

}

void stopAllRecordings() {
    int ret; 
    FILE *infile, *outfile;
    int ch;


    printf("Terminating child processes..%d\n", AVRecordingProcess);
    ret = killpg(AVRecordingProcess, SIGINT); <-- NEW
    printf("Sending interrupt to GStreamer process.. Status %d\n", ret);

    int status;
    printf("Wait for the GStreamer process %d to end....", AVRecordingProcess);
    waitpid(AVRecordingProcess,0,0); <-- NEW
    printf("GStreamer ended.\n"); 
}

and it works.

Basically, during the creation of the AVRecordingProcess, I set it as the head of the process group. Sending the process group SIGINT sends it also to the rest of the processes within the group. To make sure the process group ended, I used waitpid.

Linux experts, feel free to correct me, thanks!