C中两个进程之间的同步

Question

I am trying to send signals between two child in alternative way for 100 times.

Here is my snippet of code.

here is the link to the whole question: sending signal between two child process

But i have synchronization issue in the loop. where is the right position to put the sigsuspend()?

#include <sys/types.h>
#include <sys/wait.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <signal.h>
#include <ctype.h>


pid_t pid2;
struct sigaction act;

sigset_t mask,oldmask,temp;

void sighandler(int signum, siginfo_t *info, void *ptr)
{
    printf("Received signal %d\n", signum);
    printf("Signal originates from process %lu\n",
        (unsigned long)info->si_pid);
        pid2 = info->si_pid;
}

int main(int argc,char **argv)
{
int i,j,counter = 0,counter2 = 0;
sigemptyset(&mask);
sigemptyset(&temp);
//sigemptyset(&oldmask);
sigaddset(&mask,SIGUSR1);

//sigset_t mask;

    memset(&act, 0, sizeof(act));
    act.sa_sigaction = sighandler;
    act.sa_flags = SA_SIGINFO;

    if(sigaction(SIGUSR1, &act, NULL) == -1)
        fprintf(stderr, "sigaction failed: %s\n", strerror(errno));


    pid_t current, pidOther;

    current = getpid();
    pidOther = atol(argv[1]);




int k;

for(k = 0;k < 100;k++){

if(pidOther != 0){ // second child
  kill(pidOther,SIGUSR1);
  sigprocmask(SIG_BLOCK,&mask,&oldmask);
  counter++;
  printf("2nd child = %d sent signal to 1st child = %d    signal number = %d\n",getpid(),pidOther,counter);
  //sigprocmask(SIG_BLOCK,&mask,&oldmask);
  sigsuspend(&temp);
}


if(pidOther == 0)  // fisrt child
{
   //pause();
   kill(pid2,SIGUSR1);
   sigprocmask(SIG_BLOCK,&mask,&oldmask); // was blank
   counter++;
   printf("\nj=%d  1st child = %d sent signal to 2nd child = %d    signal counter = %d\n",j,getpid(),pid2,counter);
   printf("test1\n");
   sigsuspend(&temp);  // was pause() 

  }

}

    return 0;

}

Answer 1

I don't see you calling fork() anywhere. Also taking the process ID of the second process is not the way your program should know about the child process. Here's a simple example of how to use fork.

pid_t pid = fork();
if (pid == 0)
{
    // executes only in child process..
    // do stuff related what you need to do in child process
}
else
{
    // executes only in parent process
    // pid variable contains the child process's PID.
    // do stuff related what you need to do in parent process
}

// runs in both parent and child.

Answer 2

问题在于，第一个孩子第一次循环时， pid2为0，因此它将信号发送到进程组中的每个进程（包括自身），这意味着它将立即开始循环，将信号（正好）发送回自身。 ..