c - 两个子进程通过命名管道进行通信

Question

我有一个主程序，它创建两个子进程和一个命名管道(FIFO)。每个子进程通过 execv() 执行一个名为“sendSignal”的程序。“sendSignal”的参数之一是主程序中的 FIFO。

children 将互相发送信号。它通过主程序(在变量firstShooter中)中的一个参数来决定哪个信号首先射击。

我想知道这两个 child 如何通过这个命名管道向对方发送他们的 pid。

主程序如下:

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

/* this program should be provided with 2 arguments */

int main(int argc, char **argv)
{

   char str1[15];
   char str2[15];
   char fileDescriptor[15];
   char *my_args[4];
   char *myfifo = "myfifo";

  int fd, pipeCheck;
  pid_t pid1, pid2, wid;


  /* If the user does not provide the argument to determin which child is firing first */
  if(argc != 2)
  {
    fprintf(stderr,"%s: 2 arguments needed, got %d\n",argv[0],argc-1);
    exit(1);
  }

  /* create the FIFO (named pipe) */
  pipeCheck = mkfifo(myfifo, 0666);

   /* check if the named pipe was created properly if not output an error */
   if(pipeCheck == -1)
   {
     fprintf(stderr, "%s: Error creating named pipe: %s\n",argv[0], strerror(errno));
      exit(1);    
   }


   pid1 = fork();

   if (pid1 < 0)
    {
      fprintf(stderr, ": fork failed: %s\n", strerror(errno));
      exit(1);
    }

    if(pid1 == 0)
    {


      my_args[0] = "sendSignal";
      my_args[1] = argv[1];
      my_args[2] = myfifo; //  the named pipe as arguemnt
      my_args[3] = NULL;
      execv("sendSignal",my_args);
      fprintf(stderr,"sendSignal cannot be executed by first child...");
      exit(-1);
    }


     pid2 = fork();

    if(pid2 < 0)
    {
       fprintf(stderr, ": fork failed: %s\n", strerror(errno));
       exit(1);
    }

    if(pid2 == 0)
    {

      my_args[0] = "sendSignal";
      my_args[1] = argv[1];
      my_args[2] = myfifo;  // named pipe as arguemnt
      my_args[3] = NULL; 
     // printf("this is converted = %s\n",my_args[1]);
      execv("sendSignal",my_args);
      fprintf(stderr,"sendSignal cannot be executed by second child...");
      exit(-1);
    }

close(fd);
unlink(myfifo);


wid = wait(NULL);


return 0;

}

这是发送信号:

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


void sig_handler(int signo)
{
    if(signo == SIGUSR1)
        printf("signal received\n");

}

int main(int argc, char **argv)
{

     char abspath[256] = "";
     getcwd(abspath, 256);
     strrchr(abspath, '/');

     if(signal(SIGUSR1,sig_handler) == SIG_ERR)
        printf("\n Cannot catch the signal\n");

     char *myfifo = "myfifo";

     int firstShooter = atoi(argv[1]);  //define the first process to send the signal 

     int fd;
     char str1[15];
     char str2[15];
     char pid1[15];
     char pid2[15];

     fd = open(argv[2],O_RDWR);


     if(firstShooter == 1)
     {
        sprintf(pid1,"%d",getpid());
        write(fd,pid1,sizeof(pid1));
     }

     if(firstShooter == 2)
     {
        sprintf(pid2,"%d",getpid());
        write(fd,pid2,sizeof(pid2));
     }


     read(fd,str1,sizeof(str2));
     read(fd,str2,sizeof(str2));

    close(fd);

    printf("str1 = %s\n",str1);
    printf("str2 = %s\n",str2);


    return 0;
}

Answer 1

您的两个子进程都有相同的参数:

my_args[0] = "sendSignal";
my_args[1] = argv[1];
my_args[2] = myfifo; //  the named pipe as argument
my_args[3] = NULL;

firstShooter 参数没有意义，因为进程无法将自己标识为第一或第二。

我建议再加一个参数——进程索引。 sendSignal 函数逻辑可以这样修改:

char pid1[15];
char pid2[15];
int processIndex = atoi(argv[3]);

fd = open(argv[2],O_RDWR);

if (processIndex == firstShooter)
{
  // Send firstShooter PID
  sprintf(pid1,"%d",getpid());
  write(fd,pid1,sizeof(pid1));

  // Got the other PID
  read(fd,pid2,sizeof(pid2));
}
else
{
  // Got the firstShooter PID
  read(fd,pid1,sizeof(pid1));

  // Send the other PID
  sprintf(pid2,"%d",getpid());
  write(fd, pid2, sizeof(pid2));
}

close(fd);

printf("pid1 = %s\n",pid1);
printf("pid2 = %s\n",pid2);