c - 通过fifo向服务器发送确认消息来区分客户端，客户端不会收到后续消息

Question

我有一个服务器和两个不同的客户端。服务器和客户端将通过 FIFO 进行通信。每个客户端首先向服务器发送一个包含 clientpid 和数字的结构变量。数字用于区分客户。然后服务器为每个客户端创建足够的 fifo。建立此后，服务器向每个客户端发送不同的消息。当我运行服务器和客户端时，客户端没有收到消息，它们卡在读取状态。为什么会发生这种情况以及我应该采取什么措施来解决它？ (对于这个例子，我简化了客户端，它们几乎是相同的，除了它们传递给服务器以区分自己的数字。在原始程序中，两个客户端将做不同的事情，并且它们将从服务器接收不同的数据，这就是为什么我需要区分它们。)

服务器.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <assert.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <sys/un.h>
#include <stdint.h>
#include <sys/time.h>
#include <arpa/inet.h>
#include <fcntl.h>


#define ec_neg1(s,m) if((s) == -1) {perror(m); exit(errno);}

#define SERVER_FIFO_NAME "fifo_server"
#define PERM_FILE        0664

struct acknow_
{
 pid_t clientpid;
 int num;
};


int make_fifo_name(pid_t pid, char *name, size_t name_max)
{
 snprintf(name, name_max, "fifo%ld", (long)pid);
 return 0;
} 


int main()
{
 int fd_server;
 int fd_send;
 int fd_recv;
 ssize_t nread;
 struct acknow_ acknow;

 char fifo_send[100];
 char fifo_recv[100];

 char msg1[100] = "SENDER GOT THE MESSAGE\n";
 char msg2[100] = "RECEIVER GOT THE MESSAGE\n";

 printf("server is started\n");

 if(mkfifo(SERVER_FIFO_NAME, PERM_FILE) == -1 && errno != EEXIST)
  {perror("can't make fifo"); exit(errno); }

  ec_neg1( fd_server = open(SERVER_FIFO_NAME, O_RDWR), "cant open fd_server" )

  while(1)
  {
    ec_neg1( nread = read(fd_server, &acknow, sizeof(acknow)), "can't read from fd_server")
    if (nread == 0) 
    {
      errno = ENETDOWN;
      perror("nread == 0"); exit(errno);
    }

    if(acknow.num == 1) /* sender's pid arrived first */
    {

      /*MAKE FIFO OF THE SENDER*/
      make_fifo_name(acknow.clientpid, fifo_send, sizeof(fifo_send));

      ec_neg1(fd_send = open(fifo_send, O_WRONLY), "can't open fifo_send" )

      /*GET PID OF THE RECEIVER*/  
      ec_neg1( nread = read(fd_server, &acknow, sizeof(acknow)), "can't read from fd_server")

      if (nread == 0) 
      {
        errno = ENETDOWN;
        perror("nread == 0"); exit(errno);
      }


      /*MAKE FIFO OF THE RECEIVER*/
      make_fifo_name(acknow.clientpid, fifo_recv, sizeof(fifo_recv));

      ec_neg1( fd_recv = open(fifo_recv, O_WRONLY), "can't open fifo_recv" )

    }
    else /* receiver's pid arrived first */
    {

      /*MAKE FIFO OF THE SENDER*/
      make_fifo_name(acknow.clientpid, fifo_recv, sizeof(fifo_recv));

      ec_neg1(fd_recv = open(fifo_recv, O_WRONLY), "can't open fifo_recv" )

      /*GET PID OF THE RECEIVER*/  
      ec_neg1( nread = read(fd_server, &acknow, sizeof(acknow)), "can't read from fd_server")

      if (nread == 0) 
      {
        errno = ENETDOWN;
        perror("nread == 0"); exit(errno);
      }

      /*MAKE FIFO OF THE RECEIVER*/
      make_fifo_name(acknow.clientpid, fifo_send, sizeof(fifo_send));

      ec_neg1( fd_send = open(fifo_send, O_WRONLY), "can't open fifo_name" )


    }

    printf("sending message to sender\n");
    ec_neg1( write(fd_send, &msg1, sizeof(msg1)), "can't write to fd_send" )
    printf("sending message to receiver\n");
    ec_neg1( write(fd_recv, &msg2, sizeof(msg2)), "can't write to fd_recv")

    ec_neg1( close(fd_send), "can't close fd_send" )
    ec_neg1( close(fd_recv), "can't close fd_recv" )

    printf("done\n");
 }

  ec_neg1( close(fd_server), "can't close fd_server" ) 



 return 0;
}

Client1.c(这里我只发布Client1，Client2只是相同的代码，如果你想运行它们，只需将“acknow.num”更改为“2”即可。)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <assert.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <sys/un.h>
#include <stdint.h>
#include <sys/time.h>
#include <arpa/inet.h>
#include <fcntl.h>



#define ec_neg1(s,m) if((s) == -1) {perror(m); exit(errno);}

#define SERVER_FIFO_NAME "fifo_server"
#define PERM_FILE        0664


struct acknow_
{
 pid_t clientpid;
 int num;
};


int make_fifo_name(pid_t pid, char *name, size_t name_max)
{
snprintf(name, name_max, "fifo%ld", (long)pid);
return 0;
}


int main()
{

int fd_server, fd_client;
ssize_t nread;
char fifo_name[100];
char msg[100];
struct acknow_ acknow;


printf("client1 started\n");

acknow.clientpid = getpid();
acknow.num = 1;


make_fifo_name(acknow.clientpid, fifo_name, sizeof(fifo_name));

if (mkfifo(fifo_name, PERM_FILE) == -1 && errno != EEXIST)
  {perror("can't make fifo"); exit(errno); }

ec_neg1( fd_server = open(SERVER_FIFO_NAME, O_WRONLY), "can't open fd_server" )

ec_neg1( write(fd_server, &acknow, sizeof(acknow)),"can't write to fd_server" )

ec_neg1( fd_client = open(fifo_name, O_RDWR), "can't open fifo_name"  )


while((nread = read(0, &msg, sizeof(msg))))
{

  write(1, msg, nread);

}

if (nread == 0) 
{
  errno = ENETDOWN;
  perror("nread == 0"); exit(errno);
}
if (nread == -1) 
 perror("can't read"); exit(errno);



 ec_neg1( close(fd_server), "can't close fd_server" )
 ec_neg1( close(fd_client), "can't close fd_client" )
 ec_neg1( unlink(fifo_name), "can't unlink fifo_name" )


 return 0;
}

Answer 1

首先，在服务器中，您打开读取 FIFO O_WRONLY。这应该是O_RDONLY。

其次，在客户端中，您将打开读取 FIFO O_RDWR。我相信这是 POSIX 下未定义的行为(您没有提到操作系统)，应该是 O_RDONLY。这足以继续下去。