linux系统编程之fifo

序言

mkfifo用于创建有名管道(named pipe)，在文件系统中以管道文件的形式存在
所以可用于进程与进程间，线程与线程间通信

管道特点：
1.有收发双方才能建立通信
2.收发阻塞

代码

fifo_server.c

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#define SERVER_FIFO            "/tmp/fifo_common"
#define CLIENT_FIFO_TEMPLATE   "/tmp/fifo_client.%ld"
#define CLIENT_FIFO_NAME_LEN   (sizeof(CLIENT_FIFO_TEMPLATE) + 20)

#define DEBUG_MSG(msg) do{ \
    fprintf(stdout,"[file:%s],[function:%s],[line:%d],%s\n",__FILE__,__FUNCTION__,__LINE__,msg); \
}while(0);

// client->server
struct request
{
    pid_t pid;
    int requset_num;
};

// server->client
struct response
{
    int response_num;
};

int main(int argc, char *argv[])    
{
    char client_fifo[CLIENT_FIFO_NAME_LEN];
    int server_fd;
    int client_fd;
    int dummy_fd;
    struct request req;
    struct response res;
    
    umask(0);

    if (-1 == mkfifo(SERVER_FIFO, S_IRUSR | S_IWUSR | S_IWGRP) && errno != EEXIST)
    {
        DEBUG_MSG("mkfifo error");
        exit(EXIT_FAILURE);
    }

    if (-1 == (server_fd = open(SERVER_FIFO, O_RDONLY)))
    {
        DEBUG_MSG("open error");
        exit(EXIT_FAILURE);
    }

    if (-1 == (dummy_fd = open(SERVER_FIFO, O_RDONLY)))
    {
        DEBUG_MSG("open error");
        exit(EXIT_FAILURE);
    }

    if (SIG_ERR == signal(SIGPIPE, SIG_IGN))
    {
        DEBUG_MSG("signal error");
        exit(EXIT_FAILURE);
    }

    for (;;)
    {
        if (read(server_fd, &req, sizeof(struct request)) != sizeof(struct request))
        {
            DEBUG_MSG("error reading request, discarding");
            continue;
        }

        printf("server: client-pid = %ld\n", req.pid);

        snprintf(client_fifo, CLIENT_FIFO_NAME_LEN, CLIENT_FIFO_TEMPLATE, (long)req.pid);

        if (-1 == (client_fd = open(client_fifo, O_WRONLY)))
        {
            DEBUG_MSG("open client error, continue");
            continue;
        }

        res.response_num = req.requset_num + 1;
        
        if (write(client_fd, &res, sizeof(struct response)) != sizeof(struct response))
            DEBUG_MSG("write to client error");

        if (-1 == close(client_fd))
            DEBUG_MSG("close client fd error");
    }

    exit(EXIT_SUCCESS);
}

fifo_client.c

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#define SERVER_FIFO            "/tmp/fifo_common"
#define CLIENT_FIFO_TEMPLATE   "/tmp/fifo_client.%ld"
#define CLIENT_FIFO_NAME_LEN   (sizeof(CLIENT_FIFO_TEMPLATE) + 20)

#define DEBUG_MSG(msg) do{ \
    fprintf(stdout,"[file:%s],[function:%s],[line:%d],%s\n",__FILE__,__FUNCTION__,__LINE__,msg); \
}while(0);

// client->server
struct request
{
    pid_t pid;
    int requset_num;
};

// server->client
struct response
{
    int response_num;
};

static char client_fifo[CLIENT_FIFO_NAME_LEN];

static void remove_fifo(void)
{
    unlink(client_fifo);
}

int main(int argc, char *argv[])    
{
    int server_fd;
    int client_fd;
    struct request req;
    struct response res;
    
    umask(0);

    snprintf(client_fifo, CLIENT_FIFO_NAME_LEN, CLIENT_FIFO_TEMPLATE, (long)getpid());

    if (-1 == mkfifo(client_fifo, S_IRUSR | S_IWUSR | S_IWGRP) && errno != EEXIST)
    {
        DEBUG_MSG("mkfifo error");
        exit(EXIT_FAILURE);
    }

    if (0 != atexit(remove_fifo))
        DEBUG_MSG("atexit error");
    
    req.pid = getpid();
    req.requset_num = 9;

    if (-1 == (server_fd = open(SERVER_FIFO, O_WRONLY)))
    {
        DEBUG_MSG("open error");
        exit(EXIT_FAILURE);
    }

    if (write(server_fd, &req, sizeof(struct request)) != sizeof(struct request))
        DEBUG_MSG("write to server error");
        
    if (-1 == (client_fd = open(client_fifo, O_RDONLY)))
    {
        DEBUG_MSG("open client error");
        exit(EXIT_FAILURE);
    }

    if (read(client_fd, &res, sizeof(struct response)) != sizeof(struct response))
    {
        DEBUG_MSG("error reading response \n");
        exit(EXIT_FAILURE);
    }
    
    printf("%d\n", res.response_num);

    exit(EXIT_SUCCESS);
}