有名管道

# 有名管道

有名管道（FIFO）存在于文件系统中，功能比无名管道强大，可以让无关联的进程交换数据。

# 有名管道创建函数

有名管道创建函数为mkfifo（与shell命令同名）。执行成功返回0，否则返回-1，并设置errno。

#include <sys/types.h>
#include <sys/stat.h>
int mkfifo(const char *pathname, mode_t mode)

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# 代码示例

// newfifo.c
#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
    mode_t mode = 0666;
    if(argc != 2) {
        puts("USAGE: newfifo {name}");
        exit(EXIT_FAILURE);
    }

    if((mkfifo(argv[1], mode)) < 0) {
        perror("mkfifo");
        exit(EXIT_FAILURE);
    }
    exit(EXIT_SUCCESS);
}

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# FIFO操作函数

打开FIFO管道：open
关闭FIFO管道：close
读取FIFO管道：read
写入FIFO管道：write

# 代码示例

# 有名管道的读程序

// readfifo.c
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <limits.h>

int main(void)
{
    int fd;    /* Descriptor for FIFO */
    int len;   /* Bytes read from FIFO */
    char buf[PIPE_BUF];
    mode_t mode = 0666;

    if((mkfifo("fifo1", mode)) < 0) {
        perror("mkfifo");
        exit(EXIT_FAILURE);
    }

    /* Open the FIFO read-only */
    if((fd = open("fifo1", O_RDONLY)) < 0) {
        perror("open");
        exit(EXIT_FAILURE);
    }
    /* Read and display the FIFO's output until EOF */
    while((len = read(fd, buf, PIPE_BUF - 1)) > 0)
        printf("rdfifo read: %s", buf);

    close(fd);

    exit(EXIT_SUCCESS);
}

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# 有名管道的写程序

/*
 * wrfifo.c - Write to a "well-known" FIFO
 */
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <limits.h>
#include <time.h>

int main(void)
{
    int fd;               /* Descriptor for FIFO */
    int len;              /* Bytes written to FIFO */
    char buf[PIPE_BUF];   /* Ensure atomic writes */
    time_t tp;            /* For time call */

    /* Identify myself */
    printf("I am %d\n", getpid());

    /* Open the FIFO write-only */
    if((fd = open("fifo1", O_WRONLY)) < 0) {
        perror("open");
        exit(EXIT_FAILURE);
    }

    /* Generate some data to write */
    while(1) {
        /* Get the current time */
        time(&tp);
        /* Create the string to write */
        len = sprintf(buf, "wrfifo %d sends %s", getpid(), ctime(&tp));
        /* 
        * Use (len + 1) because sprintf does not count
        * the terminating null
        */
        if((write(fd, buf, len + 1)) < 0) {
            perror("write");
            close(fd);
            exit(EXIT_FAILURE);
        }
        sleep(3);
    }

    close(fd);
    exit(EXIT_SUCCESS);
}

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# 输出

# 终端1
$ ./readfifo
rdfifo read: wrfifo 3591 sends Wed Feb 22 20:40:37 2023
rdfifo read: wrfifo 3591 sends Wed Feb 22 20:40:40 2023
rdfifo read: wrfifo 3591 sends Wed Feb 22 20:40:43 2023

#终端2
$ ./writefifo
I am 3591
^C

$ ls
fifo1  readfifo  writefifo

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# 分析

readfifo中创建一个命名管道名为fifo1，打开并阻塞读取管道内容，直到有其它进程向管道中写入内容。

writefifo中打开管道fifo1，循环向其中写入进程号和当前时间信息。

编辑

#Linux #进程间通信 #IPC

上次更新: 2023/03/31, 22:34:04

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