linux编程之pipe()函数

/*
 * 有亲缘关系的进程间的fifo的使用
 * fifo 使用的简单例子
 */

#include "../all.h"

#define FIFO_PATH "/tmp/hover_fifo"


void 
do_sig(int signo)
{
    if (signo == SIGCHLD)
        while (waitpid(-1, NULL, WNOHANG) > 0)
            ;
}



int
main(void)
{
    int ret;
    int fdr, fdw;
    pid_t pid;

    char words[10] = "123456789";
    char buf[10] = {‘\0‘};    
    
    // 创建它,若存在则不算是错误,
    // 若想修改其属性需要先打开得到fd,然后用fcntl来获取属性,然后设置属性.

    if (((ret = mkfifo(FIFO_PATH, FILE_MODE)) == -1) 


                     && (errno != EEXIST))
        perr_exit("mkfifo()");
    fprintf(stderr, "fifo : %s created successfully!\n", FIFO_PATH);

    signal(SIGCHLD, do_sig);

    pid = fork();
    if (pid == 0) { // child

        if ((fdr = open(FIFO_PATH, O_WRONLY)) < 0) // 打开fifo用来写
            perr_exit("open()");
        sleep(2);

        // 写入数据
        if (write(fdr, words, sizeof(words)) != sizeof(words)) 
            perr_exit("write");
        fprintf(stderr, "child write : %s\n", words);
        close(fdw);
    } else if (pid > 0) { // parent

        if ((fdr = open(FIFO_PATH, O_RDONLY)) < 0) // 打开fifo用来读

            perr_exit("open()");

        fprintf(stderr, "I father read, waiting for child ...\n");
        if (read(fdr, buf, 9) != 9) //读数据
            perr_exit("read");

        fprintf(stderr, "father get buf : %s\n", buf);
        close(fdr);
    }
    // 到这里fifo管道并没有被删除,必须手动调用函数unlink或remove删除.

    return 0;    
}



/*
 * FIFO server
 */

#include "all.h"

int
main(void)
{
    int fdw, fdw2;
    int fdr;
    char clt_path[PATH_LEN] = {‘\0‘};
    char buf[MAX_LINE] = {‘\0‘};
    char *p;
    int n;
    
    if (mkfifo(FIFO_SVR, FILE_MODE) == -1 && errno != EEXIST)    
        perr_exit("mkfifo()");    
    if ((fdr = open(FIFO_SVR, O_RDONLY)) < 0)    
        perr_exit("open()");
    /* 
     * 根据fifo的创建规则, 若从一个空管道或fifo读, 


     * 而在读之前管道或fifo有打开来写的操作, 那么读操作将会阻塞 
     * 直到管道或fifo不打开来读, 或管道或fifo中有数据为止. 


     *


     * 这里,我们的fifo本来是打开用来读的,但是为了,read不返回0,

     * 让每次client端读完都阻塞在fifo上,我们又打开一次来读.
     * 见unpv2 charper 4.7
     */
    if ((fdw2 = open(FIFO_SVR, O_WRONLY)) < 0)    
        fprintf(stderr, "open()");
    
    while (1) {
        /* read client fifo path from FIFO_SVR */


     /* 这里由于FIFO_SVR有打开来写的操作,所以当管道没有数据时, 


      * read会阻塞,而不是返回0. 


      */
        if (read(fdr, clt_path, PATH_LEN) < 0) {
            fprintf(stderr, "read fifo client path error : %s\n", strerror(errno));    
            break;
        }
        if ((p = strstr(clt_path, "\r\n")) == NULL) {
            fprintf(stderr, "clt_path error: %s\n", clt_path);
            break;
        }
        *p = ‘\0‘;
        DBG("clt_path", clt_path);
        if (access(clt_path, W_OK) == -1) { // client fifo ok, but no permission

            perror("access()");    
            continue;
        }
        /* open client fifo for write */
        if ((fdw = open(clt_path, O_WRONLY)) < 0) {
            perror("open()");    
            continue;
        }
        if ((n = read(fdr, buf, WORDS_LEN)) > 0) { /* read server words is ok */
            printf("server read words : %s\n", buf);
            buf[n] = ‘\0‘;
            write(fdw, buf, strlen(buf));    
        }
    }
    
    close(fdw);    
    unlink(FIFO_SVR);
    exit(0);
}

/*
 * Fifo client
 *
 */
#include "all.h"



int
main(void)
{
    int fdr, fdw;
    pid_t pid;    
    char clt_path[PATH_LEN] = {‘\0‘};
    char buf[MAX_LINE] = {‘\0‘};
    char buf_path[MAX_LINE] = {‘\0‘};
    
    snprintf(clt_path, PATH_LEN, FIFO_CLT_FMT, (long)getpid());        
    DBG("clt_path1 = ", clt_path);
    snprintf(buf_path, PATH_LEN, "%s\r\n", clt_path);

    if (mkfifo(clt_path, FILE_MODE) == -1 && errno != EEXIST)    
        perr_exit("mkfifo()");

    /* client open clt_path for read
     * open server for write 
       */
    if ((fdw = open(FIFO_SVR, O_WRONLY)) < 0) 
        perr_exit("open()");
    
    /* write my fifo path to server */    
    if (write(fdw, buf_path, PATH_LEN) != PATH_LEN)        
        perr_exit("write()");
    if (write(fdw, WORDS, WORDS_LEN) < 0)    /* write words to fifo server */
        perr_exit("error");

    if ((fdr = open(clt_path, O_RDONLY)) < 0)    
        perr_exit("open()");
    if (read(fdr, buf, WORDS_LEN) > 0) {     /* read reply from fifo server */
        buf[WORDS_LEN] = ‘\0‘;
        printf("server said : %s\n", buf);
    }
    
    close(fdr);
    unlink(clt_path);
    
    exit(0);
}