linux编程之pipe()函数详解

#include

int pipe(int filedes[2]);

#include 

    #include 

   int mkfifo(const char *pathname, mode_t mode);

/*
 * 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);
}