Linux进程间通信-FIFO(命名管道)

转载自：http://blog.csdn.net/a1009563517/article/details/47079883
与无名管道不同，FIFO可用于无关系的进程之间
1.管道读写端操作，如果读写端有一方读或写没打开，则另一端阻塞直到打开（非阻塞情况下会成功打开）
2.如果管道buf满了没有剩余空间，则写端会阻塞直到管道有pipe_buf的空间（如果管道是以非阻塞打开的，则空间满了继续写那么出错返回）
3.读段会一直阻塞直到写端向读端写入数据（非阻塞情况下出错返回）
4.多个读段去读，如果读的buf小于PIPE_BUF则读取操作时原子操作，如果buf>PIPE_BUF则读取操作是非原子的，读取出来的数据是混乱的直至最后一个访问管道的进程结束，内存里的管道数据会被删除，但是管道还在

int main()  
{  FILE                    * b_fd;  int                       b_ret, b_num = 0;  char                    * b_fifo_name = "/tmp/fifo";  pid_t                     b_pid[10];  unlink(b_fifo_name);  b_ret = mkfifo(b_fifo_name, 0777);  if(b_ret < 0)  {  printf("mkfifo fail line = %d, fun = %s, file = %s", __LINE__, __func__, __FILE__);  return -1;  }  b_pid[b_num] = fork();  if(b_pid[b_num] < 0)  {  return -1;  }  if(0 == b_pid[b_num])  {  /*子线程*/  ipc_pipe_fun1();  }  b_num++;  b_pid[b_num] = fork();  if(b_pid[b_num] < 0)  {  return -1;  }  if(0 == b_pid[b_num])  {  /*子线程*/  ipc_pipe_fun1();  }  b_num++;  b_pid[b_num] = fork();  if(b_pid[b_num] < 0)  {  return -1;  }  if(0 == b_pid[b_num])  {  /*子线程*/  ipc_pipe_fun2();  }  b_num++;  while(1)  {  sleep(10000);  }  return 0;  
}  int ipc_pipe_fun1()  
{  int       b_ret = 0, b_ttl = 0;  char      b_buf[4098];  int       b_fd = open("/tmp/fifo", O_RDONLY|O_NONBLOCK);  while(1)  {  memset(b_buf, 0, sizeof(b_buf));  b_ret = read(b_fd, b_buf, 100);  printf("b_ret = %d, b_buf = %s\n", b_ret, b_buf);  }  return 0;  
}  int ipc_pipe_fun2()  
{  int     b_ret;  char    b_buf[100];  int     b_num = 0, b_len = 0, b_ttl = 0;  char  * b_mall = (char *)malloc(65535);  int     b_fd = open("/tmp/fifo", O_WRONLY|O_NONBLOCK);  while(1)  {  memset(b_buf, 0, sizeof(b_buf));  sprintf(b_buf, "%d|", b_num);  b_num = (++b_num)%1000000;  printf("==================\n");  b_len = write(b_fd, b_buf, 100);  b_ttl += b_len;  printf("b_ttl = %d, b_len = %d, b_buf = %s\n", b_ttl, b_len, b_buf);  }  return 0;  
}