FIFO具名/命名管道
(匿名)管道应用的一个限制就是只能在具有共同祖先(具有亲缘关系)的进程间通信。
如果我们想在不相关的进程之间交换数据,可以使用FIFO文件来做这项工作,它经常被称为命名管道;命名管道是一种特殊类型的文件.
创建一个命名管道
1)命名管道可以从命令行上创建:
$mkfifo<filename>
2)命名管道在程序里创建:
#include <sys/types.h>#include <sys/stat.h>int mkfifo(const char *pathname, mode_t mode);//示例int main(){if (mkfifo("p2", 0644) == -1)err_exit("mkfifo error");}
FIFO与PIPE的区别:
1)匿名管道由pipe函数创建并打开。
命名管道由mkfifo函数创建,打开用open
2)FIFO(命名管道)与pipe(匿名管道)之间唯一的区别在它们创建与打开的方式不同,一但这些工作完成之后,它们具有相同的语义 (TheonlydifferencebetweenpipesandFIFOsisthemannerinwhichtheyarecreatedandopened.
Oncethesetaskshavebeenaccomplished,I/OonpipesandFIFOshasexactlythesamesemantics.)。
命名管道的打开规则
1)读打开FIFO
O_NONBLOCKdisable(阻塞):阻塞直到有相应进程为写而打开该FIFO
O_NONBLOCKenable(非阻塞):立刻返回成功
//示例1: 阻塞, 只读打开int main(){int fd = open("fifo", O_RDONLY);if (fd == -1)err_exit("FIFO open error");cout << "fifo O_RDONLY open success" << endl;}//示例2: 只读, 非阻塞打开int main(){int fd = open("fifo", O_RDONLY|O_NONBLOCK);if (fd == -1)err_exit("FIFO open error");cout << "fifo O_RDONLY open success" << endl;}
2)写打开FIFO
O_NONBLOCKdisable(阻塞):阻塞直到有相应进程为读而打开该FIFO
O_NONBLOCKenable(非阻塞):立刻返回失败,,错误码为ENXIO
//示例1: 阻塞, 只写打开int main(){int fd = open("fifo", O_WRONLY);if (fd == -1)err_exit("FIFO open error");cout << "FIFO O_WRONLY open success" << endl;}//示例2: 非阻塞, 只写打开int main(){int fd = open("fifo", O_WRONLY|O_NONBLOCK);if (fd == -1)err_exit("FIFO open error");cout << "FIFO O_WRONLY open success" << endl;}
命名管道的读写规则
同匿名管道
/**FIFO示例, 两个进程通过FIFO对拷数据:利用管道,两个进程间进行文件复制。1.进程writefifo:(1)读文件(文件名从命令行参数中获取)(2)写入管道myFifo(管道由该进程创建)(3)关闭文件及管道2.进程readfifo:(1)读管道myFifo(2)写入文件[该文件有进程创建并打开](3)关闭文件(4)删除管道*///1:writefifoint main(int argc, char *argv[]){if (argc < 2)err_quit("Usage: ./writefifo <read-file-name>");// 创建管道if (mkfifo("myFifo", 0644) == -1)err_exit("mkfifo error");int outfd = open("myFifo", O_WRONLY); //打开FIFOint infd = open(argv[1], O_RDONLY);//打开文件if (outfd == -1 || infd == -1)err_exit("open file/fifo error");char buf[BUFSIZ];int readBytes;while ((readBytes = read(infd, buf, sizeof(buf))) > 0){write(outfd, buf, readBytes);}close(infd);close(outfd);}//2:readfifoint main(int argc, char *argv[]){if (argc < 2)err_quit("Usage: ./writefifo <write-file-name>");int outfd = open(argv[1], O_WRONLY|O_CREAT|O_TRUNC, 0644); //创建并打卡文件int infd = open("myFifo", O_RDONLY); //打开FIFOif (infd == -1 || outfd == -1)err_exit("open file/fifo error");char buf[BUFSIZ];int readBytes;while ((readBytes = read(infd, buf, sizeof(buf))) > 0){write(outfd, buf, readBytes);}close(outfd);unlink("myFifo"); //删除FIFO}
然后继续努力,把让自己跌倒的石头搬掉或绕过去,不就解决问题了吗