unix 网络编程卷2 第43页 管道：open竟然会阻塞？

创建fifo管道的时候，open会阻塞？
还是我的代码有问题？

1. #include <stdio.h>
2. #include <unistd.h>
3. #include <fcntl.h>
4. #include <errno.h>
5. #include <sys/types.h>
6. #Include <sys/stat.h>
7. #define FIFO1 "/tmp/fifo.1"
8. #define FIFO2 "/tmp/fifo.2"
9. #define FILE_MODE (S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)
10. int main()
11. {
12. int rfd, wfd;
13. if ((mkfifo(FIFO1, FILE_MODE) < 0) && errno != EEXIST)
14. {//error
15. exit(0);
16. }
17. if ((mkfifo(FIFO2, FILE_MODE) < 0) && errno != EEXIST)
18. {//error
19. exit(0);
20. }
21. fprintf(stderr, "before open\n");
22. rfd = open(FIFO1, O_RDONLY, 0);
23. wfd = open(FIFO2, O_WRONLY, 0);
24. fprintf(stderr, "after open\n");
25. //到这里出现问题，after open一直没有打印出来。
26. }

man 3 open.一般3的解释较2的解释详细.

1. O_NONBLOCK
2. When opening a FIFO with O_RDONLY or O_WRONLY set:
3. * If  O_NONBLOCK  is set, an open() for reading-only shall return without delay. An open() for writing-only shall return an error if no process currently has the file open for reading.
4. * If O_NONBLOCK is clear, an open() for reading-only shall block the calling thread until  a  thread  opens  the  file for writing. An open() for writing-only shall block the calling thread until a thread opens the  file for reading.

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