posix_mkfifo() creates a special FIFO file which exists in the file system and acts as a bidirectional communication endpoint for processes.
The second parameter mode has to be given in octal notation (e.g. 0644). The permission of the newly created FIFO also depends on the setting of the current umask(). The permissions of the created file are (mode & ~umask).
如果成功则返回 TRUE，失败则返回 FALSE。
注: 当安全模式被激活时，PHP 将检查被操作的目录是否和正在执行的脚本有相同的 UID（所有者）。