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: W当 安全模式（safe mode） 被激活，PHP 将检查您将要操作的目录和正在执行的脚本是否有相同的 UID。