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).
成功回傳TRUE失敗回傳FALSE。
備注:當安全模式開啟,PHP會檢查執行的腳本和要操作的檔案或目錄是否有相同的UID(擁有者)