Therefore, it is not defined that it cannot have special sessions such as MSGBOX. Just because it runs in the background and cannot be reached by front-end users, sessions such as MSGBOX are meaningless. While MSGBOX and others may even block the normal operation of the program, so the background effect will not be achieved. Although it stops there for processing due to an error, the front-end user cannot know and interact with it, which violates the rules of the background operating program, and there is no exception prompt in the view of the front-end user during this period, Even if it is considered to be in normal operation, it will wait until the background administrator handles the exception. Such waiting also wastes a lot of unnecessary time.
Web programs are divided into foreground programs and background programs. Most websites need background programs, among which background programs are for convenience Webmaster Make management changes. 
