outline13.tr

unix/linux 编程实践一书的所有源代码

.sp 0.6i
.ft B
.tl ''Lecture \s8UDP\s0'Outline'
\l'6.5i'

.nf
.in +1i
.ta 1i +1.5i
\fBTopics\fR:  Multiple clients, servers with sensitive data

\fBApproach\fR:  Investigate license management in detail

\fBToday's New Ideas\fR:  datagrams, the ticket model, transactions

.ta 0.5i +0.5i +0.5i
\fBOutline\fR

	The Ideal World - Where systems never crash
	
		1.  What is a product license
			A means for controlling where/who/how many users

		2.  What is a license server
			A program that enforces product licensing in
			a multi-user setting.

		3.  The ticket model
			How the license server limits usage of an
			application

		4.  The Communication Model
			Simple transactions - a request and a response
			Datagrams - postcards from one socket to another
	
		5.  Flow of Control
			In the client
			In the Server

		6.  The code itself.

	The Real World - where bad things can happen to good programs

	Possible problems:
		1.  Clients can crash - natural disasters
		2.  Servers can crash - unnatural disasters.

	Solutions:
		1.  Clients who crash leave tickets stuck - server
			can "expire" these tickets.
		    - The ball_move() model for ticket expiration.

		2.  When the server crashes, the database is lost.
		   - The clients can "check in" to be sure their tickets
			are still good.
		   - Ticket validation as a means of recovery.