COP 5611, Operating Systems, Spring, 2003

Department of Computer Science, Florida State University

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**Points: 100**

**Due: Thursday, February 20, 2003**

**Problem 5 (45 points)** A distributed system consists
of three processes given by the following diagram. The system uses vector
clocks with initial values of zeros in all entries. Each dot in the diagram
represents an event.

(1)
(**10 points**) Show the vector clocks of the sending and
receiving events of all the messages without casual ordering of messages.

(Thanks to Brian Bouta)

(2)
(**10 points**) Give the message pairs whose sending events
are causally related based on their timestamps.

(Thanks to Brian Bouta)

(3)
(**25 points**) Apply the Schiper-Eggli-Sandoz algorithm to
the system. You need to show the ordered pairs before and after each message is
sent and the vector clock of the receiving process right before the message is
being received. For each message’s receiving event, use the algorithm to show
whether it can be delivered immediately or needs to be buffered. In the latter
case (being buffered), show when and why the message can be delivered.

(Thanks to Qiang Zhang)