Operating System Concepts, Seventh Edition

Chapter 6. Process Synchronization

A cooperating process is one that can affect or be affected by other processes executing in the system. Cooperating processes can either directly share a logical address space (that is, both code and data) or be allowed to share data only through files or messages. The former case is achieved through the use of lightweight processes or threads, which we discussed in Chapter 4. Concurrent access to shared data may result in data inconsistency. In this chapter, we discuss various mechanisms to ensure the orderly execution of cooperating processes that share a logical address space, so that data consistency is maintained.

CHAPTER OBJECTIVES

• To introduce the critical-section problem, whose solutions can be used to ensure the consistency of shared data.

• To present both software and hardware solutions of the critical-section problem.

• To intoduce the concept of atomic transaction and describe mechanisms to ensure atomicity.

Background

In Chapter 3, we developed a model of a system consisting of cooperating sequential processes or threads, all running asynchronously and possibly sharing data. We illustrated this model with the producer-consumer problem, which is representative of operating systems. Specifically, in Section 3.4.1, we described how a bounded buffer could be used to enable processes to share memory.

Let us return to our consideration of the bounded buffer. As we pointed out, our solution allows at most BUFFER.SIZE — 1 items in the buffer at the ...