A cooperating process is one that can affect or be affected by other processes executing in a 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 threads, discussed in Chapter 4. Concurrent access to shared data may result in data inconsistency, however. 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.
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 can be used to enable processes to share memory.
Let's return to our consideration of the bounded buffer. As we pointed out, our original solution allowed at most
BUFFER_SIZE − 1 items in the buffer at the same time. Suppose we want to modify the algorithm to ...