A new solution to the mutual exclusion problem is presented that, in the absence of contention, requires only seven memory accesses. It assumes atomic reads and atomic writes to shared registers. Capsule Review To build a useful computing system from a collection of processors that communicate by sharing memory, but lack any atomic operation more complex than a memory read or write, it is necessary to implement mutual exclusion using only these operations. Solutions to this problem have been known for twenty years, but they are linear in the number of processors. Lamport presents a new algorithm which takes constant time (five writes and two reads) in the absence of contention, which is the normal case. To achieve this performance it sacrifices fairness, which is probably unimportant in practical applications. The paper gives an informal argument that the algorithm's performance in the absence of contention is optimal, and a fairly formal proof of safety and freedom from deadlock, u...

Formal specifications of operating system interfaces can be a useful part of their documentation. We illustrate this by documenting the Threads synchronization primitives of the Taos operating system. We start with an informal description, present a way to formally specify interfaces in concurrent systems, and then give a formal specification of the synchronization primitives. We briefly discuss both the implementation and what we have learned from using the specification for more than a year. Our main conclusion is that programmers untrained in reading formal specifications have found this one helpful in getting their work done. iii Introduction The careful documentation of interfaces is an important step in the production of software upon which other software is to be built. If people are to use software without having to understand its implementation, documentation must convey semantic as well as syntactic information. When the software involves concurrency, adequate documentatio...

ultiprocessors, especially those constructed of relatively low-cost microprocessors, offer a cost-effective solution to the continually increasing need for computing power and speed. These systems can be designed either to maximize the throughput of many jobs or to speed up the execution of a single job; they are respectively called throughput-oriented and speeduporiented multiprocessors. In the first type of system, jobs are distinct from each other and execute as if they were running on different uniprocessors. In the second type an application is partitioned into a set

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Since the very beginning of hardware development, computer processors were invented with ever-increasing clock frequencies and sophisticated in-build optimization strategies. Due to physical limitations, this ’free lunch ’ of speedup has come to an end. The following article gives a summary and bibliography for recent trends and challenges in CMP architectures. It discusses how 40 years of parallel computing research need to be considered in the upcoming multi-core era. We argue that future research must be driven from two sides- a better expression of hardware structures, and a domain-specific understanding of software parallelism. 1