Abstract

All analyss s made of the shared memory reqmrements for tmplemelltllg mutual exclusmon of N asynchronous parallel processes m a model where the only primitive communication mechamsm is a general test-and-set operatmn on a smgle shared variable. Whde two variable values suffice to tmplement simple mutual exclusion wthout deadlock, tt is shown that any soluuon whtch avoids possible lockout of processes reqmres at least 2 + values A technical restncnon on [he model increases this reqmrement to N/2 values, whde achieving a fixed bound on wamng further increases the reqmrement to N + 1 values. These bounds are shown to be nearly optimal, for algorithms are exhibtted for the last two cases which use [NJ2] + 9 and N + 3 values, respectively All of the lower bounds apply a fortJori to the space requirements for weaker pnmitves, such as P and V, using busy wamng Categories and Subject Descriptors D 4 1 ]Operating Systems]' Proces Managemen;--mutual excluswn; D 4 2 IOperatlng Systems]' Storage Management F I I [Computatloa by Abstract Device9]: Models of Computanon, F 1.2 [Computation by Abstract Devices]' Modes ofComputatton--?arallehsm, F 2 [lheory of Computation] Analysis o Algomhms and Problem Complexity General Terms Algorithms, Performance, Theory Addmonal Key Words and Phrases' critical section, test and set, asynchronous processes. synchTomzauo l.

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