Boots – shoes – and leggings
Patent
1977-10-11
1980-02-19
Nusbaum, Mark E.
Boots, shoes, and leggings
364200, G06F 918
Patent
active
041897714
ABSTRACT:
The wait relations among N tasks in a multiprocessing, multiprogramming CPU environment are conformed to a vector of N+1 fields recording which tasks in a system are active and upon what other task any given task directly waits. The vector may be stored in a global register. Positions 1 through N are assigned to the N tasks such that a value p in position r means that task r is waiting directly on task p. One value j of the possible values 0,1,2, . . . , N+1 is designated to indicate an active task. Position j always shows the value j. Without loss of generality and to facilitate the discussion j is assumed to be 0. Thus, the value 0 in register position r means that task r is not waiting and position 0 always has the value 0.
The presence of any deadlocks (closures) among the wait relations can always be detected by the computing system by making repeated translations of the vector fields within and upon themselves in no more than log.sub.2 (N+1) iterations. In this regard, log.sub.2 (N+1) denotes the smallest integer equal to or greater than the base 2 logarithm. The translation of fields within and upon themselves means that for each global register position r containing pointer p, then the contents g of register position p are substituted as the new contents of position r for the iteration 0.ltoreq.r, p, g.ltoreq.N.
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Lum, "Deadlock Detection and Breaking", IBM T.D.B. vol. 13, No. 12, May 1971, pp. 3799, 3800.
Collier, "Algorithm for Detection of System Deadlocks", IBM T.D.B., vol. 12, No. 2, 7/1969, pp. 357-359.
Olbermarck, "Deadlock Detecting Enqueue-Dequeue", IBM T.D.B. vol. 13, No. 12, 1/71, pp. 2338, 2339.
Witt, "The Functional Structure of OS/360-Joband Task Management", IBM Systems Journal, vol. 5, No. 1, 1966, pp. 12-29.
Brodie R. Bruce
International Business Machines - Corporation
Nusbaum Mark E.
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