Universität Bielefeld - Technische Fakultät |
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AG Rechnernetze und Verteilte
Systeme Arbeitsgruppe von Prof. Peter B. Ladkin, Ph.D. |
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From the Risk Forum 19.53 | |
Risks-19.53-9.2 Re: What really happened on Mars Rover Pathfinder (Mike Jones, R-19.49)From: Fred B. Schneider <
fbs@CS.Cornell.EDU> Readers of RISKS could get the wrong impression about who did what and when from what David Wilner is reported to have said in Mike Jones' item on the Mars Pathfinder mission in RISKS-19.49. This note attempts to provide some missing information. Jones' Mars Pathfinder article ends with: THE IMPORTANCE OF GOOD THEORY/ALGORITHMS David [Wilner] also said that some of the real heroes of the situation were some people from CMU who had published a paper he'd heard presented many years ago who first identified the priority inversion problem and proposed the solution. ... For the record, the paper was: L. Sha, R. Rajkumar, and J. P. Lehoczky. Priority Inheritance Protocols: An Approach to Real-Time Synchronization. In IEEE Transactions on Computers, vol. 39, pp. 1175-1185, Sep. 1990. Actually, a "priority inheritance" protocol can be found in
B. W. Lampson and D. D. Redell. which is a reprint of a paper that appeared in Dec 1979 (7th ACM Symposium on Operating System Principles). Below is the relevant excerpt; it is almost - but not exactly - what Sha et al. investigate.
So, it would be incorrect to credit Sha et al. for first *identifying* the problem or for first *proposing a protocol* to solve it. Lampson & Redell do not give any quantitative analysis of their prio scheme, though. The development of this thread of research in real-time scheduling is accurately described in section 5 of Audsley et al., as noted by Ken Tindell. A parable comes to mind. School children in the U.S. are taught that "Columbus discovered America". Ultimately they learn that Columbus was preceded by, among others, the Vikings. So why aren't they taught that "The vikings discovered America"? Perhaps it is because when Columbus discovered America, it stayed discovered. |
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Copyright © 1998 Peter B. Ladkin, 05. September 1998 | |
von Mirco Hilbert |