A clock is reading 10:27:54.0. (hr:min:sec) when it is discovered to be 4 seconds fast. Explain why
it is undesirable to set it back to the right time at that point and show (numerically) how it should
be adjusted so as to be correct after 8 seconds has elapsed.
What will be an ideal response?
Some applications use the current clock value to stamp events, on the assumption that clocks always advance.
We use E to refer to the ‘errant’ clock that reads 10:27:54.0. when the real time is 10:27:50. We assume that H
advances at a perfect rate, to a first approximation, over the next 8 seconds. We adjust our software clock S to
tick at rate chosen so that it will be correct after 8 seconds, as follows:
S = c(E - Tskew) + Tskew, where Tskew = 10:27:54 and c is to be found.
But S = Tskew+4 (the correct time) when E = Tskew+8, so:
Tskew+ 4 = c(Tskew + 8 - Tskew) + Tskew, and c is 0.5. Finally:
S = 0.5(E - Tskew) + Tskew (when Tskew ð E ð Tskew+8).
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Indicate whether the statement is true or false
The vast majority of computer systems in use today do allow at least some kinds of deadlock and indefinite postponement situations to develop, and many of these systems provide no automatic means of detecting and recovering from these problems. In fact, many designers believe that it is virtually impossible to certify a system as absolutely free of the possibilities of deadlock and indefinite postponement. Indicate how these observations should affect the design of “mission-critical” systems.
What will be an ideal response?