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Full Discussion: How many semaphores?
Top Forums UNIX for Advanced & Expert Users How many semaphores? Post 302144201 by Watto86 on Tuesday 6th of November 2007 04:05:05 PM
Old 11-06-2007
How many semaphores?

Hello, first of all I apologize if this thread is not in the correct section of this forum, but this one just seemed the most appropriate.
The question I have does not concern Unix specifically, it applies to virtually any OS, however it is in Unix where I learned about this problem.

So, the question is: What is the least number of semaphores needed to guarantee that n processes will run in a specified order ("chain of processes"), like this:

P1 -> P2 -> P3 -> ...... -> Pn ?

It means that P2 will not be allowed into critical section before P1 has exited it, P3 will not go before P2, and so on.

I would really appreciate if you could comment on this, since I am trying to get the correct answer for quite some time and nobody I asked could provide the answer.
Thank you.
 

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ARITHMETIC(6)							   Games Manual 						     ARITHMETIC(6)

NAME
arithmetic - provide drill in number facts SYNOPSIS
/usr/games/arithmetic [ +-x/ ] [ range ] DESCRIPTION
Arithmetic types out simple arithmetic problems, and waits for an answer to be typed in. If the answer is correct, it types back "Right!", and a new problem. If the answer is wrong, it replies "What?", and waits for another answer. After every twenty problems, it publishes statistics on correctness and the time required to answer. To quit the program, type an interrupt (delete). The first optional argument determines the kind of problem to be generated; +-x/ respectively cause addition, subtraction, multiplication, and division problems to be generated. One or more characters can be given; if more than one is given, the different types of problems will be mixed in random order; default is +-. Range is a decimal number; all addends, subtrahends, differences, multiplicands, divisors, and quotients will be less than or equal to the value of range. Default range is 10. At the start, all numbers less than or equal to range are equally likely to appear. If the respondent makes a mistake, the numbers in the problem which was missed become more likely to reappear. As a matter of educational philosophy, the program will not give correct answers, since the learner should, in principle, be able to calcu- late them. Thus the program is intended to provide drill for someone just past the first learning stage, not to teach number facts de novo. For almost all users, the relevant statistic should be time per problem, not percent correct. 7th Edition May 6, 1986 ARITHMETIC(6)
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