XML CO631 Anonymous Questions and Answers Keyword Index

This page provides a keyword index to questions and answers. Clicking on a keyword will take you to a page containing all questions and answers for that keyword, grouped by year.

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Keyword reference for timers

Question 110 (2004):

Is this the correct piece of code for waiting a random time ?

    SEQ          
      seed := seed + id
      i, seed := random(num, seed)
      tim ? t
      tim ? AFTER t PLUS i

Answer 110:

More or less, yes. Make sure you initialise "seed" appropriately though -- the code above initialises it based on itself (if undefined, it'll stay undefined). As covered in the seminars, a quick way to get an initial seed value is:

    tim ? seed
    seed := (seed >> 2) + 1   -- maybe also add in the `id'

Remember also that your seed should be explicitly initialised like this just once -- before loop entry. Within the loop, cycling through the philosopher's life, the seed value gets updated as you use the random function. The sequence of seed values takes you through the "random" numbers. If you re-initialise the seed every time round the loop, the computed randomness will be lost.

Keywords: q7 , timers

Question 59 (2004):

Hi, what is the best way to to wait 1 second within a loop ? (Required for q5)

Answer 59:

See the answer to Question 80 (2000).

Keywords: timers

Question 37 (2002):

Could you please explain a little more how you would go about implementing the random time delay? I have read through the previous questions on it but I'm still a little lost. Is the time delay between philosophers doing different actions or in the display process?

Answer 37:

It's in the philosopher processes - not the display.

The question says:

Thinking and eating by the philosophers should be modelled by random (but finite!) delays

In the "philosopher" process there are two folds:

  <!--{{{  think-->
  SKIP
  <!--}}}-->

and:

  <!--{{{  eat-->
  SKIP
  <!--}}}-->

You should replace the SKIPs by random delays.

Keywords: q7 , random , timers

Question 80 (2000):

Thinking and eating by the philosphers should be modelled by random (but finite!) delays.

Assuming we have obtained a random number, what's the best way to implement the delay ... i.e. pause execution for a random time? Is there a wait(time) function or such like?

Answer 80:

See slide 4-40 and sections 3.4/3.5 of the "OCCAM2 CHECKLIST" paper. Spelling it out:

  TIMER tim:
  INT t:
  SEQ
    tim ? t
    tim ? AFTER t PLUS waiting.time

Keywords: q7 , timers

Referrers: Question 59 (2004)

Question 79 (2000):

When it comes to TIMERs, how is the time counted? Does the internal enviornment time in nanoseconds or microseconds? Also does it go like this:

  1000000 nanoseconds = 1 second
  10000 microseconds = 1 second

Answer 79:

occam TIMERs, in KRoC Solaris/Linux systems, increment every microsecond. And, for information:

  1000000000 nanoseconds = 1 second
  1000000 microseconds = 1 second

Keywords: timers