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Re^3: coming out of perl script after 10 min.

by BrowserUk (Pope)
on Mar 06, 2013 at 19:30 UTC ( #1022071=note: print w/ replies, xml ) Need Help??


in reply to Re^2: coming out of perl script after 10 min.
in thread coming out of perl script after 10 min.

  1. alarm works without active waiting,

    Since the advent of SAFE_SIGNALS; alarm won't interrupt long running opcodes.

    And the cpu requirement of the "active waiting" -- waking 1 per second:

    C:\test>perl -E"sleep 1 for 1..120; say join ' ', times" 0 0.015 0 0

    0.015/120 = 0.0125% cpu usage; means that it would require 8000 of these actively waiting tasks to even register a blip on a cpu usage graph.

  2. sleep 1 does not always sleep exactly one second.

    On modern OSs, the differences are tiny -- essentially the time taken between the 1 second elapsing and the process getting its next time-slice:

    C:\test>perl -MTime::HiRes=time -E"$t=time; sleep 1 for 1 .. 10*60; pr +int (time()-$t) - 10*60" 601.386687040329

    601.386687040329 - 600 / 600 = 0.002311145067215. A couple of milliseconds

    Which means that after 10 minutes of waiting, those tiny differences will have accumulated such that you've ended up giving the user a whole extra second in which to respond. Big deal.

    But the kicker is: alarm will suffer from the essentially the same delays and inaccuracies! Once the system timer times out and sets the flag in the kernel thread structure; it still won't run until it filters its way to the top of the schedulers list of run-eligible threads.

Re-reading the post to which you responded and the OP; the former is almost certainly not a solution to the latter -- but definitely not because of the reasons you cite. They are just sweating the small stuff whilst ignoring the bigger picture.


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