in reply to Re: while loop acting up, though I'm not sure how
in thread while loop acting up, though I'm not sure how

That adds information, but I still don't see the bug. The output is

Use of uninitialized value $previoustime in subtraction (-) at soonix.
+pl line 15.
1447773471 at MWE.pl line 22.
before sleeping: time = 1447773471, $time = 1447773471,
after sleeping:  time = 1447773481, $time = 1447773471,
1447773471 at MWE.pl line 22.
1447773481 at MWE.pl line 22.
before sleeping: time = 1447773481, $time = 1447773481,
after sleeping:  time = 1447773491, $time = 1447773481,
1447773481 at MWE.pl line 22.
1447773491 at MWE.pl line 22.
before sleeping: time = 1447773491, $time = 1447773491,
after sleeping:  time = 1447773501, $time = 1447773491,
1447773491 at MWE.pl line 22.
1447773501 at MWE.pl line 22.

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etc. The reason for the second warn each time around is (presumably) because mysleep doesn't get called i.e. because !($time - $previoustime >= 10) i.e. (presumably) because $time - 10 < $previoustime. But that's not the case: after all, we've set $previoustime = $time (which we were just warned is time - 10) and then $time = time. So I still don't get what's going on.

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Re^3: while loop acting up, though I'm not sure how
by soonix (Chancellor) on Nov 17, 2015 at 20:40 UTC
    • The first time, $previoustime is undefined (warning from "line 15"), hence ($time - $previoustime >= 10) is true and the rest of the or is ignored (first "line 22" warning), because the loop condition is true anyway.
    • Second time the condition is evaluated: Since in the previous iteration the condition was true without sleep, the time assignment happened within the same second as the previous one, resulting in a sleep 10
    • Third time: After the sleep, time has advanced by 10 seconds, ($time - $previoustime >= 10) being true again, same situation as in first iteration, i.e. no sleep.
    • Fourth iteration is just like the second
    The sleep is not evaluated (hence, not executed) every odd iteration because of the "short-circuit" nature of perl's boolean operators. davido explains this thoroughly in Perl Idioms Explained - && and || "Short Circuit" operators - despite the subject, this is also regarding and and or.
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      Thank you.
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