in reply to Re^2: Spinning cursor while waiting for search/copy process to be finished
in thread Spinning cursor while waiting for search/copy process to be finished

You may have thought that the spin subroutine somehow runs at the same time with the main process, but that's not true: it's called in each iteration of the loop, $j never exceeds 1 (as explained), so each turn of the loop waits for 0.1*4=0.4 seconds and prints four characters: -, \, |, and /. You may want to use threads to make your subroutine run in parallel, as suggested above.

The idea of the spin function is printing only one character each time, incrementing the counter and continuing the loop, without sleeping or waiting for something else, without any inner loops. Consider this code: 

sub spin {
 # as "golfy" as I could imagine for now
 print [qw{/ - \ |}]->[$_[0]++]."\033[1D";
 $_[0]%=4;
}
# ...
#somewhere outside the loop
my $j = 0;
# ...
foreach (@list_level_current_version) {
 spin($j); # print next spinning character
 # do the useful work
 if ($_ =~ /\Q$pattern/) { $dir = $_; last OUTER; } 
 # ...
}

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The spin subroutine constructs an array of spinning characters, prints the character passed to it by index as the first argument, increments the index by one and makes it the remainder of devision by 4 (so it doesn't exceed possible index of spin character array). By modifying $_[0] directly it automatically modifies the $j variable passed as argument.

Edit: little rephrasing in the first paragraph
Sorry if my advice was wrong.

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Re^4: Spinning cursor while waiting for search/copy process to be finished
by Ingvar (Novice) on Mar 25, 2013 at 07:28 UTC

    Thanks a lot, it works perfectly well! The only thing I am still missing is how it can work? I mean, what is the function of $j variable if it is always 0? how is spin($j) processed then?

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      spin($j) increments $j by editing its $_[0]. As perlvar says,
      A function is free to do in-place modifications of @_ and change its caller's values. 
      upcase_in($v1, $v2);  # this changes $v1 and $v2
sub upcase_in {
 for (@_) { tr/a-z/A-Z/ }
}

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      Scalars are already passed by reference, so you can modify scalar arguments without using typeglob mechanism (skipped) by referring explicitly to $_[0] etc.
      Sorry if my advice was wrong.
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        Thanks a lot!

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        Sorry, there is one more thing: suppose, the process is just in one statement, not a loop:

        copy ("$source", "$destination");

        It does take long because the source is a big file on a network resource. I tried it this way:

        while (my $result = copy ("$source", "$destination")) {
spin($j);
}

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        But I don't quite like what is going on: it spins, then makes a long pause, then spings again... Is there any trick I could use to make them work as if in parallel?

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