This is probably the reason why many of us say "don't use threads for this task".

Even though you admit to having made little (no?) use of threads?

If you encountered a bug in a regex, that allowed the regex to work but causes a warning during global destruction, would you advocate the replacement of all regexes using character by character comparisons and huge if/else cascades?

Eg. You'd advocate if( $string =~ m[C\d\[A-Q]] ) { with

my $currentChar = substr( $string, $n, 1 );
if( $currentChar eq 'C' ) {
    $currentChar = substr( $string, ++$n, 1 );
    if( $currentChar eq '1' ) {
        $currentChar = substr( $string, ++$n, 1 );
        if( $currentChar eq 'A' ) {
        ...
        ...
        ...
        ...

        elsif( $currentChar eq 'B'
        ...
        ...
        ...
        ...
    }
    elsif( $currentChar eq '2' ) {
        ...
        ...
        ...
        ...
    }
    elsif( $currentChar eq '3' ) {
        ...
        ...
        ...
        ...
    }
    elsif( $currentChar eq '4' ) {
        ...
        ...
        ...
        ...
    }
    elsif( $currentChar eq '5' ) {
        ...
        ...
        ...
        ...
    }
    elsif( $currentChar eq '6' ) {
        ...
        ...
        ...
        ...
    }
    elsif( $currentChar eq '7' ) {
        ...
        ...
        ...
        ...
    }
    elsif( $currentChar eq '8' ) {
        ...
        ...
        ...
        ...
    }
    elsif( $currentChar eq '9' ) {
        ...
        ...
        ...
        ...
    }
    else {
        die "The second char was not in range '1' thru '9';
    }
}
else {
   die "The first character didn't match 'C'";    
}
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Because that is the logical equivalent of your advice!

Or might you suggest working around the problem, and report the error, in the hope that the regex engine would get fixed?