On 17.05.2016 20:26, demerphq wrote:
On 17 May 2016 at 20:23, demerphq <demer...@gmail.com> wrote:
On 16 May 2016 at 20:03, Bruce Johnson <john...@pharmacy.arizona.edu> wrote:
On May 16, 2016, at 10:15 AM, André Warnier (tomcat) <a...@ice-sa.com> wrote:
join "", map +(0..9,"a".."z","A".."Z")[rand(10+26*2)], 1..32 ;
looks at first sight to me like quite inefficient and probably likely to
generate the same string regularly, even if it does not look that way.
(The only variable there is rand(), and it can only return values between 0 and
62).
The function is meant to map a random element from the 62-element-long array
(0..9,"a".."z","A".."Z”) (hence a rand() call to generate a number from 0 and
62), 32 times, and join them into a string.
Although I think that should really be rand(9+26*2) to properly generate array
indices for the entire array and no more. With a number between 0 and 62 (63
numbers) and a 62-element array, you’ll be retrieving nulls from the array 1/62
calls, but all that means is that the string is one char shorter for each time
'62’ comes up...
So long as rand is properly seeded, you should not get repeats, at least not
frequently enough to ever notice, I’d think.
This is textbook Perl, as in I’m pretty sure it’s out of one of Larry Wall’s
books; I use it to generate random strings for cookies.
If it’s properly seeded in the original code, it should either work or not work
on all five servers. Not working on one out of the five makes me think maybe
there’s some sort of weird caching issue.
Or for some reason one of the servers goes through a code path where
it calls srand/rand prefork.
An unfortunate side effect of the rules of srand in perl is that if
you fork without calling rand each child process will have their own
seed. if you rand before fork then all the children will have their
own seed.
Sorry, that should read "if you rand before fork then all the children
will SHARE THE SAME SEED".
I personally consider this a bug in Perl, but I doubt it will get fixed.
I think that the children will share the same seed in any case. (That sounds kind of
biblical..).
The point is, all children have initially a copy of the same pristine perl interpreter,
and the initial grand-father seed (to the initial srand()) is in there somewhere.
Only if each child starts by an srand($my-own-unique-seed), will they subsequently get a
different sequence of rand() responses.
