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. Yves -- perl -Mre=debug -e "/just|another|perl|hacker/"
