Perl generate random session id for high traffic - perl

Question

I am trying to generate a random id for sessions cookie for every user session in Perl. Of course I searched cpan and google and found many similar topics and same weakness. The most modules used are Digest::SHA and Data::UUID and the module Data::GUID which internally uses Data::UUID.
Here is the code I can summarize the most methods used in modules on cpan:
#!/usr/bin/perl
use v5.10;
use Digest::SHA;
use Data::UUID;
use Data::GUID;# uses Data::UUID internally, so no need for it
use Time::HiRes ();
for (1..10) {
#say generate_sha(1); # 1= 40 bytes, 256=64 bytes, 512=128 bytes, 512224, 512256
say generate_uuid();
#say generate_guid();
}
sub generate_sha {
my ($bits) = #_;
# SHA-1/224/256/384/512
return Digest::SHA -> new($bits) -> add($$, +{}, Time::HiRes::time(), rand(Time::HiRes::time()) ) -> hexdigest;
}
sub generate_uuid {
return Data::UUID->new->create_hex(); #create_str, create_b64
}
sub generate_guid {
# uses Data::UUID internally
return Data::GUID->guid;
}
Here is a sample output form Data::UUID module:
0x0217C34C6C0710149FE4C7FBB6FA663B
0x0218665F6C0710149FE4C7FBB6FA663B
0x0218781A6C0710149FE4C7FBB6FA663B
0x021889316C0710149FE4C7FBB6FA663B
0x021899E16C0710149FE4C7FBB6FA663B
0x0218AB2B6C0710149FE4C7FBB6FA663B
0x0218BB1D6C0710149FE4C7FBB6FA663B
0x0218CABD6C0710149FE4C7FBB6FA663B
0x0218DB786C0710149FE4C7FBB6FA663B
0x0218ED396C0710149FE4C7FBB6FA663B
The id's generated from these seems to be unique, but what I am concerning is about high traffic or concurrency, say what if a 1000 only not saying 1000,000 users connected at the same time either from the same process like running under FCGI (say each FCGI process serving only 10 users) or from separate processes like running under CGI mode.
In the SHA I used this random string:
($$, +{}, Time::HiRes::time(), rand(Time::HiRes::time())
it includes Anonymous hash reference address and the current time in microseconds with Time::HiRes::time. Is there any other ways to make random string.
I have read topics to add the Host name and IP address of the remote user but others say about proxies could be used.
I see Plack::Session::State module uses this simple code to generate id's:
Digest::SHA1::sha1_hex(rand() . $$ . {} . time)
So the question in short I want to generate a unique may be up to 64 bytes long session id guaranteed to work with high traffic.

Answer 1

You can safely use Data::UUID and you shouldn't be concerned about duplicates, you will not encounter them.
Also rand() will not return the same number when called subsequently even under assumption that it is called at the same moment of time. A pseudo random algorithm generates the next number based on its current state and the previously generated values. A true random generator is generally not used alone but in conjunction with a pseudo random number generator. In either case the likelihood of subsequently generated numbers to repeat between the nearest clock ticks in practical terms is negligible. In your example you may want to use rand(2**32).