Generating same seed between 2 processes

alih110 has asked for the wisdom of the Perl Monks concerning the following question:

Hello, I have 2 perl processes which are running one after the other through a Makefile. During each run I would like to see both the perl processes get the same seed. A unique seed needs to be generated in each run. Both the perl processes are the same perl file run in 2 threads but sequentially. For example: This is what I would like: Run 1 : Perl process 0 generates seed 1446 and Perl process 1 also generates the same seed Run 2 : Perl process 0 generates seed 1245 and Perl process 1 also generates the same seed and so on..... I tried using time() function in my perl program but each perl process got a different seed with that. Any ideas how I can get both of them to get the same seed?

Comment on Generating same seed between 2 processes

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Re: Generating same seed between 2 processes by ikegami (Patriarch) on May 15, 2008 at 04:51 UTC
You'd need to pass the same seed to `srand` in both processes. You could generate the seed in the parent and pass it to the Perl scripts via the environment or an argument. `$ set seed=$RANDOM # Or whatever $ perl -e'$,=" "; $\="\n"; srand($ARGV[0]); print rand, rand, rand;' $ +seed 0.17082803610629 0.749901980484964 0.0963716556235674 $ perl -e'$,=" "; $\="\n"; srand($ARGV[0]); print rand, rand, rand;' $ +seed 0.17082803610629 0.749901980484964 0.0963716556235674` [download]	[reply] [d/l] [select]
Re: Generating same seed between 2 processes by BrowserUk (Patriarch) on May 15, 2008 at 04:52 UTC
Add a third process that generates your random seed, and then supplies it to the two existing processes via their command lines: `perl -e"$s= rand; qx[$argv[0] $s]; qx[ $ARGV[1] $s];" script1.pl scrip +t2.pl` [download] Switch command line conventions as appropriate. Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply] [d/l]
Re: Generating same seed between 2 processes by moritz (Cardinal) on May 15, 2008 at 07:49 UTC
Are you trying to crack Debian's ssh keys? ;-)	[reply]
Re: Generating same seed between 2 processes by toolic (Bishop) on May 15, 2008 at 13:30 UTC
Same thing, but using an environment variable. Here is the Makefile: `> cat Makefile SEED := ${shell perl -e 'print int rand 10_000'} .EXPORT_ALL_VARIABLES: .PHONY: all all: @perl proc0 @perl proc1` [download] Here is the 1st script: `> cat proc0 use warnings; use strict; if (exists $ENV{SEED}) { srand $ENV{SEED}; } else { die "Error: need a seed.\n"; } print "$0 ", rand, "\n";` [download] Here is the 2nd script: `> cat proc1 use warnings; use strict; if (exists $ENV{SEED}) { srand $ENV{SEED}; } else { die "Error: need a seed.\n"; } print "$0 ", rand, "\n";` [download] Now run it a few times: `> make proc0 0.0394185183840854 proc1 0.0394185183840854 > make proc0 0.821407354044826 proc1 0.821407354044826 > make proc0 0.697487873098911 proc1 0.697487873098911` [download]	[reply] [d/l] [select]