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Re^3: forks for running multiple codes at same time

by weismat (Friar)
on Feb 09, 2009 at 07:54 UTC ( #742367=note: print w/ replies, xml ) Need Help??


in reply to Re^2: forks for running multiple codes at same time
in thread forks for running multiple codes at same time

I agree that there is no difference if you would create as many threads as forked processes.
The difference is that you need to call fork once for every planned task - whereas in a thread model you can share data and thus you would start threads only 5 times depending on the number of workers as the workers can get the data from a queue instead of a function parameter.


Comment on Re^3: forks for running multiple codes at same time
Re^4: forks for running multiple codes at same time
by salva (Abbot) on Feb 09, 2009 at 09:32 UTC
    In the OP case, where the final intend is to run an external command, the optimum solution would probably be to fork a new process and exec the command.

      forking, and then calling system to run the command, means he's forking twice for every command. Maybe 3 times depending what's in $command.

      You can achieve the goal without threads on win32 like this:

      #! perl -slw use strict; my @dates = 1 .. 10; my @pids; (my $cmd = <<'CMD' ) =~ s[\s+][ ]g; -wle"print qq[task $ARGV[0] starting]; sleep rand( 10 ); print qq[task $ARGV[ 0 ] finishing];" CMD while( my $date = pop @dates ) { push @pids, system 1, 'perl.exe', "$cmd $date"; if( @pids >= 5 ) { my $kid = wait; @pids = grep $_ != $kid, @pids; } } waitpid $_, 0 for @pids;

      Since you need to load a new executable, why not just start it in a new process rather than duplicating the current one first?


      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.
        Since you need to load a new executable, why not just start it in a new process rather than duplicating the current one first?

        Well, I was thinking about Unix systems where calling fork & exec is the standard (and sometimes only) way to start a new process. On Windows, you are right, it will be quite inefficient.

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