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Editorial Team
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Asked: 2026-06-03T13:21:42+00:00

It’s a web server scenario. Linux is the OS. Different IP Addresses call the

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It’s a web server scenario. Linux is the OS. Different IP Addresses call the same script.

Does Linux start a new process of Perl for every script call or does Perl run the multiple calls interleaved or do the scripts run serially (one after another)?

Sorry, I didn’t find an answer within the first few results of Google.

I need to know in order to know how much I have to worry about concurrent database access.

The script itself is NOT using multiple threads, it’s a straightforward Perl script.

Update: more sophisticated scheduler or serialiser of comment to answer below, still untested:

#! usr/bin/perl

use Fcntl;
use Time::HiRes;


sysopen(INDICATOR, "indicator", O_RDWR | O_APPEND); # filename hardcoded, must exist
flock(INDICATOR, LOCK_EX);
print INDICATOR $$."\n";    # print a value unique to this script
                            # in single-process context it's serial anyway
                            # in multi-process context the pid is unique
seek(INDICATOR,0,0);
my $firstline = <INDICATOR>;
close(INDICATOR);

while("$firstline" ne $$."\n")
{
    nanosleep(1000000);     # time your script to find a better value
    open(INDICATOR, "<", "indicator");
    $firstline = <INDICATOR>;
    close(INDICATOR);
}

do "transferHandler.pl";    # name of your script to run

sysopen(INDICATOR, "indicator", O_RDWR);
flock(INDICATOR, LOCK_EX);
my @content = <INDICATOR>;
shift @content;
truncate(INDICATOR,0);
seek(INDICATOR,0,0);
foreach $line(@content)
{
    print INDICATOR $line;
}
close(INDICATOR);

Edit again: above script would not work if perl runs in a single process and threads (interleaves) scripts itself. Such a scenario is the only one of the 3 asked by me which appears not to be the case based on the answer and feedback I got verbally separately. Above script can be made to work then by changing the unique value to a random number rather than the pid on quick thought however.

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1 Answer

  1. Editorial Team

    It is completely depended on set up of your web server. Does it uses plain CGI, FastCGI, mod_perl? You can set up both of scenarios you’ve described. In case of FastCGI you can also set up for a script to never exit, but do all its work inside a loop that keeps accepting connections from frontend web server.

    Regarding an update to your question, I suggest you to start worrying about concurrent access from very start. Unless you’re doing some absolutely personal application and deliberately set up your server to strictly run one copy of your script, pretty much any other site will sometime grow into something that will require 2 or more parallel processing scripts. You will save yourself a lot of headache if you plan this very common task ahead. Even if you only have one serving script, you will need indexing/clean up/whatever done by offline tasks and this will mean concurrent access once again.

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