lock doesn't work the way you seem to think it does. Only few operating systems have mandatory file locking, and locking only works between processes, not within a single process.

If you want to prevent other parts of your program from printing output to the screen, you will have to reopen STDOUT to something else:

my $old_STDOUT = \*STDOUT;
my $capture;
open STDOUT, '>', \$capture
    or die "Couldn't do in-memory capture of program output: $!";
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If you have subprocesses that output to the screen, you will have to redirect or capture their output (via shell pipes or IPC::Open or IPC::Open3).

so you suggest filtering all things 
through a shell pipe...im not sure how
i could use that to have lock-similar functionality.
im into multithreading not multiprocesses.
im thinking of making a separate

my $buffer:shared="";
sub PRINT {
 lock $buffer;
 $buffer.=shift;
}

sub dump_on_screen {
 lock $buffer;
 print $buffer;
 $|++;
 $buffer="";
}
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and have a thread say...PRINT_THREAD that
periodically prints stuff to the screen
but in the order they happened in real-time
my $pt=threads->new(\&PRINT_THREAD);
sub PRINT_THREAD {
 dump_on_screen();
}
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i havent been clear enough in what i want to do
actually, i have a multithreding app and i want
to print stuff on the screen just as they happen.
i want print to be atomic so thats why i want to
lock the screen before i start doing anything.
id like to get the order in wich threads 

i havent been clear enough in what i want to do actually, i have a multithreding app and i want to print stuff on the screen just as they happen. i want print to be atomic so thats why i want to lock the screen before i start doing anything. id like to get the order in wich threads

In that case, I don't think you want to lock the screen but set STDOUT to be non-buffering. See the $| entry in perlvar or Suffering from Buffering.

-derby

Update: At the beginning of your script, I would set STDOUT to be non-buffering:

 select STDOUT; $| = 1;
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