need help in understanding return values in fork().

[whn]

I worte a piece of perl code like this:

print "This is the original process #: $$\n";
my $ret = &watchProcess;
[COLOR=red][b]print "\$\$ = $$, \$ret = $ret\n";[/b][/color]

exit 0;

sub watchProcess {
  my $pid1 = fork();
  my $msg;
  if (not defined $pid1) {
    print "First Resources not avilable.\n";
  }
  elsif ($pid1 == 0) {
    print "This is the parent Process, \$\$ = $$, \$pid1 = $pid1\n";
    sleep 1;
    my $pid2 = fork();
    if (not defined $pid2) {
      print "Second Resources not avilable.\n";
    }
    elsif ($pid2 == 0) {
      print "This is the parent Process again, \$\$ = $$, \$pid1 = $pid1, \$pid2 = $pid2\n";
      #sleep 1;
      return "P2";
    }
    else { # 2nd child process
      print "This is 2nd Child Process. \$\$ = $$, \$pid1 = $pid1, \$pid2 = $pid2\n";
      waitpid($pid2, 0);
    }
    [b]return "P1";[/b]
  }
  else { # 1st child process
    print "This is 1st Child Process. \$\$ = $$, \$pid1 = $pid1\n";
    waitpid($pid1, 0);
    [COLOR=blue][b]sleep 1;[/b][/color] 
  }
}

Test run 1:

% [b]./tt.pl[/b]
This is the original process #: 24502
This is the parent Process, $$ = 24503, $pid1 = 0
This is 1st Child Process. $$ = 24502, $pid1 = 24503
This is the parent Process again, $$ = 24504, $pid1 = 0, $pid2 = 0
$$ = 24504, $ret = P2
This is 2nd Child Process. $$ = 24503, $pid1 = 0, $pid2 = 24504
$$ = 24503, $ret = P1
$$ = 24502, $ret = 1

Test run 2 (this time the sleep call in blue is commented out):

This is the original process #: 24699
This is the parent Process, $$ = 24700, $pid1 = 0
This is 1st Child Process. $$ = 24699, $pid1 = 24700
This is the parent Process again, $$ = 24701, $pid1 = 0, $pid2 = 0
$$ = 24701, $ret = P2
This is 2nd Child Process. $$ = 24700, $pid1 = 0, $pid2 = 24701
$$ = 24700, $ret = P1
$$ = 24699, $ret = 24700

Can someone explain to me why the 2nd return value is a ps number?

Thanks.

 

[travs69]

not an answer.. but have you ever tried parallel::forkmanager? I used it once and have never looked back.

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Travis - Those who say it cannot be done are usually interrupted by someone else doing it; Give the wrong symptoms, get the wrong solutions;