Thank you very much. I want to rename the name of $filename after all child process finished writing. Each child process will write to $filename cumulatively. The purpose of the script is to test network connection for every host. In the "for" loop, itis to create child processes to test the connection concurrencily, and meanwhile write to $filename. The alarm is for network connection timeout, if after 60s, the connection is still unable to setup, then will go to $SIG{ALRM} to print error message. 
use strict;
use Fcntl qw(:DEFAULT :flock);
use FindBin qw($Bin);
use lib "$Bin";
use JSON;
use POSIX;


my $JSON_FILE = $ARGV[0];

open my $file, '<', $JSON_FILE or die("$JSON_FILE Could not open file:
+ $!\n");

my $data;
eval {
  $data = decode_json(<$file>);
  print $data;
};
if ( $@ ){
  print "Json file parsing failed.\n";
} 

my $targets = $data;

my $filename = "/var/log/a.tmp"; 
my $newfilename = "/var/log/a.log";
open (my $fh, ">", $filename) or die "Could not open file '$filename' 
+$!\n";

my $time = strftime('%d-%m-%Y %H:%M:%S',localtime);

for (my $index=0; $index <= $#$targets; $index++){    
  my $array = $targets->[$index]{label};
  my $hostaddress = $array->{ip};
  
  $time = strftime('%d-%m-%Y %H:%M:%S',localtime);
     
  defined(my $pid = fork) or die "fork failed: $!";
  unless( defined($pid) ) {
    flock $fh, LOCK_EX;
    print $fh "Can't execute check: can't fork(): $!\n";
    flock $fh, LOCK_UN;
  }

  unless($pid) { # child
    print "child: $$\n";
    my $var;
    eval {
      $var = #setup a network connection...;
      $SIG{ALRM} = sub { flock $fh, LOCK_EX;
                     print $fh "\n"; 
                     flock $fh, LOCK_UN;};
      alarm(60);
    };
    if( $@ ) {
      flock $fh, LOCK_EX;
      print $fh "Connection failed $@\n"; 
      flock $fh, LOCK_UN;
    }
    unless( $var ) {
      flock $fh, LOCK_EX;
      print $fh "Connection failed";
      flock $fh, LOCK_UN;
    }
    else {
      flock $fh, LOCK_EX;
      print $fh "Connection failed\n";
      flock $fh, LOCK_UN;
    } 
    close($fh);
    exit; # exit child process
  } 
  waitpid($pid,0); 
}

print "Parent Process";
close($fh); # Close file handler $fh 
rename ($filename, $newfilename) or die "Error in renaming $!";
alarm(0);

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In reply to Re^6: Multiprocess - child process cannot be finished successfully by wonderG
in thread Multiprocess - child process cannot be finished successfully by wonderG

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