Thank you very much. I refined my code like below. I put waitpid in the "for" loop, but move print and rename out of the "for" loop, then everything is ok. Is it the right behavior? 
    close($fh);
    close($logfile);
    exit; # exit child process
  } 
  waitpid($pid,0); 
}

print "Parent Process";
close($fh); # Close file handler $fh
close($logfile); # Close file handler $logfile    
rename ($filename, $newfilename) or die "Error in renaming $!"; # Rena
+me the temporary to avoid node exporter seeing half a file.
alarm(0);

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In reply to Re^4: Multiprocess - child process cannot be finished successfully by wonderG
in thread Multiprocess - child process cannot be finished successfully by wonderG

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