Hi monks, I am trying to writing log file in xml with XML::LibXML 1.5x after I do some processing, but something string occur: some element is missing in final xml:

    my $parser = XML::LibXML->new();
    my $doc = $parser->parse_file($file);
    $root = $doc->documentElement();
    $cdoc = $doc->getElementsById($docname);
    open(FH, ">", $file) or die "Open file '$tracefile' failed: $!\n";
    flock(FH, LOCK_SH);
    seek(FH, 0, SEEK_SET);
    
    for my $para ($document->getElementsByTagName ("p")){
        my $status = processing($para);
        
        my @paras = $root->getElementsByTagName('sentence');
        my $exist_para = $root->getElementsById($para->getAttribute("i
+d"));
        my $para_elem;
        if(!defined($exist_para)){
            $para_elem = $root->createElement('sentence');
            $para_elem->setAttribute('xml:id', $para->getAttribute("id
+"));
            $para_elem->setAttribute('index', scalar(@paras));
        }else{
            $para_elem = $exist_para;
        }
        if($status == 1){
            $para_elem->setAttribute('class', 'problem');
        }elsif($status == 0){
            $para_elem->setAttribute('class', 'fine');
        }else{
            $para_elem->setAttribute('class', 'skip');            
        }
        $cdoc->appendChild($para_elem);
    }
[download]

Result (partial):

<document src="0.xml" xml:id="0.xml" index="0">
<sentence xml:id="0_xml0002" index="0"/>
</document>
<document src="10.xml" xml:id="10.xml" index="1">

</document>
<document src="16.xml" xml:id="16.xml" index="3">
<sentence xml:id="16xml_0008" index="2"/>


</document>
[download]

The index here shown I get some trouble that the element is not written out while I am processing (seems instead of write out the element string, it print a newline only)....and they are really missing when I compare the log on the screen. It appear in both case that I write the file at once or parse/write repeatedly. Any Idea?