I am not using any synchronzation( no queues, no semaphores). And the second thread is spawned after the file is downloaded completely to the web server.

In the main while loop, i do the following

      foreach (@connections_pending) {
            my $fh;
            my $remote = accept( $fh, $_ );
            my ( $port, $iaddr ) = sockaddr_in($remote);
            my $peeraddress = inet_ntoa($iaddr);
            my $t = threads->create( \&connection, $fh );
      }
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So when the request for file upload comes from front0end, i spawn the thread.

Now, in the connection subroutine, i check if its a POST method and if so, i call a subroutine to handle that

sub upload_file {    
        my ( $fh, $req_ ) = @_;
    my %req     = %$req_;
    my $header_ = $req{HEADER};
    my %header  = %$header_;

        my ($file, $desc, $dirpath ) = (undef, undef, undef);
    my $boundary = trim (form_data_boundary( $header{'content-type'} )
+);
    my $user_agent = $header{'user-agent'};

 # Now i will process the post buffer and copy the file #to local mach
+ine into a temp directory. I shall also #receive the filename, destin
+ation directory and some #other metadata information.

($file, $desc, $dirpath) = process_POST_buffer($fh, $req_, $boundary);

# Then i spawn another thread to do the pre-processing on this file
my $t = threads->create( \&pre_process, $file, $desc, $dirpath );

}
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The pre-process thread does this

sub pre_process {
    threads->detach();
    my ( $file_name, $desc,  $dirpath ) = @_;
    my ( $file1,  $file2, $file3 )   = ( getTempFile(), getTempFile(),
+ getTempFile() );
    my $metadata = i_PreProcessor->new(
        FILENAME      => $file_name,
        SEARCHXMLFILE => $file1,
        DESCRIPTION   => $desc,
        MAPXMLFILE    => $file2,
        TAGXMLFILE    => $file3,
        DIRNAME       => $dirpath
    );
    $metadata->build2();

    #delete temp files.
    my @files = ( $file1, $file2, $file3 );
    unlink(@files);
    threads->exit();
}
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