Prevent duplicate posts in wp_insert_post using custom fields

To save the link in the post meta you can use update_post_meta

like this for example:

$url = "http://sample.com/entertainment/default.aspx?tabid=2305&conid=102950"
$my_post = array(
    'post_title' => "$title",
    'post_content' => "$content",
    'post_status' => 'draft',
    'post_author' => 1,
    'post_category' => array(1),
);

$post_id =  wp_insert_post( $my_post );
update_post_meta($post_id,'source_link',$url);

and to prevent the insertion add a simple conditional check:

$args = array("meta_key" => "source_link", "meta_value" =>$url);
$posts = get_posts($args);
if (count($posts) < 0){
    //add new post
}

if (count($posts) < 0){
    //add new post
}

is not working, change it to

if (empty($posts)){ 
    //add new post
}