SQLite 3, php, locking table

lets imagine two scripts: one what is getting datas from a table, and another what writes it. While A is running, during the process it must always get the same results, if the B writes to the table, A might goes wrong.

A:

session_start(); session_write_close();

set_time_limit(0);
$file_db = new PDO('sqlite:'.dirname(__FILE__).'/table.sqlite3');
$file_db->setAttribute (PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$file_db->exec('DROP TABLE IF EXISTS messages');
$file_db->exec('CREATE TABLE IF NOT EXISTS messages (id INTEGER PRIMARY KEY AUTOINCREMENT, title TEXT)');
$file_db->query('INSERT INTO messages VALUES (1, "'.rand(1,99999).'")');
$file_db->setAttribute(PDO::ATTR_TIMEOUT, 9999999);
$m = date('U');
do
{
    $row = $file_db->query('SELECT title FROM messages WHERE ID = 1')->fetch();
    if ($row === false)
    {
        echo 'DELETED!<br>';
    }
    else
    {
        echo $row['title'].'; ';
        if (rand(1,5) == 1) { echo '<br>'; }
    }
    if (abs(date('U') - $m) > 10) { break; }
} while(true);
echo '<hr>';
$file_db->setAttribute(PDO::ATTR_TIMEOUT, 0);
foreach ($file_db->query('SELECT title FROM messages WHERE ID = 1') as $row)
{
    var_dump ($row); echo '<br>';
}

B:

session_start(); session_write_close();

$i = 0;
set_time_limit(0);
$file_db = new PDO('sqlite:'.dirname(__FILE__).'/table.sqlite3');
$file_db->setAttribute (PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$m = date('U');
do
{
    switch (rand(1,2))
    {
        case 1 :
            $file_db->query('DELETE FROM messages');
            break;
        case 2 :
            $file_db->query ('UPDATE messages SET title = 0');
            break;
    }
    if (abs(date('U') - $m) > 1) { break; }
} while(true);

so A is running for 10 seconds, B for 2 seconds, and if you run B while A is running, A echoes zero, or no result. Thats normally normal, but I want to lock that table, how to do that? And what happens if B tries to modify it then, an exception? Cant B just hold until table gets unlocked? I read that PDO::ATTR_TIMEOUT is for it, but it has no effect