Php 会话\设置\保存\处理程序方法是否会丢失会话数据？

使用session\u set\u save\u处理程序时如何获取会话数据？ 刷新页面时，如果使用session\u set\u save\u处理程序，所有会话数据都会丢失。但是，如果我删除会话\u集\u保存\u处理程序，则一切正常！ 这是密码

<?php
/*
Session open (called by session_start( ))
Session close (called at page end)
Session read (called after session_start( ) )
Session write (called when session data is to be written)
Session destroy (called by session_destroy( ) )
Session garbage collect (called randomly)
*/
function sess_open($sess_path, $sess_name) {
    //print "Session opened.\n";
    //print "Sess_path: $sess_path\n";
    //print "Sess_name: $sess_name\n\n";
    return true;
}

function sess_close( ) {
    //print "Session closed.\n";
    return true;
}

function sess_read($sess_id) {
    //print "Session read.\n";
    //print "Sess_ID: $sess_id\n";
    return '';
}

function sess_write($sess_id, $data) {
    //print "Session value written.\n";
    //print "Sess_ID: $sess_id\n";
    //print "Data: $data\n\n";
    return true;
}

function sess_destroy($sess_id) {
    //print "Session destroy called.\n";
    return true;
}

function sess_gc($sess_maxlifetime) {
    //print "Session garbage collection called.\n";
    //print "Sess_maxlifetime: $sess_maxlifetime\n";
    return true;
}
session_set_save_handler('sess_open','sess_close','sess_read','sess_write','sess_destroy','sess_gc');
session_register_shutdown('session_write_close');
session_start();

if(isset($_SESSION['foo']))
$_SESSION['foo'] = "have the foo data";
else $_SESSION['foo'] = "no foo data";

echo  $_SESSION['foo'];
?>

它总是输出“拥有foo数据”。 谁能告诉我为什么？非常感谢

session_set_save_handler('sess_open','sess_close','sess_read','sess_write','sess_destroy','sess_gc');
session_register_shutdown('session_write_close');