Questions about how the new login user replaces the data of the original login user

New login users replace the original login user data information 1. when a user logs on, the user information is stored: $ _ SESSION ['logname'] = $ username; 2. query the user email storage directory based on user information: $ home = $ mysql-& gt; selectDirByName ($ username ); 3. replace the data of the original login user with the new login user
1. storing user information during user logon:
$ _ SESSION ['logname'] = $ username;

2. query the user mail storage directory based on user information:
$ Home = $ mysql-> selectDirByName ($ username );

3. read and send emails from the directory:
// Xml file name of the Mail Index (xml includes the Mail's from, title, to, date, bodyId, attachId)
$ Items = $ home ['home']. "/". $ index. ". items"; ($ index indicates the number of the inbox and the sender, such as 1 and 2)
// Parse the index
$ Audit = parse_xml_config ($ region, "mailindex ");

4. list emails based on the parsed email information.

This is the general process.
Problem: log on to two users in the same browser. the newly logged on user information will replace the logged on user information. I thought I replaced the mail storage directory in step 2, but I added unset ($ home) before. Which of the following problems may cause the problem? If the description is unclear, please advise.

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The same browser must be like this. when you log on to 2nd, the first one will become 2nd ....

This is amazing if you want to open two browsers.
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$ _ SESSION ['logname'] = $ username;
==>
$ _ SESSION ['logname'] [] = $ username;

Obtain a select statement to switch users.