IBM Multiple logins using the same user ID - United States ConcurrentModificationException; log in; login; multiple; userid; multiple login TECHNOTE (FAQ)

QUESTION
 "ConcurrentModificationException" and other errors may occur if the same user id is logged in to IBM WebSphere Portal multiple times.


ANSWER
WebSphere Portal has no built-in mechanism or configuration setting to limit the number of times a user id may log in. Unexpected behavior may occur if the same id is logged in more than once and this is not supported. 

"ConcurrentModificationException" and other errors may be logged.

Most of the related issues were resolved in WebSphere Portal 5.1. However, you may still encounter exceptions or side-effects if you access the Portal in multiple browser windows using the same user id, whether or not the authentication requests take place on separate physical hosts.

It may be possible to prevent multiple logins by writing custom "tracking code." Contact IBM Services for assistance to undertake such a project. WebSphere Portal Development does not have any sample code.

If you wish to write your own code, some of the issues to be aware of are (this is not an inclusive list):

-- Multiple logins may take place on different nodes in a cluster. This means some cluster-wide mechanism would have to be in place to keep track of the logged-in users. Look at the WebSphere Application Server DistributedMap interface.

-- There should be a fail-safe way to track user logout (explicit logout and session timeout). Using a session listener might be a possibility. 

-- If a user closes the browser without logging out, that user must wait for a session timeout before logging in again. Otherwise, there should be a "force simultaneous login" option in the login user interface.

For load testing, use unique user ids or virtual users.

RELATED INFORMATION
 Portal 6.1/7.0: Authentication Filters [http://publib.boulder.ibm.com/infocenter/wpdoc/v6r1/index.jsp?topic=/com.ibm.wp.ent.doc_v615/admin/adauthflt.html]
Portal 6.1: Custom Login Portlet [https://www.ibm.com/support/docview.wss?uid=swg21358508]
Restricting Multiple Sessions [http://www-10.lotus.com/ldd/portalwiki.nsf/dx/Restricting_Multiple_Sessions_in_WebSphere_Portal]





Cross reference information Segment Product Component Platform Version Edition Organizational Productivity- Portals & Collaboration WebSphere Portal End of Support Products General AIX, HP-UX, Linux, Solaris, Windows 7.0, 6.1.5, 6.1, 6.0, 5.1
Can Portal prevent the usage of simultaneous logins with the same userID? Is it possible for WebSphere Portal to limit the usage of a userID to one authenticated session as a time? In other words, prevent authenticating to Portal as "user1" from one browser and then simultaneously authenticating to Portal again as "user1" from another browser? 
WebSphere Portal has no built-in mechanism or configuration setting to limit the number of times a user id may log in. Unexpected behavior may occur if the same id is logged in more than once and this is not supported. 

"ConcurrentModificationException" and other errors may be logged.

Most of the related issues were resolved in WebSphere Portal 5.1. However, you may still encounter exceptions or side-effects if you access the Portal in multiple browser windows using the same user id, whether or not the authentication requests take place on separate physical hosts.

It may be possible to prevent multiple logins by writing custom "tracking code." Contact IBM Services for assistance to undertake such a project. WebSphere Portal Development does not have any sample code.

If you wish to write your own code, some of the issues to be aware of are (this is not an inclusive list):

-- Multiple logins may take place on different nodes in a cluster. This means some cluster-wide mechanism would have to be in place to keep track of the logged-in users. Look at the WebSphere Application Server DistributedMap interface.

-- There should be a fail-safe way to track user logout (explicit logout and session timeout). Using a session listener might be a possibility. 

-- If a user closes the browser without logging out, that user must wait for a session timeout before logging in again. Otherwise, there should be a "force simultaneous login" option in the login user interface.

For load testing, use unique user ids or virtual users.