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From bugzi...@apache.org
Subject DO NOT REPLY [Bug 7681] New: - Tomcat does not work properly in multithread environment
Date Tue, 02 Apr 2002 07:50:43 GMT
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http://nagoya.apache.org/bugzilla/show_bug.cgi?id=7681

Tomcat does not work properly in multithread environment

           Summary: Tomcat does not work properly in multithread environment
           Product: Tomcat 4
           Version: 4.0.4 Beta 2
          Platform: PC
        OS/Version: Windows NT/2K
            Status: NEW
          Severity: Major
          Priority: Other
         Component: Servlet & JSP API
        AssignedTo: tomcat-dev@jakarta.apache.org
        ReportedBy: marcin_ol@poczta.onet.pl


This bug exists also in version 4.01, so it is much possible it exists in all 
4.x versions.
I found that Tomcat has a quite serious bug, that causes it not working 
correctly when more than one thread is processing requests.
The bug appears when the welcome file is a FRAMESET definition file, which
does not access session object nor use beans - the first access of session is 
by session-scope bean definition in pages, that are loaded in frames from this 
frameset.
Now, since browser makes requests for frames concurrently, each frame is 
usually processed by different Tomcat thread. And there is a problem: if two 
frames uses the same bean (of session scope), it often gets initialized 
twice !!! (it usually happens when the bean communicates with database during 
init, or makes other time-consumpting operation).
The workaround is to make welcome file access the session (e.g. by setting some 
attribute or by reading session ID) - then the bean gets instantiated only once.

The reason for this bug is in servlet generated from JSP: there are parts that 
are synchronized on "session" object - it does not make any sense, since 
session is an instance of StandardSessionFacade, which is a page-level object - 
it is created as new object on every page, and every time the page is accessed 
(just print it on System.out - every time, different address is printed); it 
would make sense if the synchronization was on HttpSession object encapsulated 
by StandardSessionFacade.

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