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From "Scott O'Bryan (JIRA)" <...@myfaces.apache.org>
Subject [jira] [Comment Edited] (TRINIDAD-2278) HttpSession inside a synchronized block in the class TokenCache of trinidad-impl-1.0.10.jar could cause to deadlock while used with WAS 7
Date Wed, 20 Jun 2012 22:51:43 GMT

    [ https://issues.apache.org/jira/browse/TRINIDAD-2278?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13397968#comment-13397968
] 

Scott O'Bryan edited comment on TRINIDAD-2278 at 6/20/12 10:51 PM:
-------------------------------------------------------------------

I think you're right on here Reshmi.  However the syncronization is needed for other reasons.
 Although the HttpSession itself will not run into threading issues, that is not to say that
the code which uses it won't.

Truth be told, aside from the deadlock issue, this isn't even guaranteed to work because there
is no guarentee the session instance is the same between threads.

In later Trinidad releases, I would say this should be replaced with a lock.  Since session
is thread safe, we do not have to worry about any caching issues from the object, so a simple
lock around the code would suffice.  For this branch of Trinidad, I suppose you could syncronize
on the tokenCache itself or create another lock object to syncronize on.

Do keep in mind that 1.0 is no longer maintained, but I do invite you to provide a patch here
that other people can apply to the latest trunk manually.  Thanks for your interest.
                
      was (Author: darkarena):
    I think you're right on here Reshmi.  However the syncronization is needed for other reasons.
 Although the HttpSession itself will not run into threading issues, that is not to say that
the code which uses it won't.

Truth be told, aside from the deadlock issue, this isn't even guaranteed to work because there
is no guarentee the session instance is the same for two sessions.

In later Trinidad releases, I would say this should be replaced with a lock.  Since session
is thread safe, we do not have to worry about any caching issues from the object, so a simple
lock around the code would suffice.  For this branch of Trinidad, I suppose you could syncronize
on the tokenCache itself or create another lock object to syncronize on.

Do keep in mind that 1.0 is no longer maintained, but I do invite you to provide a patch here
that other people can apply to the latest trunk manually.  Thanks for your interest.
                  
> HttpSession inside a synchronized block in the class TokenCache of trinidad-impl-1.0.10.jar
could cause to deadlock while used with WAS 7
> -----------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: TRINIDAD-2278
>                 URL: https://issues.apache.org/jira/browse/TRINIDAD-2278
>             Project: MyFaces Trinidad
>          Issue Type: Bug
>    Affects Versions: 1.0.10-core
>            Reporter: Reshmi Choudhury
>
> Hi,
> We are using trinidad-impl-1.0.10.jar in our product. I see that HttpSession is used
in a synchronized block in the class TokenCache of trinidad-impl-1.0.10.jar. Could you please
clarify if this could cause to deadlock while used with WAS 7.
> Please find the below code snippet for your quick reference.
> static public TokenCache getTokenCacheFromSession( FacesContext context,  String  cacheName,
 boolean  createIfNeeded,  int   defaultSize)   {
>     ExternalContext external = context.getExternalContext();
>     Object session = external.getSession(true);
>     assert(session != null);
>     TokenCache cache;
>     // Synchronize on the session object to ensure that
>     // we don't ever create two different caches
>     synchronized (session)
>     {
>       cache = (TokenCache) external.getSessionMap().get(cacheName);
>       if ((cache == null) && createIfNeeded)
>       {
>         // Seed the token cache with the session ID (if available)
>         int seed = 0;
>         if (_USE_SESSION_TO_SEED_ID)
>         {
>           if (session instanceof HttpSession)
>           {
>             String id = ((HttpSession) session).getId();
>             if (id != null)
>               seed = id.hashCode();
>           }
>         }
>         cache = new TokenCache(defaultSize, seed);
>         external.getSessionMap().put(cacheName, cache);
>       }
>     }
>     return cache;
>   }
> This information is required as IBM informs the developer not to synchronize the session
or it will cause deadlocks. WAS 7 implements the Servlets 2.5 specification and manages the
thread safety for any modification to the session map. Please refer to the URL http://pic.dhe.ibm.com/infocenter/wasinfo/v7r0/index.jsp?topic=/com.ibm.websphere.nd.multiplatform.doc/info/ae/ae/uprs_rsession_manager.html
for more details. This URL contains this text:
> “Applications cannot synchronize session objects inside of their servlets or Java Server
Pages because a deadlock with the session manager may occur. The deadlock occurs because the
session manager does not expect the use of more than one locking mechanism”
> Here is an excellent article on this topic, which explains when explicit synchronization
is needed in the application code and when the servlet container's locking mechanism is sufficient:
> http://www.ibm.com/developerworks/library/j-jtp09238/index.html
>  
> It would be really helpful if we receive the information at the earliest as this is priority
at our end.
> Thanks in advance.
> Regards,
> Reshmi

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