Re: retrieving two different objects from session (should be thesame)
Hi again, sorry for delay and thanks for help. Chuck has been absolutely right - it was a concurrency issue. As he said, it's better to store needed objects in the request than in the session. The problem is, I need an object being available for several requests, so I have to store it in the session. Now I have to find a way to store objects in session avoiding any concurrency issues... Regards, Abid Caldarale, Charles R schrieb: From: Abid Hussain [mailto:[EMAIL PROTECTED] Subject: Re: retrieving two different objects from session (should be thesame) so this means, it's specified behaviour that there is no guarantee, having an object placed in session would be the same after retrieving it after some time...? No, the object will be the same, unless the session is persisted and reloaded (what Mark T was asking about earlier), or clustering is being used. - Chuck THIS COMMUNICATION MAY CONTAIN CONFIDENTIAL AND/OR OTHERWISE PROPRIETARY MATERIAL and is thus for use only by the intended recipient. If you received this in error, please contact the sender and delete the e-mail and its attachments from all computers. - To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] -- Abid Hussain Mail: [EMAIL PROTECTED] Web: http://www.abid76.de - To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
RE: retrieving two different objects from session (should be thesame)
From: Abid Hussain [mailto:[EMAIL PROTECTED] Subject: Re: retrieving two different objects from session (should be thesame) So, this shouldn't be the reason...? Are you properly synchronizing accesses to the session for concurrent requests? Browsers will almost always generate multiple concurrent requests for the same session whenever the page being displayed has anything embedded in it (e.g., style sheets, pictures). - Chuck THIS COMMUNICATION MAY CONTAIN CONFIDENTIAL AND/OR OTHERWISE PROPRIETARY MATERIAL and is thus for use only by the intended recipient. If you received this in error, please contact the sender and delete the e-mail and its attachments from all computers. - To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: retrieving two different objects from session (should be thesame)
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Chuck, Caldarale, Charles R wrote: | Are you properly synchronizing accesses to the session for concurrent | requests? Silly question how do you do this? The result of HttpServletRequest.getSession gives you a SessionFacade which is not guaranteed to be the same as the one given to another thread accessing the same session (right?). You could synchronize using an object stored /in/ the session, but then you have to worry about that object being replaced, etc. AFAICT, there is no reliable way to synchronize access to the session other than what the container is already required to provide. - -chris -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.9 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iEYEARECAAYFAkgjD0QACgkQ9CaO5/Lv0PBDbwCfVU8ZRJXVbQzUsLOVbVfz5CrW usMAoLl5GH9TP3Qs1u/a9cNfOC4OJi7o =1EnL -END PGP SIGNATURE- - To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: retrieving two different objects from session (should be thesame)
Hi again, I'm not sure if I got the point. I would have thought that it doesn't matter if concurrent requests come in, cause: 1. There's only one request which ends up in the servlet where the described behaviour came up. The other requests which are generated by the browser wouldn't be delegated to the servlet, cause they are only requesting static resources (like pictures, etc.). 2. The webapp is normally used by a few users at the same time. 3. Whatever the number of requests is, the session stays the same, shouldn't it? Regards, Abid Caldarale, Charles R schrieb: From: Abid Hussain [mailto:[EMAIL PROTECTED] Subject: Re: retrieving two different objects from session (should be thesame) So, this shouldn't be the reason...? Are you properly synchronizing accesses to the session for concurrent requests? Browsers will almost always generate multiple concurrent requests for the same session whenever the page being displayed has anything embedded in it (e.g., style sheets, pictures). - Chuck THIS COMMUNICATION MAY CONTAIN CONFIDENTIAL AND/OR OTHERWISE PROPRIETARY MATERIAL and is thus for use only by the intended recipient. If you received this in error, please contact the sender and delete the e-mail and its attachments from all computers. - To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] -- Abid Hussain Mail: [EMAIL PROTECTED] Web: http://www.abid76.de - To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: retrieving two different objects from session (should be thesame)
Hi, The result of HttpServletRequest.getSession gives you a SessionFacade which is not guaranteed to be the same as the one given to another thread accessing the same session (right?). You could synchronize using an object stored /in/ the session, but then you have to worry about that object being replaced, etc. so this means, it's specified behaviour that there is no guarantee, having an object placed in session would be the same after retrieving it after some time...? Regards, Abid -- Abid Hussain Mail: [EMAIL PROTECTED] Web: http://www.abid76.de - To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
RE: retrieving two different objects from session (should be thesame)
From: Christopher Schultz [mailto:[EMAIL PROTECTED] Subject: Re: retrieving two different objects from session (should be thesame) Silly question how do you do this? Synchronizing on the SessionFacade will suffice for this purpose - checking if an attribute exists and then storing it if not. The container insures that accesses to the underlying attribute set itself is synchronized (we had a long and somewhat heated discussion about the necessity of that a couple of years ago). - Chuck THIS COMMUNICATION MAY CONTAIN CONFIDENTIAL AND/OR OTHERWISE PROPRIETARY MATERIAL and is thus for use only by the intended recipient. If you received this in error, please contact the sender and delete the e-mail and its attachments from all computers. - To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
RE: retrieving two different objects from session (should be thesame)
From: Abid Hussain [mailto:[EMAIL PROTECTED] Subject: Re: retrieving two different objects from session (should be thesame) so this means, it's specified behaviour that there is no guarantee, having an object placed in session would be the same after retrieving it after some time...? No, the object will be the same, unless the session is persisted and reloaded (what Mark T was asking about earlier), or clustering is being used. - Chuck THIS COMMUNICATION MAY CONTAIN CONFIDENTIAL AND/OR OTHERWISE PROPRIETARY MATERIAL and is thus for use only by the intended recipient. If you received this in error, please contact the sender and delete the e-mail and its attachments from all computers. - To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
RE: retrieving two different objects from session (should be thesame)
From: Abid Hussain [mailto:[EMAIL PROTECTED] Subject: Re: retrieving two different objects from session (should be thesame) 1. There's only one request which ends up in the servlet where the described behaviour came up. Only true if the user never opens two windows/frames targeting the same servlet - and you have no control over that. The sporadic nature of the failure would indicate you have some form of concurrency problem. 2. The webapp is normally used by a few users at the same time. The number of users doesn't matter, since each has a separate session. 3. Whatever the number of requests is, the session stays the same, shouldn't it? Yes, which creates the need for synchronization due to the possibility of multiple concurrent requests for the same session. - Chuck THIS COMMUNICATION MAY CONTAIN CONFIDENTIAL AND/OR OTHERWISE PROPRIETARY MATERIAL and is thus for use only by the intended recipient. If you received this in error, please contact the sender and delete the e-mail and its attachments from all computers. - To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: retrieving two different objects from session (should be thesame)
-BEGIN PGP SIGNED MESSAGE-
Hash: SHA1
Chuck,
Caldarale, Charles R wrote:
| From: Christopher Schultz [mailto:[EMAIL PROTECTED]
| Subject: Re: retrieving two different objects from session
| (should be thesame)
|
| Silly question how do you do this?
|
| Synchronizing on the SessionFacade will suffice for this purpose -
| checking if an attribute exists and then storing it if not. The
| container insures that accesses to the underlying attribute set itself
| is synchronized (we had a long and somewhat heated discussion about the
| necessity of that a couple of years ago).
Okay, cool. I just assumed that
HttpSession session = request.getSession();
Object myObject;
synchroinzed(session) {
~ myObject = session.getAttribute(myObject);
~ if(null == myObject)
~ {
~ myObject = // get new object
~ session.setAttribute(myObject, myObject);
~ }
}
could not be considered threadsafe. Fortunately, I have never had to
write code such as this :)
Can you explain how this is done? My tenuous understanding of session
handling in Tomcat is that HttpServletRequest.getSession roughly returns:
new StandardSessionFacade(theRealSessionObject)
...which means that the real session is hidden behind the facade
(makes sense), but that the object implementing the session is therefore
unavailable for synchronization purposes. Since synchronized() isn't a
function call, it can't be virtualized and/or intercepted, so wrapping
the session in a facade actually eliminates the possibility for
synchronization.
I must have this wrong. It's tough to sit down with the code and figure
everything out, though. :(
- -chris
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RE: retrieving two different objects from session (should be thesame)
From: Christopher Schultz [mailto:[EMAIL PROTECTED] Subject: Re: retrieving two different objects from session (should be thesame) My tenuous understanding of session handling in Tomcat is that HttpServletRequest.getSession roughly returns: new StandardSessionFacade(theRealSessionObject) Don't think so. I just took a look at the code, and it appears to me that the facade is only created once per session, not once per getSession() call. I did think of another issue with this situation: if the attribute under discussion is only relevant for one particular request, it's a design flaw to store it in the session. It should be saved in the request instead, thereby avoiding any concurrency issues. Since the OP didn't really give us much information about the lifetime of the attribute, I just assumed it had session scope. - Chuck THIS COMMUNICATION MAY CONTAIN CONFIDENTIAL AND/OR OTHERWISE PROPRIETARY MATERIAL and is thus for use only by the intended recipient. If you received this in error, please contact the sender and delete the e-mail and its attachments from all computers. - To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: retrieving two different objects from session (should be thesame)
are you proposing synchronized access to facade object ? M- - Original Message - From: Christopher Schultz [EMAIL PROTECTED] To: Tomcat Users List users@tomcat.apache.org Sent: Thursday, May 08, 2008 10:33 AM Subject: Re: retrieving two different objects from session (should be thesame) -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Chuck, Caldarale, Charles R wrote: | Are you properly synchronizing accesses to the session for concurrent | requests? Silly question how do you do this? The result of HttpServletRequest.getSession gives you a SessionFacade which is not guaranteed to be the same as the one given to another thread accessing the same session (right?). You could synchronize using an object stored /in/ the session, but then you have to worry about that object being replaced, etc. AFAICT, there is no reliable way to synchronize access to the session other than what the container is already required to provide. - -chris -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.9 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iEYEARECAAYFAkgjD0QACgkQ9CaO5/Lv0PBDbwCfVU8ZRJXVbQzUsLOVbVfz5CrW usMAoLl5GH9TP3Qs1u/a9cNfOC4OJi7o =1EnL -END PGP SIGNATURE- - To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] - To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: retrieving two different objects from session (should be thesame)
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Chuck, Caldarale, Charles R wrote: | From: Christopher Schultz [mailto:[EMAIL PROTECTED] | Subject: Re: retrieving two different objects from session | (should be thesame) | | My tenuous understanding of session handling in Tomcat | is that HttpServletRequest.getSession roughly returns: | | new StandardSessionFacade(theRealSessionObject) | | Don't think so. I just took a look at the code, and it appears to me | that the facade is only created once per session, not once per | getSession() call. Okay. I was looking around for that before I sent my message, but I started to get lost in the Request versus Request versus StandardRequest versus HttpSevrletRequest versus whatever else is in there. | I did think of another issue with this situation: if the attribute | under discussion is only relevant for one particular request, it's a | design flaw to store it in the session. Definitely. | It should be saved in the | request instead, thereby avoiding any concurrency issues. Since the OP | didn't really give us much information about the lifetime of the | attribute, I just assumed it had session scope. Yeah. I'm wondering if he's using some type of form processing library that re-writes the form object in the session each time. Struts, for example, allows you to define forms for processing to have session scope, and it will create the object and stuff it into the session for you. There's no guarantee that the form object itself will survive multiple requests, though the form should always be available. It's possible that a new object would be created and actually replace the in-session object, though I don't think that's actually how it's implemented. - -chris -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.9 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iEYEARECAAYFAkgjIYAACgkQ9CaO5/Lv0PCNWQCffAxYIqwob9qA6NfyItOq+Jwm CNkAoKWbvtxoyJLZF7sD602CHltbq802 =ZA/o -END PGP SIGNATURE- - To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: retrieving two different objects from session (should be thesame)
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Martin,
Martin wrote:
| are you proposing synchronized access to facade object
No, I'm suggesting that it should be easy enough to:
synchronized(session) {
~ // do something that requires exclusive session access
}
~From what Chuck says, it seems like that is possible.
- -chris
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