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From: Adam Boyle <aboyle@valsphere.com>
To: "user@cayenne.apache.org" <user@cayenne.apache.org>
Subject: Re: ROP: detecting that my client connection has timed out
Thread-Topic: ROP: detecting that my client connection has timed out
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Date: Fri, 8 Apr 2016 05:06:16 +0000
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Thanks for the response. I could be overlooking it, but I don't see an answ=
er to my central question: how can I detect that the client has timed out? =
The nature of our application prevents us from using a keep-alive type solu=
tion; it is meant to be used in highly regulated environments (which is one=
 of the reasons I chose Cayenne ROP: it provides a way to hide the database=
 details from the users). Even if I could use an auto-reconnect solution, I=
 would still need to be able to detect that the connection has timed out, a=
nd I have failed to find a way to actually detect that.

I suppose that another (less-hacky) way I could approach this would be to l=
ogically detect a "timeout" by keeping the actual connection alive and stor=
ing login session info in the database and updating it with the current dat=
e time every time a Cayenne action is performed. This code would check for =
a timeout beforehand and prompt the user to re-authenticate before performi=
ng said action. The main problem there is maintainability; I'd have to add =
this check to every place I intend to submit any sort of Cayenne action unl=
ess there is a way to hook this sort of check into the ObjectContext.

Does anyone know of a better way? Perhaps some advice for this novice enter=
prise developer?

Thanks again,
Adam

________________________________________
From: Aristedes Maniatis <ari@maniatis.org>
Sent: Friday, April 8, 2016 12:30 AM
To: user@cayenne.apache.org
Subject: Re: ROP: detecting that my client connection has timed out

On 8/04/2016 1:28pm, Adam Boyle wrote:
> Is there a simple way of detecting that the connection is dead so that I =
can prompt the user to reconnect?

I don't think you need to prompt the user if you keep the user's authentica=
tion details in memory. Just create a new session with them.


> On a related note, what happens to the existing client ObjectContext obje=
cts that are in use if the connection is able to be re-established? Are the=
 uncommitted PersistentObjects previously created in those contexts lost fo=
rever?

Those contexts are no longer associated with a session on the server (once =
your session times out). So you either have to recognise that a user is con=
necting again after a connection error and give them a handle on the same s=
ession id they had last time, or else start a new session and lose the old =
contexts.

The problem is: can you be sure the state of those contexts still make sens=
e?


> The only (hacky) solution I can think of is to actually run a keep-alive =
thread to periodically send a low-latency query to Cayenne to keep the ROP =
session active and separately track application activity and prompt the use=
r to enter their password if a certain period of time has passed with no ac=
tivity. The problem that I see with an approach like that is that there are=
 lots of ways that activity could be missed, the application is not truly t=
iming out, and it really doesn't address the underlying problem which is th=
at sessions need to time out for a reason and there doesn't seem to be a wa=
y to detect such a timeout.

Well this is outside Cayenne itself, but part of the reason we recently did=
 the work in trunk (CAY-2065) to untangle Cayenne from Hessian and from the=
 HTTP layer. Then you can manage the session more easily yourself to do wha=
tever you want.

For example, we have a ping every minute from the client that:

* keeps the session alive (we don't want the session to die just because th=
e user went to have lunch)
* allows us the keep the server-side session timeout quite low (good to exp=
ire sessions for users who dropped off the network without a proper logout)
* allows the server to track which users are having network issues

In the last six months we've been doing a bunch of work with ActiveMQ/STOMP=
 which might eventually replace that ping. That way we have two way server-=
client communication and the server can quickly see which clients have lost=
 network connection without a ping.


Nice to see a fellow Cayenne ROP user. There aren't many of us and it is re=
ally a very powerful bit of functionality.


Ari


--
-------------------------->
Aristedes Maniatis
GPG fingerprint CBFB 84B4 738D 4E87 5E5C  5EFA EF6A 7D2E 3E49 102A=