Milan Siebenbürger created MYFACES-4660:
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Summary: WebSockets - view destroying + multiple tabs/windows
Key: MYFACES-4660
URL: https://issues.apache.org/jira/browse/MYFACES-4660
Project: MyFaces Core
Issue Type: Bug
Components: General
Affects Versions: 4.0.2, 4.0.1, 4.0.0, 5.0.0
Reporter: Milan Siebenbürger
Hello,
We have identified two (hopefully minor) bugs while using WebSockets.
1. destroying SessionScope channelToken when destroying ViewScope bean
If the user reaches the NUMBER_OF_VIEWS_IN_SESSION limit, the ViewScope bean
(which holds channelTokens) is automatically destroyed (@PreDestroy).
Additionally, any channelToken from the parent sessionScope is destroyed, even
if it is still in use. Unfortunately, this destruction occurs after a new view
is created, so the component is rendered, the WebSocket session is connected,
but the channelToken in the WebsocketScopeManager is destroyed.
The solution to this issue could be simple. The destruction of the sessionScope
channelToken could be left to the automatic destruction of the SessionScope. We
have been testing this solution for several weeks, and it seems to be working
fine.
2. using application in multiple tabs / browser windows (with same http session)
When a user is using the application in more than one tab/window within the
same HTTP session, the user session channels are duplicated (with the same
channelToken) and connected to the same user identification, resulting in two
or more WebSocket sessions. Push messages are then sent to all tokens/sessions.
So far, everything is working as expected.
However, when one of the views is destroyed (i.e., a tab/window is closed), the
connected WebSocket session is also destroyed (which is expected).
Unfortunately, this also will cause user connection to be removed . Since we
don't track how many times the user is using this particular channelToken, the
WebSocket connections in the other tabs/windows are also disrupted.
A potential solution to this issue could involve tracking the number of times
the user starts using the channelToken. We could then remove the user
connection after all instances of its usage are destroyed, or, alternatively,
when the SessionScope object is destroyed.
Unfortunately, implementing this solution would cause a breaking change. It
would involve replacing the Set holding channelTokens with a HashMap that also
keeps track of the number of usages (refer to WebsocketSessionManager.java:62).
Since the method getUserMap is public and may be used by others (such as
ourselves, for implementing WebSocket heartbeat), they would need to update
their code accordingly with the new version of MyFaces. An alternative approach
could be implemented using another collection to hold the usage count of
channelTokens. However, this method may not be as elegant, although it would
not necessitate users to modify their applications.
So, the questions:
* which of these to implement?
* and to which version (5.0? or 4.X?)
Of course, I will prepare the changes in the form of a pull request to check
the changes
Milan
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