[RIVER-142] concurrency problem in DGC lease expiration handling

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: jtsk_2.0
• Fix Version/s: River_2.2.0
• Component/s: net_jini_jeri
• Bugtraq ID: 4848840
• Assignee: Peter Firmstone
• Reporter: Peter Jones
• Created: 27/Jul/07 22:05
• Updated: 08/Feb/12 08:35
• Resolved: 20/Jun/11 10:23

Description

Bugtraq ID 4848840

In the server-side DGC implementation's thread that check's for lease expirations (com.sun.jini.jeri.internal.runtime.ObjectTable.LeaseChecker.run), it checks for them while synchronized on the overall lease table, but it delays notifying the expired leases' individual registered Targets about the expirations until after it has released the lease table lock. This approach was taken from the JRMP implementation, which is that way because of the fix for 4118056 (a previous deadlock bug-- but now, I'm thinking that the JRMP implementation has this bug too).

The problem seems to be that after releasing the lease table lock, it is possible for another lease renewal/request to come in (from the same DGC client and for the same remote object) that would then be invalidated by the subsequent Target notification made by the lease expiration check thread-- and thus the client's lease renewal (for that remote object) will be forgotten. It would appear that the synchronization approach here needs to be reconsidered.

( Comments note: )

In addition to the basic problem of the expired-then-renewed client being removed from the referenced set, there is also the problem of the sequence table entry being forgotten-- which prevents detection of a "late clean call".

Normally, late clean calls are not a problem because sequence numbers are retained while the client is in the referenced set (and there is no such thing as a "strong dirty"). But in this case, with the following order of events on the server side:

1. dirty, seqNo=2
2. (lease expiration)
3. clean, seqNo=1

The primary bug here is that the first two events will leave the client missing from the referenced set. But the secondary bug is that even if that's fixed, with the sequence number forgotten, the third event (the "late clean call") will still cause the client to be removed from the referenced set.

Sub-Tasks

• DGC leaks threads: Closed