code 128 generator c# The resource list in C#.NET

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The resource list
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What we don't know yet is what locks these two processes were holding when the deadlock occurred. That s where the third part of the deadlock graph the resource list comes in. The resource list lists all of the locks involved in the deadlock, along with which process had them and which process wanted them. The first entry in the resource list refers to the key lock on the primary key of the Users table. We know, from the first section of the deadlock graph, that this is what session ID 53 was waiting for:
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keylock hobtid=72057594038845440 dbid=6 objectname=WF.dbo.Users indexname=PK__Users id=lock800c0f00 mode=X associatedObjectId=72057594038845440 owner-list owner id=process809f8748 mode=X waiter-list waiter id=process803294c8 mode=S requestType=wait
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Process process809f8748, which is session ID 55, owned that lock in exclusive mode. Process process803294c8 requested the lock in shared mode and had to wait. The second entry in the resource list refers to the page lock on the Threads table. We know from the first section that this is what session ID 55 was waiting for:
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Tracing the deadlock
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pagelock fileid=1 pageid=351 dbid=6 objectname=WF.dbo.Threads id=lock83255f80 mode=IX associatedObjectId=72057594038910976 owner-list owner id=process803294c8 mode=IX waiter-list waiter id=process809f8748 mode=S requestType=wait
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The process process803294c8, which is session ID 53, owned that resource in intentexclusive mode and hence process process809f8748 (session ID 55) had to wait.
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An intent-exclusive (IX) lock is taken by a process before an exclusive lock and at a lower level of lock granularity, and is taken to signal the intention to take an exclusive lock; hence the name.
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The two most common values for requestType are wait and convert. A value of wait indicates that a new lock has been requested; convert indicates that the process already has a lock on that resource in one mode and requested to convert the lock into a different mode. A typical example would be when a process has a shared lock and wishes to convert it to exclusive. The conversion can only occur if there are no locks on the resource that are incompatible with the new lock mode for example in the repeatable read isolation level, where a row is selected and then updated within a transaction.
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The big picture
Now the full picture of the events that lead up to and resulted in the deadlock is clear. The process with a session ID of 53, while running the procedure ViewThread, began an explicit transaction and did a data modification on the Threads table. Later in the same transaction, it tried to do a select on the Users table, which was blocked. The second process, session ID 55, ran the procedure ViewForum. Within the procedure, it began an explicit transaction and did a data modification on the Users table. Following that, it attempted to run a select on the Threads table, which was blocked. This deadlock turns out to be a case of objects accessed in different orders from different places. Although fixing the code is beyond the scope of this chapter, it turns out that reordering the queries in one of those procedures, so that the objects are accessed in the same order in both, prevents the deadlock completely. Changing the isolation level to Snapshot or Read Committed Snapshot will also prevent the deadlock, because in the optimistic concurrency model, writers don t block readers. Again, a discussion on snapshot isolation is beyond the scope of this chapter.
Summary
The deadlock graph is the key to understanding and resolving deadlocks. The list of resources locked shows the state of events before the deadlock. The information provided about the process s state at the time of the deadlock, including locks requested and the process s input buffers, shows the cause of the deadlock clearly.
Summary
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