> Thanks for your reply.
> I changed the format to plain text.
> For the question, suppose that process p0 held the lock of object A, and the wait queue for A is p1,p2,p3,...., that process p1 is the first waiter in the queue.
> Since p1 is in the wait queue, the lock p1 requests must be conflict with the lock p0 held.
> That is to say, if p0 wants to lock A again, then p0 will be put before p1, and p0 will be at the head of the queue. Why do we need to find the first waiter which conflicts p0? I think that p0 must be added at the head of the wait queue.
> For your example, p0 has a read lock and wants an exclusive lock.
> Since p0 has a read lock, then in the queue, p1 must wait an exclusive lock.
> Then p0 will be put before p1, and p0 will be at the head of the queue.
> Is there anything I misunderstood?
I am guessing that p0 is put at the head _only_ if there are conflicting
locks so that p0 does not starve other waiting processes.
Bruce Momjian http://candle.pha.pa.us
+ If your life is a hard drive, Christ can be your backup. +
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