The Big Kernel Lock lives on
Posted Jun 2, 2004 22:30 UTC (Wed) by
shane (subscriber, #3335)
In reply to:
The Big Kernel Lock lives on by brugolsky
Parent article:
The Big Kernel Lock lives on
Not to speak for Mr. Corbet, but I'm pretty sure he actually was
referring to having too many locks. The problem is deadlock: one thread
holding lock A, waiting for lock B; the other holding lock B, waiting for
lock A. This is the simplest example (well, holding A and waiting for A
is simpler, but you get the idea). Any circular chain of references is
possible, and causes the same problem.
This problem is easier to hit when you use many different locks. A
programmer's natural inclination is to lock each resource as you need it.
However, in order to prevent deadlock you should always lock in the same
order. Which means that if any thread ever needs lock A and lock B, it
always locks A and then lock B. This is not always optimal, as lock A
may be held for a period of time when it is not needed.
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