This section covers some locking fundamentals, as well as some information on
locking as it is used in Asterisk.  It describes some of the ways that are used
and could be used to achieve deadlock avoidance.  It also demonstrates the
unfortunate conclusion that with the use of recursive locks, none of the
constructs in use today are failsafe from deadlocks.  Finally, it makes some
recommendations for new code being written.  As proper locking strategies is a
complex subject, this section still has room for expansion and improvement.

This is a result of collaboration between Luigi Rizzo and myself on the 
asterisk-dev mailing list.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@127363 65c4cc65-6c06-0410-ace0-fbb531ad65f3