Introduce read-write-update locks and guards to prevent deadlocks

This converts t_rwmutex and t_rwmutex_guard into a read-write-update[*]
lock and guard, in an attempt to circumvent the various deadlocks that
were introduced with the addition of lines_mtx in 38bb6b7.

[*] For more details, see https://stackoverflow.com/a/18785300 and
http://lkml.iu.edu/hypermail/linux/kernel/0004.3/0117.html.

Note that this is not a real fix; this would require analyzing and
refactoring phone.cpp, which is well beyond my abilities.  This is at
best a workaround that appears to conveniently dodge all the deadlocks
I've encountered so far.

(It would have been more proper to introduce a separate class for this
purpose, but this would have required modifying over 80 lines just to
change one type for another.  As phone_users_mtx is the only other
instance of this class, the impact of subverting t_rwmutex directly is
minimal.)

0 files changed, 0 insertions, 0 deletions