[Threads-devel] shared mutex locking discipline

From: Frank Mori Hess (fmhess_at_[hidden])
Date: 2008-04-13 13:01:17

I'm curious if there is any theory on how to avoid deadlock when using a 
shared mutex?  Having a well-defined locking order works well for an 
ordinary mutex, but things get messy with a shared mutex.  For example, if 
we have mutexes A and B then the locking sequence

1) shared lock A
2) unique lock B
3) upgrade to unique lock A

will deadlock against

shared lock A (between steps 2 and 3 above)
unique lock B

it will also deadlock against

unique lock B (between steps 1 and 2 above)
unique lock A

however, it will not deadlock against

unique lock A
unique lock B

-- 
Frank