You can't lock two locks willy-nilly like this. So ideally what I'd like to do is create a generic lock function that will lock multiple locks without danger of deadlock:
template <class TryLock1, class TryLock2> void lock(TryLock1& l1, TryLock2& l2);
and maybe also:
template <class TryLock1, class TryLock2, class TryLock3> void lock(TryLock1& l1, TryLock2& l2, TryLock3& l3);
Yep, those would be useful additions to Boost.Thread IMO.
Problem: With the current interface, my "generic" lock algorithm is no longer generic. It has to know about read_lock() and write_lock(), even though these concepts have absolutely nothing to do with how you lock two locks while avoiding deadlock.
Ah, that's what happens from looking at my not so good test case, rather than the docs :-) try_read_write_mutex does have member typedefs try_read_lock and try_write_lock, which do what you want them to, I just happened to use a different locking primitive because it was easier to change the test code around to test different combinations of readers and writers.
Sorry, but: Houston, we have an even bigger problem...
Not this time, still it was big enough to begin with :-( John.