[Patch/RFC] tr1::shared_ptr<> removal of lock, choosing thread safety

[Benjamin Kosnik]

Let's get this in.

> > apparently Benjamin also likes this approach, therefore, in general, I
> > would say let's go ahead for mainline and test it there on more arches:
> > in case of problems we have time to revert it for 4.2.0 and, in any
> > case, the "stability" requirements for tr1 are "special". Anyway, I just
> > tested it on 4-way ia64-linux too.


> > My only minor nit would be double (instead of triple) underscore for
> > __enable_shared_from_this; I would suggest renaming __lockless to
> > _S_lockfree and also __locks to _S_mutex and __unsafe to _S_single;
> > maybe _Locking_mode is better  english than _Lock_mode (your call...)
> > Maybe Benjamin wants to help here (*)...

I think this sounds good, it's more consistent with other usage.

You could also use _Lock_policy.

However, we can do the fine-tuning in-situ.

-benjamin