Container insertion and removal

[dsimcha]

== Quote from Robert Jacques (sandford at jhu.edu)'s article
> > The mutation index has been used in Tango forever, and I think was in
> > Doug Lea's original container implementations.  I'm pretty sure it is
> > sound in single-threaded uses.
> No it's not. version tags + integer overflow = bug. Doug Lea knew about
> the problem and but thought it would never happen in real code. And Bill
> Gates thought no one will need more than 640k of ram. They both have been
> proven wrong.

Using a 32-bit version tag probably could lead to overflow in some corner cases,
but in the 64-bit case it can be shown that this is absurdly unlikely.  Assume
that an increment operation takes about 1 clock cycle (in reality it's more) and
that most CPUs are 10 GHz (to make things future-proof in case people figure out
how to get the clock speed race going again).

This means that a version tag could, at most, increment at about 10^10 ticks per
second.  A 64-bit unsigned int goes up to about 1.8x10^19.  This means that, even
if our program does nothing but update the version counter in an empty for loop,
it will take 1.8x10^19 / 10^10 = 1.8x10^9 seconds to overflow.  There are about
3.15x10^7 seconds in a year.

Therefore, even under very pessimistic assumptions the fastest you could overflow
a 64-bit unsigned int by incrementing it starting at zero is in about half a century.