Re: [Caml-list] Scoped Bound Resource Management just for C++?

[rossberg@mpi-sws.org]

> One of the benefits, in my opinion, of C++ is SBRM.  You can reason
> about the lifetime of an object and have an give yourself guarantees
> about its clean up.  The method of initialization and clean up are
> also consistent for every object in the language.

Don't believe the hype. :) Scope-bound resource management is inherently
broken, at least without sophisticated type system support. In a
higher-order language, there are various ways in which objects could escape
their scope, e.g. closures, references, exceptions. That can only mean one
of two things for SBRM:

1) Either it is not actually true, i.e. life times are not actually bound by
scope in general and you have no actual guarantees,

2) or it is unsafe, i.e. you can access an object after its life time has
ended, with potentially desastrous effects.

C++ chose (2), which is out of the question for a safe language. If your
language makes heavy use of first-class functions (and thus closures) that
strategy is a particular no-go.

Also, SBRM does not scale at all to concurrency. The underlying assumption
that all life times are somehow well-bracketed through the dynamic calling
hierarchy simply doesn't hold anymore when you have shared-state
concurrency. Getting life times right in concurrent C++ is a nightmare in my
experience, and often requires synchronizing deallocation in quite
inefficient ways (thereby effectively making it explicit, and subverting the
whole idea of tying it to scope implicitly).

/Andreas