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Subject: Re: [boost] Generic copy-on-write infrastructure in boost?
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2009-08-13 08:19:55

Jason Dictos wrote:
> I'm looking for a way to implement a project
> using some copy-on-write feature, similar to how STL strings
> use reference counters to prevent needles copying of data. Is
> there anything in boost to help me out with this?

*Some* implementations of the STL use (or used) COW strings. That is by no means ubiquitous.

Are you aware that reference counting is a pessimization rather than an optimization in the presence of multiple threads for many cases? The locking overhead required to effect reference counting is greater than the cost of copying in such cases.

Without COW, other optimizations are possible such as the small object optimization, in which the data is held within the object when small enough and moves to the free store when too large. There has been some recent discussion on this list about such things, in fact.

I'm not aware of anything that will help you implement COW, but I suspect you'd be better served by avoiding it on modern computers.

Rob Stewart robert.stewart_at_[hidden]
Software Engineer, Core Software using std::disclaimer;
Susquehanna International Group, LLP

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