Re: Proposed C++ extension

[Nathan Sidwell <nathan at codesourcery dot com>]

Niall Douglas wrote:

> Why? Because C++ doesn't support multithreading very well. I have a
> number of implicitly shared classes for which I had to disable
> implicit sharing because of the potential of data corruption as it's
> impossible to synchronise all users of the implicit data without
> running through a mutex each time.
> 
> Unfortunately disabling implicit sharing creates performance problems
> in something like a string class. If we had a special copy
> constructor for temporary objects, we could do ptr copies for the
> temporary objects and the real copy constructor for the final object.
> Obviously, optimisation can decide when user created local objects
> are unnecessary, and hence optimise them into temporary land.
can't what you want be done with,

	class unique_t { ... };
	class shared_t : public unique_t {... locks in here };

	void somefunc (unique_t arg);
now a unique_t copy ctor is invoked.

your problem description is too vague. I can't tell if you want a magic
bullet which will make your program multithreadable, or if you want some way
of saying 'this is a unique object, no need to lock it'.

nathan
-- 
Dr Nathan Sidwell   ::   http://www.codesourcery.com   ::   CodeSourcery LLC
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