On Mon, 7 Mar 2011 04:37:40 +0200 "Peter Dimov" <pdimov@pdimov.com> wrote:
Chad Nelson wrote:
The only concrete complaint that people could give me about CoW was that code using it couldn't be made thread-safe, which is true. So I made a way to instruct the library to force all integer objects to have unique storage before they're returned to user code, and made it the default to prevent unpleasant client-code surprises.
I don't think that this is enough to prevent surprises. If someone does
thread t( f, x );
where x is an integer, the thread would receive a shared copy of x. The user would need to explicitly call the copy constructor with a second argument of true to avoid that.
You'd think so, but so long as that thread class takes the integer parameter as either a constant reference or by value, or is the only one thread accessing it if it's passed by non-constant reference, that's not the case. The copy constructor will automatically deep-copy the object, unless the client code explicitly tells it to use external copy-on-write -- that's the only time the second argument to the copy constructor would come into play.
Just use detail::atomic_count until C++0x atomics arrive in numbers. :-)
Not sure where I'd find detail::atomic_count. Has Boost.Atomic been accepted? I don't see it in the 1.46 docs. -- Chad Nelson Oak Circle Software, Inc. * * *