dynalink wrote: > Works great! How thread safe is this? Looks as thread safe as your version, where you could end up calling m_X.reset(new X) simultaneosly if two threads created a B at the same time. IOW, not much. :-)
All shared_ptr/weak_ptr operations have the same thread safety level, i.e. multiple reads are safe, writes need to be exclusive. You'll probably need a mutex lock in A::create to make B thread-neutral. > "Peter Dimov" <[EMAIL PROTECTED]> wrote in message > 001301c2d12c$30c1d210$1d00a8c0@pdimov2">news:001301c2d12c$30c1d210$1d00a8c0@pdimov2... >> dynalink wrote: >>> I need to create a single instance of X and have it disappear when >>> the >>> final B pointer goes out of scope. The problem with this code is >>> that A::m_X immediately bumps the ref count and only goes out of >>> scope on termination. >>> >>> Here's a simple example: >>> >>> class X; // defined elsewhere; in my case wraps a classic C >>> structure. typedef boost::smart_ptr<X> X_ptr; >>> >>> struct A { >>> static X_ptr create() { if (!m_X.get()) m_X.reset(new X); return >>> m_X; } static X_ptr m_X; >>> }; >>> >>> struct B { >>> B() : m_A(A::create()){} >>> X_ptr m_A; >>> }; >> >> You need to keep a weak_ptr in A. >> >> struct A >> { >> static X_ptr create() >> { >> if(X_ptr px = make_shared(wp_)) >> { >> return px; >> } >> else >> { >> X_ptr px(new X); >> wp_ = px; >> return px; >> } >> } >> >> static weak_ptr<X> wp_; >> }; _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
