2007/2/5, Andreas Huber <ahd6974-spamgroupstrap@yahoo.com>:
Fabien Niñoles wrote:
Probably you should put it has a static local variable inside a protected function, like this:
//! The method returns a reference to the only dispatcher instance
static state_dispatcher const& get() { static state_dispatcher instance; return instance; }
In a multithreaded app this might work on some platforms, on others it doesn't:
Quote from http://msdn2.microsoft.com/en-us/library/s1sb61xd.aspx: "Assigning to a static local variable is not thread safe and is not recommended as a programming practice."
Although this isn't very concise wording (IIRC, the standard says that it should work for literals assigned to PODs) it seems clear that it won't work for non-PODs...
For assignation, sure, but I don't see any in my code... However, if that's bother, I think then only something like Loki Singleton pattern will do. You then need a double lock for accessing it correctly, something like this: static state_dispatcher const& get() { static state_dispatcher* pInstance; scoped_lock first_lock(m_mutex1) if (!pInstance) { scoped_lock second_lock(m_mutex2); if (!pInstance) { pInstance = new state_dispatcher; } } return *pInstance; } The problem is now one of performance, which Loki handle by making the scoped_lock class a template class policy.