Question

If I have to write a singleton class in C++ I will be using a static variable, private constructor & a public static function that returns an object of class. However in Multithreaded environments the code will have problems. In order to avoid multiple threads access the same variable at the same time, is Boost threads best mechanism to use for synchronization? I mean for setting/unsetting a lock/mutex across the resource. Is there anything else inbuilt in C++ standard library where in I dont have to download boost, build stuff etc? I have heard of C++ Ox but dont know much.

Answer 1

C++98/03 have nothing to support threads at all. If you’re using a C++98 or 03 compiler, you’re pretty much stuck with using Boost, or something (more or less) OS-specific, such as pthreads or Win32’s threading primitives.

C++11 has a reasonably complete thread support library, with mutexes, locks, thread-local storage, etc.

I feel obliged to point out, however, that it may be better to back up and do a bit more thinking about whether you need/want a Singleton at all. To put it nicely, the singleton pattern has fallen out of favor to a large degree.

Edit: Rereading this, I kind of skipped over one thing I’d intended to say: at least when I’ve used them, any/all singletons were fully initialized before any secondary thread was started. That renders concern over thread safety in their initialization completely moot. I suppose there could be a singleton that you can’t initialize before you start up secondary threads so you’d need to deal with this, but at least right off it strikes me as a rather unusual exception that I’d deal with only when/if absolutely necessary.