Re: [boost] [Boost.utility]

Subject: Re: [boost] [Boost.utility]
From: Frank Mori Hess (frank.hess_at_[hidden])
Date: 2010-01-26 11:31:24

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On Tuesday 26 January 2010, Andrew Chinkoff wrote:
> Below is the typical realization of A::Instance():
>
> static A& Instance()
> {
> 	if (instance_ == NULL)
> 	{
> 		boost::mutex::scoped_lock locker(mtx_); // this is the thread safe cost!
> 		instance_ = new A();
> 	}
> 	return *instance_;
> }
>
> You should note that:
> 1) Cost for thread safe synchronization is paid only once. After instance
> had created this cost is no longer paid.
> 2) Cost for function call (A::Instance()) is replaced with smart_ptr::get()
> one.
>
> Did I miss the point?

First, you are using double-checked locking which is unsafe (google it).  
Second, using boost::mutex will open you up to problems from the static 
initialization order fiasco (google it too).  You should use boost::once to 
initialize the singleton object.
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