Re: [boost] [Boost.utility]

Subject: Re: [boost] [Boost.utility]
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2010-01-26 11:30:04

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.

That code has a race condition, so it appears more efficient than it should.

> 2) Cost for function call (A::Instance()) is replaced with
> smart_ptr::get() one.
>
> Did I miss the point?

Yes.  The smart pointer's operators are inlined functions that merely access a pointer data member.  Zero overhead.  Your function cannot be inlined and, depending upon how you manage the synchronization, it can be fairly costly, but most certainly includes function call overhead.

_____
Rob Stewart                           robert.stewart_at_[hidden]
Software Engineer, Core Software      using std::disclaimer;
Susquehanna International Group, LLP  http://www.sig.com

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