Re: [boost] [thread] Proposal for thread safe initialization of local statics

From: Peter Dimov (pdimov_at_[hidden])
Date: 2006-10-06 08:00:21

Roland Schwarz wrote:
> Anthony Williams wrote:
>> On Windows we don't need two calls to call_once, as my
>> implementation allows passing an arbitrary functor, which can
>> therefore have state (e.g. use bind to pass parameters).
>
> Hmm, I remember there was a sound reason why Bill Kempf ommitted
> parameters deliberately. Not sure about this, I will need to try
> to find the respective discussion thread.

No, there is none. He just followed pthread_once without realizing (at 
first) that he won't be able to use it directly on all platforms.

>> Your code demonstrates how we could provide the same facility with
>> pthreads, as an extension to call_once. Incidentally, whilst we're
>> thinking about this, the POSIX spec says:
>
> Indeed I have shamelessly stolen the idea from looking at Bill Kempfs
> call_once implementation for pthreads. He is using this there also,
> altough I think, superfluously.

Not superfluously. pthread_once accepts an extern "C" function. Test on a 
platform where extern "C" functions are incompatible with extern "C++" 
functions (Comeau C++) and you'll see why the second call is needed. 
Incidentally, that second call also enables arbitrary function objects in 
addition to ordinary C++ functions. :-)