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From: Hurd, Matthew (hurdm_at_[hidden])
Date: 2004-06-08 19:13:57

> Behalf Of Eric Niebler
> Sent: Wednesday, 9 June 2004 9:15 AM
> To: boost_at_[hidden]
> Subject: [boost] Re: Thread lib (good reason for static)
> Hurd, Matthew wrote:
> >>Behalf Of scott
> >>Assume use of a technique like the following (think this has been
> >>presented as "object shim"?);
> >>
> >>T &
> >>anastasia()
> >>{
> >> static T *p = new T;
> >> return *p;
> >>}
> >>
> >>as a means of dealing with global construction issue, i.e. instead
> >>of expressions like "anastasia.data_member" the usage is
> >>"anastasia().data_member". Also assume that some of these global
> >>objects (i.e. shims) deploy mutexes for MT reasons. What happens
> >>when there is more that one thread running around making calls
> >>to shims? Instantiation of the global itself becomes an MT issue.
> >
> >
> > That's what the double-checked locking pattern for singletons is
> >
> > Regards,
> >
> > Matt Hurd.
> No, the double-checked locking pattern is only good as the subject of
> talks describing why it's not good for anything.

Thanks. They are good notes.

I'm aware of the portability issues. Doesn't mean you can't have valid
platform specific singleton implementations that use the double checked
locking pattern. The performance of the approach is too important to
give up. Locking is slow.

There are a lot of things you can't do portability in C++ which is one
rationale for having libraries :-)

Matt Hurd.

Matt Hurd

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