The document is about a design pattern called double locking, which is
especially suitable for singleton objects in multithreaded environments.
The pattern is essentially this:
static Singleton *instance (void)
{
// First check
if (instance_ == 0)
{
// Ensure serialization (guard
// constructor acquires lock_).
Guard<Mutex> guard (lock_);
// Double check.
if (instance_ == 0)
instance_ = new Singleton;
}
return instance_;
// guard destructor releases lock_.
}
The guard mutex is only accessed in the initialization phase of the singleton.
Once instance_ is set the guard does not need to be queried anymore.
Richard
_______________________________________
Von: [email protected]
[mailto:[email protected]] Im Auftrag von Robert
Osfield
Gesendet: Dienstag, 17. März 2009 11:07
An: OpenSceneGraph Users
Betreff: Re: [osg-users] Multithreading crash duetoosgDb::Registry::instance()
2009/3/17 Schmidt, Richard <[email protected]>
http://www.cs.wustl.edu/~schmidt/PDF/DC-Locking.pdf
Could you explain what the above document is all about...
Robert.
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