Re: singleton - dead reference
On 14 nov, 08:44, Hoobert <michal...@yahoo.pl> wrote:
Hello,
While reading "Implementing Singletons" in "Modern C++ Design" by A.
Alexandrescu I bumped into example:
//-----------------------------------------------
class Singleton {
public:
static Singleton& Instance() {
if (!pInstance_) {
if (destroyed_) OnDeadReference();
else Create();
}
return *pInstance_;
}
private:
static void Create() {
static Singleton instance;
pInstance_=&instance;
}
static void OnDeadReference() {
Create();
new(pInstance_) Singleton;
atexit(KillPhoenix);
destroyed_=false;
}
static void KillPhoenix() {
pInstance_->~Singleton();
}
virtual ~Singleton() {
pInstance_=0;
destroyed_=true;
}
static Singleton *pInstance_;
static bool destroyed_;};
//-----------------------------------------------
which addresses problem of dead references due to order of static
objects' destruction. I don't get the OnDeadReference function:
why there is "new(pInstance_) Singleton;" ?
That's placement new.
It calls the constructor. Of course it is only allowed to do that
after the destuctor has been called, which is done in KillPhoenix.
Basically, it's a singleton you can kill and resurrect.
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