Singleton initialization DCLP

[MikeWhy]

In context of the recent discussion of lazy initialization of singletons and
DCLP, is the behavior of the following safe, undefined, or unsafe?

class Foo {
....
protected:
Foo();
public:
static Foo & Instance()
{
static Foo singleton;
return singleton;
}
};

 

[Joshua Maurice]

In context of the recent discussion of lazy initialization of singletons and
DCLP, is the behavior of the following safe, undefined, or unsafe?

class Foo {
...
protected:
  Foo();
public:
  static Foo & Instance()
  {
     static Foo singleton;
     return singleton;
  }
};

For C++03 with POSIX pthreads and win32 threads implementations, this
lazy initialization is "not thread safe". Specifically, if the first
call to Instance() is not happens-before all other calls, aka if the
first calls are concurrent, then you have an effective race condition,
aka undefined behavior.