Re: atomically thread-safe Meyers singleton impl (fixed)...

From:
Anthony Williams <anthony.ajw@gmail.com>
Newsgroups:
comp.lang.c++,comp.programming.threads
Date:
Wed, 30 Jul 2008 15:29:32 +0100
Message-ID:
<u8wvj4f8z.fsf@gmail.com>
"Chris M. Thomasson" <no@spam.invalid> writes:

"Anthony Williams" <anthony.ajw@gmail.com> wrote in message
news:uljzj4hf7.fsf@gmail.com...

"Dmitriy V'jukov" <dvyukov@gmail.com> writes:

On Jul 30, 8:44 am, "Chris Thomasson" <x...@xxx.xxx> wrote:

template<typename T>
struct singleton {
  static T* instance() {
    static T* volatile this_ptr = NULL;


I think here is a little problem. this_ptr is initialized dynamically,
and this initialization is not thread-safe. So some thread can
overwrite pointer in this_ptr with NULL.
You have to made this_ptr global, not function local, so it will be
initialized with NULL statically before any user code is executed.


Initialization with a constant is still static initialization, even
for function locals.


That's what I always thought. However, perhaps he is thinking along
the lines of:

struct foo {
 foo() {
   puts("HELLO!");
 }
};

void static_me_or_not(int flag) {
 if (flag == 666) {
   static foo x;
 }
}


Constructors are always dynamic initialization.

Anthony
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