[PATCH] Removing the static initializer in ManagedStatic.cpp by using llvm_call_once to initialize the ManagedStatic mutex.

[Chandler Carruth]

Can you instead use a windows specific api for implementing call once?
On Oct 30, 2014 12:09 PM, "Chris Bieneman" <beanz at apple.com> wrote:

> Ugh... So, std::atomic is off the table.
>
> I think we can do this instead:
>
> ```
> void llvm::call_once(once_flag &Initialized, void (*fptr)(void)) {
>   while (flag != Done) {
>     if (flag == Wait) {
>       ::Sleep(1);
>       continue;
>     }
>
>     sys::cas_flag old_val = sys::CompareAndSwap(&flag, Wait,
> Uninitialized);
>     if (old_val == Uninitialized) {
>       fptr();
>       sys::MemoryFence();
>       flag = Done;
>     }
>   }
>   sys::MemoryFence();
> }
>
> ```
> It ends up being a bit conservative on MemFences on x86, but it should be
> safe, and since once_flag is just an unsigned, it has a trivial static
> initializer and should avoid the issue that std::atomic has.
>
> http://reviews.llvm.org/D5922
>
>
>
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