[cfe-dev] [libcxx] std::atomic default constructor

[Howard Hinnant]

I do not know if it will be in time or not for the next clang release.  I would be happy review such a patch.  I'd prefer a patch that switches on cxx_defaulted_functions, though I note that <atomic> doesn't compile at all in C++03 mode anyway.  So the only advantage would be that <atomic> might work on some hypothetical compiler that had cxx_atomic but not cxx_defaulted_functions.  I haven't investigated to know if this is a possibility.

Howard

On Apr 26, 2013, at 6:46 AM, Stephan Tolksdorf <st at quanttec.com> wrote:

> Hi Howard,
> 
> If I prepare a patch for the <atomic> header, can this still be fixed in time for the next Clang release? Or maybe you already have this on your todo list? It seems like a relatively ugly correctness issue that should be easy to fix.
> 
> Best regards,
>  Stephan
> 
> On 15.03.13, Howard Hinnant wrote:
>> Looks like a bug that needs fixing.  When I wrote <atomic>, = default wasn't implemented yet.  The entire library needs to be scanned for this issue.  And the fix needs to be macro'd up so that we don't break C++03 mode more than it already is.
>> 
>> Howard
>> 
>> On Mar 15, 2013, at 3:50 PM, Stephan Tolksdorf <st at quanttec.com> wrote:
>> 
>>> Hi,
>>> 
>>> Is there a reason that the default constructors for the std::atomic types in libc++'s <atomic> are not explicitly defaulted? In the header the "= default" is commented out and instead a trivial constructor is explicitly defined. This leads to non-standard behaviour, because value initialization doesn't zero-initialize the atomic value.
>>> 
>>> For example, the default constructor of the following struct Test does not zero-initialize atomicValue as expected:
>>> 
>>> struct Test {
>>>    int value{}; // is zero-initialized
>>>    std::atomic<int> atomicValue{}; // is not zero-initialized
>>> };
>>> 
>>> Best regards,
>>>  Stephan
>>> 
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>> 
>> 
> 
>