[libcxx] r174642 - Belt and suspenders when calling sysconf

[Howard Hinnant]

Fwiw, Marshall discussed this change with me before committing.  That being said, I have no objection to reverting it either.  And either way we go, this code does not execute on Apple platforms (#ifdef'd out).

Howard

On Feb 7, 2013, at 1:54 PM, Dave Zarzycki <zarzycki at apple.com> wrote:

> Marshall,
> 
> FYI — While safe in this specific example, this is not a correct transform to make in the general case. POSIX very clearly specifies that -1 is the error code for this and similar APIs. This matters for APIs like mmap() which can return "negative" values that not an error.
> 
> davez
> 
> 
> On Feb 7, 2013, at 1:48 PM, Marshall Clow <mclow at qualcomm.com> wrote:
> 
>> Author: marshall
>> Date: Thu Feb  7 12:48:09 2013
>> New Revision: 174642
>> 
>> URL: http://llvm.org/viewvc/llvm-project?rev=174642&view=rev
>> Log:
>> Belt and suspenders when calling sysconf
>> 
>> Modified:
>>   libcxx/trunk/src/thread.cpp
>> 
>> Modified: libcxx/trunk/src/thread.cpp
>> URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/src/thread.cpp?rev=174642&r1=174641&r2=174642&view=diff
>> ==============================================================================
>> --- libcxx/trunk/src/thread.cpp (original)
>> +++ libcxx/trunk/src/thread.cpp Thu Feb  7 12:48:09 2013
>> @@ -69,7 +69,9 @@ thread::hardware_concurrency() _NOEXCEPT
>>    long result = sysconf(_SC_NPROCESSORS_ONLN);
>>    // sysconf returns -1 if the name is invalid, the option does not exist or
>>    // does not have a definite limit.
>> -    if (result == -1)
>> +    // if sysconf returns some other negative number, we have no idea
>> +    // what is going on. Default to something safe.
>> +    if (result < 0)
>>        return 0;
>>    return static_cast<unsigned>(result);
>> #else  // defined(CTL_HW) && defined(HW_NCPU)
>> 
>> 
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> 
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