[libcxx] r174642 - Belt and suspenders when calling sysconf

[Marshall Clow]

On Feb 7, 2013, at 11:00 AM, Marshall Clow <mclow at qualcomm.com> wrote:

> 
> On Feb 7, 2013, at 10:54 AM, 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.
> 
> I understand, and this was not meant to be a general solution.
> 
> But, if by some weird circumstances we get handed a negative number of cores, we want to return a "not insane" value like 2^32-2.

Let me try that again - we want to NOT return an insane value like 2^32 -2.

The rationale behind this case was that we have to return a non-negative # - we can't just blindly pass back the return value from sysconf.

-- Marshall


>> 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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>>> cfe-commits at cs.uiuc.edu
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>> 
> 

-- Marshall

Marshall Clow     Idio Software   <mailto:mclow.lists at gmail.com>

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