[libcxx] r174642 - Belt and suspenders when calling sysconf

[Dave Zarzycki]

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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