Re: libm reentrancy

[Marcus Hult <marcushult at gmail dot com>]

Hello,

Thanks for your reply Gregory.

The sqrt function for instance, may set the errno variable according
to the manual. Shouldn’t this function then have a reentrant version?
Or do I always need to use the _impure_ptr when using libm, to be thread safe?

/Marcus

On Tue, Jan 8, 2013 at 2:45 PM, Gregory Pietsch <gpietsch@comcast.net> wrote:
> On 1/8/2013 6:36 AM, Marcus Hult wrote:
>>
>> Hello,
>>
>> I am a bit confused about reentrancy in the newlib libm. I have read
>> the explanation about the _REENT_ONLY flag here:
>> http://www.sourceware.org/ml/newlib/2003/msg00697.html.
>>
>> Most functions in libm does not have an _r version, but when defining
>> the symbol _REENT_ONLY, a lot of those functions are ifndef'ed out.
>> Why are there no reentrant versions of these functions? And how is the
>> _REENT_ONLY flag supposed to be used with libm?
>>
>> To make these functions in libm thread safe, i guess i need a _reent
>> struct in each thread and set the _impure_ptr to this when switching
>> tasks? Or how can i assure the libm function calls are thread safe?
>>
>> Thanks in advance
>>
> Most of the libm functions do not need to change any external state, so they
> should be thread-safe. The only ones I can think of that would be affected
> would be the functions in fenv.h because they rely on two external states.
> Any other comments?
>
> Gregory