Re: [Rd] Fwd: [musl] strptime() question

[Rich Felker]

On Thu, Feb 04, 2016 at 04:35:22PM -0200, Alba Pompeo wrote:
> I forwarded our talk on musl mailing list to R mailing list.
> I got this response.
> Does it help?
> Also, what do you think about making a new email that's sent to both
> musl and R mailing list, that way devs from both projects can
> communicate? It's a tad inefficient for me to keep forwarding messages
> like this back and forth.

I'm cc'ing both lists now.

> -- Forwarded message --
> From: Simon Urbanek 
> Date: Thu, Feb 4, 2016 at 3:01 PM
> Subject: Re: [Rd] [musl] strptime() question
> To: Alba Pompeo 
> Cc: r-devel 
> 
> 
> 
> On Feb 4, 2016, at 11:20 AM, Alba Pompeo  wrote:
> 
> > There is incompatibility between R strptime and musl libc. I posted
> > about it on their mailing list, but they need more information I can't
> > provide, so I'm forwarding the message here in hope R developers can
> > help. Thanks.
> 
> Generally, it's using the standard tzset() call to set the time zone
> http://pubs.opengroup.org/onlinepubs/009695399/functions/tzset.html

The tzset function doesn't really do much interesting; it just updates
some global state to match the current value of the TZ environment
variable, but most time.h functions do this already anyway. Anyway
this doesn't really answer the question of what R's strptime function
is doing to add timezone functionality onto the underlying system's
strptime. Is R changing the environment (this is highly unsafe in any
potentially-multithreaded process, BTW)? Is it using the globals set
by tzset to compute adjustments to the result?

Rich

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Re: [Rd] [musl] Re: Fwd: [musl] strptime() question

[Rich Felker]

On Sat, Feb 06, 2016 at 10:35:28AM -0200, Alba Pompeo wrote:
> It is setting TZ and using tzset(). R is not multi-threaded so it is safe.
> 
> Simon figure out the important settings from the config.log and
> config.h files on a musl system:
> 
> /* #undef USE_INTERNAL_MKTIME */
> #define HAVE_TM_GMTOFF 1
> #define HAVE_TM_ZONE 1
> 
> Does this help anyone debug the issue? Simon just went on vacation.

R's src/main/datetime.c does A LOT of munging to the output of
strptime and I wouldn't be surprised if they're making nonportable
assumptions about it. Note that the underlying C strptime function has
nothing to do with timezones or time conversion; it's basically just a
time-tailored sscanf that reads integers and strings from the input
string and converts them into values in the fields of struct tm.

It also looks like R isn't even calling the system strptime but
instead using its own R_strptime. I think that supports my theory that
the problem is in the munging being done after the string is parsed.

Rich

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