Hi Matthias, Today Matthias Nagel wrote:
> Hi, > > > The setlocale() thread-safeness problems are well known, but there is also a > > rather significant lack of a decent widely adopted workaround. > > I know, but what I want to say is that according to this page [1] the > rrd_update_r function is said to be thread-save but it isn't. Hence, > if I had not stumbled across the first point (aka the memory bug) I > would not have noticed this one. I would never have assumed that > rrd_update_r uses setlocale. (Perhaps sometimes later in the future > after I would have observed strange behaviour.) That's why I asked for > a big warning at [1]. > > I do not know yet, if setlocale is the only problem with rrd_update_r, > but at least I see a bug fix for this one. There is no need to use > setlocale at all, if there was an interface like > > rrd_update_r( cont char* rrdFile, time_t ts, size_t argc, const char* > desc[], const T* val[] ) > > for T being a numeric type. This way one could avoid the conversion to > and from a string at all. The calling application is responsible of > providing the correct datatype. That should even simplify rrd_update_r > because there is no need to > parse an argument of the pattern "<ts>:<val 1>:...:<val n>". since all we are doing with setlocale in rrdtool, is to get strtod to be NOT locale sensitive. Another aproach would be to switch to a nonlocale sensitive implementation of strtod and get rid of all the setlocale calls. http://www.jbox.dk/sanos/source/lib/strtod.c.html care to provide a patch ? cheers tobi > Regards, Matthias > > [1] http://oss.oetiker.ch/rrdtool/prog/rrdthreads.en.html > > 2014-06-16 1:47 GMT+02:00 Donovan Baarda <[email protected]>: > > The setlocale() thread-safeness problems are well known, but there is also a > > rather significant lack of a decent widely adopted workaround. This is the > > problem with many of the standard C libraries... they pre-date threading, > > and there was never consensus/standardizing on any thread safe alternative. > > > > For any thread-safe alternative to work, everything needs to use it, but > > without a standard, you can pretty much guarantee that something you link > > will not use it, and some platforms won't even have it. > > > > So instead, your best option is often to just declare your code > > non-thread-safe and recommend subprocesses instead... but then the > > inter-process communication libs are not as well developed as the threading > > libs. > > > > Either that or completely embrace something like glib which replaces nearly > > everything in the standard C libs and only use other libs that also use > > glib. When you do this you also have to accept that your code doesn't look > > like normal C any more, and you might have some platform restrictions. > > > > > > > > On 16 June 2014 08:39, Matthias Nagel <[email protected]> wrote: > >> > >> Hello, > >> thanks. In the meantime I patched my Debian packages locally. But I ran > >> into another race condition. rrd_update_r() isn't thread-save, because the > >> C > >> locale is an application wide variable. Assume one has rrdlib (A) and some > >> other library (B) and the execution order is as follows: > >> > >> (A1) old_locale = setlocale(...) > >> (B1) old_locale = setlocale(...) > >> (A2) // do some locale-dependent stuff > >> (A3) setlocale( old_locale ) > >> (B2) // do some locale-dependent stuff > >> (B3) setlocale( old_locale ) > >> > >> Here, library B can be any library that also sets the global C locale > >> within a different thread context. In the best case some strings are > >> misinterpreted, in the worst case the memory gets corrupted :-( At the > >> moment, I wrote a work-around by using an application wide mutex that must > >> be locked by any thread that wants to call any library that might change > >> the > >> global C locale. But of course this isn't very nice. > >> > >> Are there any chances that the rrd_update_r function (and relatives) will > >> be rewritten? For example, C++ locales are bounded to a specific stream and > >> are not global. At least there should be big, BIG warning at > >> http://oss.oetiker.ch/rrdtool/prog/rrdthreads.en.html that the C locale is > >> subject to a race condition. > >> > >> Regards, Matthias > >> > >> Am Sonntag, 15. Juni 2014, 22:37:01 schrieb Tobias Oetiker: > >> > Hi Matthias, > >> > > >> > yes you are right ... we fixed this in master, but not in the 1.4 > >> > branch ... it is now ... > >> > > >> > cheers > >> > tobi > >> > > >> > Today Matthias Nagel wrote: > >> > > >> > > Hello, > >> > > > >> > > I am writing a multi-threaded C++ application that uses rrdlib > >> > > natively by calling rrd_update_r(). If I compile without > >> > > optimazations and > >> > > enable -ggdb everything seems to work fine. As soon as I switch to -O2 > >> > > and > >> > > disable -ggdb my apllication crashes at runtime. > >> > > > >> > > If it crashes the output is either > >> > > > >> > > *** glibc detected *** rrdtool: <something> > >> > > > >> > > or > >> > > > >> > > expected timestamp not found in data source from <input> > >> > > > >> > > but <input> is not the string that was given to rrd_update_r but > >> > > unreadable garbage. Obviously, it is a memory corruption problem. > >> > > Therefore, > >> > > I ran the application under valgrind and I noticed that the problems > >> > > comes > >> > > from inside of the rrdlib. The message is > >> > > > >> > > > >> > > ==11724== Invalid read of size 1 > >> > > ==11724== at 0x4C2A051: __GI_strcmp (mc_replace_strmem.c:712) > >> > > ==11724== by 0x5A4FF7F: setlocale (setlocale.c:210) > >> > > ==11724== by 0x505D06B: _rrd_update (rrd_update.c:982) > >> > > ==11724== Address 0x9deb0d0 is 0 bytes inside a block of size 12 > >> > > free'd > >> > > ==11724== at 0x4C27D4E: free (vg_replace_malloc.c:427) > >> > > ==11724== by 0x5A4FCBD: setname (setlocale.c:173) > >> > > ==11724== by 0x5A500B0: setlocale (setlocale.c:417) > >> > > ==11724== by 0x505D02D: _rrd_update (rrd_update.c:974) > >> > > > >> > > Let's have a look at it: > >> > > > >> > > rrd_update.c:973: old_locale = setlocale(LC_NUMERIC, NULL); > >> > > rrd_update.c:974: setlocale(LC_NUMERIC, "C"); > >> > > rrd_update.c:982: setlocale(LC_NUMERIC, old_locale); > >> > > > >> > > The problem is obvious. The variable "old_locale" that is used at the > >> > > 3rd line was assigned at the 1st line. But the 2nd call to "setlocale" > >> > > freed > >> > > the return value of the first call. According to the man pages the > >> > > return > >> > > value is a pointer to static memory and freed/allocated on every call. > >> > > Actually the 2nd line (974) should be ommited and it should be > >> > > > >> > > rrd_update.c:973: old_locale = setlocale(LC_NUMERIC, "C" ); > >> > > rrd_update.c:974: // deleted > >> > > rrd_update.c:982: setlocale(LC_NUMERIC, old_locale); > >> > > > >> > > Why this double call to "setlocale" anyway? > >> > > > >> > > Best regards, Matthias > >> > > > >> > > > >> > > >> > > >> > >> -- > >> Matthias Nagel > >> Parkstraße 27 > >> 76131 Karlsruhe > >> > >> Festnetz: +49-721-96869289 > >> Mobil: +49-151-15998774 > >> e-Mail: [email protected] > >> ICQ: 499797758 > >> Skype: nagmat84 > >> > >> _______________________________________________ > >> rrd-users mailing list > >> [email protected] > >> https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users > >> > > > > > > > > -- > > Donovan Baarda <[email protected]> > > > > -- Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland www.oetiker.ch [email protected] +41 62 775 9902
_______________________________________________ rrd-users mailing list [email protected] https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users
