Hi, > care to provide a patch ? I will see what I can do after I got my own application (the one that uses rrdlib) running. Matthias
2014-06-16 9:50 GMT+02:00 Tobias Oetiker <[email protected]>: > 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 -- 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
