[Bug libstdc++/77704] Data race on std::ctype

[boris at kolpackov dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77704

--- Comment #5 from Boris Kolpackov <boris at kolpackov dot net> ---
For anyone interested, here is the workaround we came up with:

// A data race happens in the libstdc++ (as of GCC 7.2) implementation of the
// ctype<ctype>::narrow() function (bug #77704). The issue is easily triggered
// by the testscript runner that indirectly (via regex) uses ctype<char> facet
// of the global locale (and can potentially be triggered by other locale-
// aware code). We work around this by pre-initializing the global locale
// facet internal cache.
//
#ifdef _GLIBCXX_
  {
    const ctype<char>& ct (use_facet<ctype<char>> (locale ()));

    for (size_t i (0); i != 256; ++i)
      ct.narrow (static_cast<char> (i), '\0');
  }
#endif