- std::ctype<char> caches narrow()/widen() results per character in
plain char arrays of the global classic-locale facet, written without
synchronization from header-inlined code (locale_facets.h); two
threads exercising an uncached character concurrently (e.g. compiling
a std::regex in Channel::Validate) constitute a true data race that
ThreadSanitizer rightfully reports
- the stores are real and unsynchronized, so a tsan-instrumented
libstdc++ cannot help here; instead fill the caches before any thread
is spawned, which turns every later access into a pure read
- warm the lazily-installed num_put/num_get caches used by stream
insertion/extraction as well, via a small format/parse round-trip
- wire the warm-up into the gtest runner main() and, via a static
initializer, into the test device runner
