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2bd9a072a9
- 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
64 lines
2.4 KiB
C++
64 lines
2.4 KiB
C++
/********************************************************************************
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* Copyright (C) 2026 GSI Helmholtzzentrum fuer Schwerionenforschung GmbH *
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* *
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* This software is distributed under the terms of the *
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* GNU Lesser General Public Licence (LGPL) version 3, *
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* copied verbatim in the file "LICENSE" *
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********************************************************************************/
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#ifndef FAIR_MQ_TEST_LOCALEWARMUP_H
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#define FAIR_MQ_TEST_LOCALEWARMUP_H
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#include <locale>
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#include <sstream>
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namespace fair::mq::test {
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/// libstdc++'s std::ctype<char> caches narrow()/widen() results per character
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/// in plain char arrays of the global classic-locale facet -- by design with
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/// unsynchronized writes, emitted from header-inlined code (locale_facets.h).
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/// Whenever two threads exercise an uncached character concurrently (e.g. by
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/// compiling a std::regex), ThreadSanitizer rightfully reports the write as a
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/// data race. The stores are real and unsynchronized, so instrumenting
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/// libstdc++ cannot help; instead, fill the caches before any thread exists,
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/// which turns every later access into a pure read.
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inline void WarmUpLocaleCaches()
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{
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auto const& ct = std::use_facet<std::ctype<char>>(std::locale::classic());
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for (int c = 1; c < 256; ++c) {
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auto const ch = static_cast<char>(c);
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ct.narrow(ch, '\0');
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ct.widen(ch);
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}
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// Only the range overload runs _M_narrow_init(), which sets the
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// all-cached flag (_M_narrow_ok); the single-char loop above fills the
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// cache without it. (widen() needs no equivalent: the single-char
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// overload already runs _M_widen_init().)
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char from[256];
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char to[256];
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for (int c = 0; c < 256; ++c) {
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from[c] = static_cast<char>(c);
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}
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ct.narrow(from, from + 256, '?', to);
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// num_put/num_get caches used by stream insertion/extraction
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std::ostringstream os;
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os << 4711 << ' ' << 3.14;
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std::istringstream is("42 3.14");
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int i = 0;
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double d = 0.;
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is >> i >> d;
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}
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/// For binaries that do not own main(): define a namespace-scope instance to
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/// run the warm-up during static initialization, before main().
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struct LocaleWarmup
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{
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LocaleWarmup() { WarmUpLocaleCaches(); }
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};
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} // namespace fair::mq::test
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#endif /* FAIR_MQ_TEST_LOCALEWARMUP_H */
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