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

[morandidodo at gmail dot com]

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

            Bug ID: 77704
           Summary: Data race on std::regex
           Product: gcc
           Version: 6.2.1
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: morandidodo at gmail dot com
  Target Milestone: ---

The thread sanitizer says that there is a data race during regex construction.
Here a simple test:

#include <regex>
#include <string>
#include <thread>

static const std::string test_string =
"aiusndougbafiudboihvboauvhbadnofhdbvouahvebfdocsahkbnavoiekrhfdsbvjqon";
static constexpr unsigned n_threads = 30;

void test()
{
    std::regex re = std::regex("[abg][jtd]");
    std::regex_match(test_string, re);
}

int main()
{
    std::vector<std::thread> threads;
    threads.reserve(n_threads);
    for(unsigned i = 0; i < n_threads; ++i)
        threads.emplace_back(test);

    for(unsigned i = 0; i < n_threads; ++i)
        threads[i].join();
}


Compiled with GCC 6.2.1, using
g++ -Wall -Wextra -O3 test.cpp -o test -g -pthread -fsanitize=thread

Running the test gives these "results":
==================
WARNING: ThreadSanitizer: data race (pid=14501)
  Read of size 1 at 0x7fc2e581b1f4 by thread T2:
    #0 std::ctype<char>::narrow(char, char) const
/usr/include/c++/6.2.1/bits/locale_facets.h:932 (test+0x0000004064f4)
    #1 std::__detail::_Scanner<char>::_M_scan_normal()
/usr/include/c++/6.2.1/bits/regex_scanner.tcc:101 (test+0x0000004064f4)
    #2 std::__detail::_Scanner<char>::_M_advance()
/usr/include/c++/6.2.1/bits/regex_scanner.tcc:80 (test+0x0000004083af)
    #3 std::__detail::_Scanner<char>::_Scanner(char const*, char const*,
std::regex_constants::syntax_option_type, std::locale)
/usr/include/c++/6.2.1/bits/regex_scanner.tcc:66 (test+0x0000004083af)
    #4 std::__detail::_Compiler<std::__cxx11::regex_traits<char>
>::_Compiler(char const*, char const*, std::locale const&,
std::regex_constants::syntax_option_type)
/usr/include/c++/6.2.1/bits/regex_compiler.tcc:78 (test+0x000000422b8a)
    #5 std::enable_if<std::__detail::__is_contiguous_normal_iter<char
const*>::value,
std::shared_ptr<std::__detail::_NFA<std::__cxx11::regex_traits<char> > const>
>::type std::__detail::__compile_nfa<char const*,
std::__cxx11::regex_traits<char> >(char const*, char const*,
std::__cxx11::regex_traits<char>::locale_type const&,
std::regex_constants::syntax_option_type)
/usr/include/c++/6.2.1/bits/regex_compiler.h:194 (test+0x00000042379f)
    #6 std::__cxx11::basic_regex<char, std::__cxx11::regex_traits<char>
>::basic_regex<char const*>(char const*, char const*, std::locale,
std::regex_constants::syntax_option_type)
/usr/include/c++/6.2.1/bits/regex.h:767 (test+0x0000004034df)
    #7 std::__cxx11::basic_regex<char, std::__cxx11::regex_traits<char>
>::basic_regex<char const*>(char const*, char const*,
std::regex_constants::syntax_option_type)
/usr/include/c++/6.2.1/bits/regex.h:512 (test+0x0000004034df)
    #8 std::__cxx11::basic_regex<char, std::__cxx11::regex_traits<char>
>::basic_regex(char const*, std::regex_constants::syntax_option_type)
/usr/include/c++/6.2.1/bits/regex.h:445 (test+0x0000004034df)
    #9 test() /tmp/test3.cpp:10 (test+0x0000004034df)
    #10 void std::_Bind_simple<void (*())()>::_M_invoke<>(std::_Index_tuple<>)
/usr/include/c++/6.2.1/functional:1400 (test+0x000000403fc9)
    #11 std::_Bind_simple<void (*())()>::operator()()
/usr/include/c++/6.2.1/functional:1389 (test+0x000000403fc9)
    #12 std::thread::_State_impl<std::_Bind_simple<void (*())()> >::_M_run()
/usr/include/c++/6.2.1/thread:196 (test+0x000000403fc9)
    #13 execute_native_thread_routine
/build/gcc-multilib/src/gcc/libstdc++-v3/src/c++11/thread.cc:83
(libstdc++.so.6+0x0000000bb31e)

  Previous write of size 1 at 0x7fc2e581b1f4 by thread T1:
    #0 std::ctype<char>::narrow(char, char) const
/usr/include/c++/6.2.1/bits/locale_facets.h:936 (test+0x00000040665d)
    #1 std::__detail::_Scanner<char>::_M_scan_normal()
/usr/include/c++/6.2.1/bits/regex_scanner.tcc:101 (test+0x00000040665d)
    #2 std::__detail::_Scanner<char>::_M_advance()
/usr/include/c++/6.2.1/bits/regex_scanner.tcc:80 (test+0x0000004083af)
    #3 std::__detail::_Scanner<char>::_Scanner(char const*, char const*,
std::regex_constants::syntax_option_type, std::locale)
/usr/include/c++/6.2.1/bits/regex_scanner.tcc:66 (test+0x0000004083af)
    #4 std::__detail::_Compiler<std::__cxx11::regex_traits<char>
>::_Compiler(char const*, char const*, std::locale const&,
std::regex_constants::syntax_option_type)
/usr/include/c++/6.2.1/bits/regex_compiler.tcc:78 (test+0x000000422b8a)
    #5 std::enable_if<std::__detail::__is_contiguous_normal_iter<char
const*>::value,
std::shared_ptr<std::__detail::_NFA<std::__cxx11::regex_traits<char> > const>
>::type std::__detail::__compile_nfa<char const*,
std::__cxx11::regex_traits<char> >(char const*, char const*,
std::__cxx11::regex_traits<char>::locale_type const&,
std::regex_constants::syntax_option_type)
/usr/include/c++/6.2.1/bits/regex_compiler.h:194 (test+0x00000042379f)
    #6 std::__cxx11::basic_regex<char, std::__cxx11::regex_traits<char>
>::basic_regex<char const*>(char const*, char const*, std::locale,
std::regex_constants::syntax_option_type)
/usr/include/c++/6.2.1/bits/regex.h:767 (test+0x0000004034df)
    #7 std::__cxx11::basic_regex<char, std::__cxx11::regex_traits<char>
>::basic_regex<char const*>(char const*, char const*,
std::regex_constants::syntax_option_type)
/usr/include/c++/6.2.1/bits/regex.h:512 (test+0x0000004034df)
    #8 std::__cxx11::basic_regex<char, std::__cxx11::regex_traits<char>
>::basic_regex(char const*, std::regex_constants::syntax_option_type)
/usr/include/c++/6.2.1/bits/regex.h:445 (test+0x0000004034df)
    #9 test() /tmp/test3.cpp:10 (test+0x0000004034df)
    #10 void std::_Bind_simple<void (*())()>::_M_invoke<>(std::_Index_tuple<>)
/usr/include/c++/6.2.1/functional:1400 (test+0x000000403fc9)
    #11 std::_Bind_simple<void (*())()>::operator()()
/usr/include/c++/6.2.1/functional:1389 (test+0x000000403fc9)
    #12 std::thread::_State_impl<std::_Bind_simple<void (*())()> >::_M_run()
/usr/include/c++/6.2.1/thread:196 (test+0x000000403fc9)
    #13 execute_native_thread_routine
/build/gcc-multilib/src/gcc/libstdc++-v3/src/c++11/thread.cc:83
(libstdc++.so.6+0x0000000bb31e)

  Location is global '(anonymous namespace)::ctype_c' of size 576 at
0x7fc2e581b060 (libstdc++.so.6+0x0000003861f4)

  Thread T2 (tid=14504, running) created by main thread at:
    #0 pthread_create
/build/gcc-multilib/src/gcc/libsanitizer/tsan/tsan_interceptors.cc:876
(libtsan.so.0+0x000000028470)
    #1 __gthread_create
/build/gcc-multilib/src/gcc-build/x86_64-pc-linux-gnu/libstdc++-v3/include/x86_64-pc-linux-gnu/bits/gthr-default.h:662
(libstdc++.so.6+0x0000000bb634)
    #2 std::thread::_M_start_thread(std::unique_ptr<std::thread::_State,
std::default_delete<std::thread::_State> >, void (*)())
/build/gcc-multilib/src/gcc/libstdc++-v3/src/c++11/thread.cc:163
(libstdc++.so.6+0x0000000bb634)
    #3 __libc_start_main <null> (libc.so.6+0x000000020290)

  Thread T1 (tid=14503, running) created by main thread at:
    #0 pthread_create
/build/gcc-multilib/src/gcc/libsanitizer/tsan/tsan_interceptors.cc:876
(libtsan.so.0+0x000000028470)
    #1 __gthread_create
/build/gcc-multilib/src/gcc-build/x86_64-pc-linux-gnu/libstdc++-v3/include/x86_64-pc-linux-gnu/bits/gthr-default.h:662
(libstdc++.so.6+0x0000000bb634)
    #2 std::thread::_M_start_thread(std::unique_ptr<std::thread::_State,
std::default_delete<std::thread::_State> >, void (*)())
/build/gcc-multilib/src/gcc/libstdc++-v3/src/c++11/thread.cc:163
(libstdc++.so.6+0x0000000bb634)
    #3 __libc_start_main <null> (libc.so.6+0x000000020290)

SUMMARY: ThreadSanitizer: data race
/usr/include/c++/6.2.1/bits/locale_facets.h:932 in
std::ctype<char>::narrow(char, char) const
==================
ThreadSanitizer: reported 1 warnings