Possible data race in src/pthread/once_atomic.cpp

Start with src/pthread/once_atomic.cpp and reproduce the Helgrind report using util_ipc_reliable_mq.cpp from boostorg/log. Compare the reported reads and writes in once_atomic.cpp with the related call paths in the stack trace and issue 162. Done means the suspected race is resolved and the test no longer reports these conflicts under Helgrind.

Possible data race is found when running test util_ipc_reliable_mq.cpp in boostorg/log. See https://github.com/boostorg/log/issues/162 for more details.
Valgrind shows the following errors for this test:

# Run command: valgrind --tool=helgrind binary_path
==537225== Possible data race during read of size 4 at 0x4FE76B8 by thread #3
==537225== Locks held: none
==537225==    at 0x4FD453C: load (core_ops_gcc_atomic.hpp:88)
==537225==    by 0x4FD453C: load (atomic_impl.hpp:338)
==537225==    by 0x4FD453C: boost::thread_detail::enter_once_region(boost::once_flag&) (once_atomic.cpp:39)
==537225==    by 0x4FBFED8: void boost::call_once<void (&)()>(boost::once_flag&, void (&)()) (once_atomic.hpp:123)
==537225==    by 0x4FBD17E: boost::detail::set_current_thread_data(boost::detail::thread_data_base*) (thread.cpp:160)
==537225==    by 0x4FBD346: boost::(anonymous namespace)::thread_proxy(void*) (thread.cpp:174)
==537225==    by 0x4C37EEE: mythread_wrapper (hg_intercepts.c:387)
==537225==    by 0x5E4D2DD: start_thread (in /usr/lib64/libpthread-2.28.so)
==537225==    by 0x6160E82: clone (in /usr/lib64/libc-2.28.so)
==537225==
==537225== This conflicts with a previous write of size 4 by thread #2
==537225== Locks held: 1, at address 0x4FE77B0
==537225==    at 0x4FD53F5: store (core_ops_gcc_atomic.hpp:76)
==537225==    by 0x4FD53F5: store (atomic_impl.hpp:330)
==537225==    by 0x4FD53F5: boost::thread_detail::commit_once_region(boost::once_flag&) (once_atomic.cpp:74)
==537225==    by 0x4FBFF66: void boost::call_once<void (&)()>(boost::once_flag&, void (&)()) (once_atomic.hpp:138)
==537225==    by 0x4FBD17E: boost::detail::set_current_thread_data(boost::detail::thread_data_base*) (thread.cpp:160)
==537225==    by 0x4FBD346: boost::(anonymous namespace)::thread_proxy(void*) (thread.cpp:174)
==537225==    by 0x4C37EEE: mythread_wrapper (hg_intercepts.c:387)
==537225==    by 0x5E4D2DD: start_thread (in /usr/lib64/libpthread-2.28.so)
==537225==    by 0x6160E82: clone (in /usr/lib64/libc-2.28.so)
==537225==  Address 0x4fe76b8 is 0 bytes inside data symbol "_ZN5boost6detail12_GLOBAL__N_128current_thread_tls_init_flagE"
==537225==
==537225== ----------------------------------------------------------------
==537225==
==537225== Possible data race during read of size 4 at 0x4FE76BC by thread #3
==537225== Locks held: none
==537225==    at 0x4FBD17F: boost::detail::set_current_thread_data(boost::detail::thread_data_base*) (thread.cpp:161)
==537225==    by 0x4FBD346: boost::(anonymous namespace)::thread_proxy(void*) (thread.cpp:174)
==537225==    by 0x4C37EEE: mythread_wrapper (hg_intercepts.c:387)
==537225==    by 0x5E4D2DD: start_thread (in /usr/lib64/libpthread-2.28.so)
==537225==    by 0x6160E82: clone (in /usr/lib64/libc-2.28.so)
==537225==
==537225== This conflicts with a previous write of size 4 by thread #2
==537225== Locks held: none
==537225==    at 0x5E5476F: pthread_key_create (in /usr/lib64/libpthread-2.28.so)
==537225==    by 0x4FC9F36: _ZN5boost6detail6invokeIPFvvEJEEEDTclclsr5boostE7forwardIT_Efp_Espclsr5boostE7forwardIT0_Efp0_EEEOS4_DpOS5_ (invoke.hpp:133)
==537225==    by 0x4FBFF10: void boost::call_once<void (&)()>(boost::once_flag&, void (&)()) (once_atomic.hpp:127)
==537225==    by 0x4FBD17E: boost::detail::set_current_thread_data(boost::detail::thread_data_base*) (thread.cpp:160)
==537225==    by 0x4FBD346: boost::(anonymous namespace)::thread_proxy(void*) (thread.cpp:174)
==537225==    by 0x4C37EEE: mythread_wrapper (hg_intercepts.c:387)
==537225==    by 0x5E4D2DD: start_thread (in /usr/lib64/libpthread-2.28.so)
==537225==    by 0x6160E82: clone (in /usr/lib64/libc-2.28.so)
==537225==  Address 0x4fe76bc is 0 bytes inside data symbol "_ZN5boost6detail12_GLOBAL__N_122current_thread_tls_keyE"