[boost] clang-3.6 thread sanitizer complains on shared_ptr operations

Subject: [boost] clang-3.6 thread sanitizer complains on shared_ptr operations
From: Gaetano Mendola (mendola_at_[hidden])
Date: 2015-01-20 18:50:08

I'm using clang 3.6 with boost 1.54

$ clang-3.6 --version
Ubuntu clang version 3.6.0-svn225356-1~exp1 (trunk) (based on LLVM 3.6.0)
Target: x86_64-pc-linux-gnu
Thread model: posix

Compiling the code here: http://pastebin.com/zh0SPz5n

$ clang++-3.6 -g main.cpp -lboost_system -lboost_thread -fsanitize=thread

I get at runtime:

==================
WARNING: ThreadSanitizer: data race (pid=5592)
  Write of size 8 at 0x7d080000cfe8 by thread T2 (mutexes: write M18):
    #0 operator delete(void*) <null> (a.out+0x00000045febb)
    #1 ~sp_counted_impl_p /usr/include/boost/smart_ptr/detail/sp_counted_impl.hpp:53 (a.out+0x0000004d15c9)
    #2 boost::detail::sp_counted_base::destroy() /usr/include/boost/smart_ptr/detail/sp_counted_base_gcc_x86.hpp:126 (a.out+0x0000004cb77c)
    #3 boost::detail::sp_counted_base::weak_release() /usr/include/boost/smart_ptr/detail/sp_counted_base_gcc_x86.hpp:160 (a.out+0x0000004c773f)
    #4 boost::detail::sp_counted_base::release() /usr/include/boost/smart_ptr/detail/sp_counted_base_gcc_x86.hpp:147 (a.out+0x0000004c75e8)
    #5 ~shared_count /usr/include/boost/smart_ptr/detail/shared_count.hpp:371 (a.out+0x0000004c7550)
    #6 ~shared_ptr /usr/include/boost/smart_ptr/shared_ptr.hpp:722 (a.out+0x0000004cef59)
    #7 boost::shared_ptr<int>::operator=(boost::shared_ptr<int> const&) /usr/include/boost/smart_ptr/shared_ptr.hpp:507 (a.out+0x0000004cf1b7)
    #8 Consumer::consume(boost::shared_ptr<int>) /home/kalman/boost_sp_test/main.cpp:9 (a.out+0x0000004ced61)
    #9 Producer::operator()() /home/kalman/boost_sp_test/main.cpp:32 (a.out+0x0000004ceaba)
    #10 boost::detail::thread_data<boost::reference_wrapper<Producer> >::run() /usr/include/boost/thread/detail/thread.hpp:137 (a.out+0x0000004cc29e)
    #11 boost::this_thread::interruption_requested() <null> (libboost_thread.so.1.54.0+0x00000000ba49)

  Previous read of size 4 at 0x7d080000cfe8 by thread T1:
    #0 boost::detail::sp_counted_base::use_count() const /usr/include/boost/smart_ptr/detail/sp_counted_base_gcc_x86.hpp:166 (a.out+0x0000004cb33e)
    #1 boost::detail::shared_count::use_count() const /usr/include/boost/smart_ptr/detail/shared_count.hpp:423 (a.out+0x0000004cf040)
    #2 boost::shared_ptr<int>::use_count() const /usr/include/boost/smart_ptr/shared_ptr.hpp:681 (a.out+0x0000004cefb9)
    #3 Consumer::operator()() /home/kalman/boost_sp_test/main.cpp:19 (a.out+0x0000004d4a29)
    #4 boost::detail::thread_data<boost::reference_wrapper<Consumer> >::run() /usr/include/boost/thread/detail/thread.hpp:137 (a.out+0x0000004d497e)
    #5 boost::this_thread::interruption_requested() <null> (libboost_thread.so.1.54.0+0x00000000ba49)

  Mutex M18 (0x7fff01719338) created at:
    #0 pthread_mutex_init <null> (a.out+0x0000004641e0)
    #1 mutex /usr/include/boost/thread/pthread/mutex.hpp:100 (a.out+0x0000004d1867)
    #2 Consumer /home/kalman/boost_sp_test/main.cpp:5 (a.out+0x0000004c6238)
    #3 main /home/kalman/boost_sp_test/main.cpp:41 (a.out+0x0000004c5903)

  Thread T2 (tid=5595, running) created by main thread at:
    #0 pthread_create <null> (a.out+0x000000462db1)
    #1 boost::thread::start_thread_noexcept() <null> (libboost_thread.so.1.54.0+0x00000000b3b8)
    #2 thread<boost::reference_wrapper<Producer> > /usr/include/boost/thread/detail/thread.hpp:302 (a.out+0x0000004c6639)
    #3 main /home/kalman/boost_sp_test/main.cpp:45 (a.out+0x0000004c59bd)

  Thread T1 (tid=5594, running) created by main thread at:
    #0 pthread_create <null> (a.out+0x000000462db1)
    #1 boost::thread::start_thread_noexcept() <null> (libboost_thread.so.1.54.0+0x00000000b3b8)
    #2 thread<boost::reference_wrapper<Consumer> > /usr/include/boost/thread/detail/thread.hpp:302 (a.out+0x0000004c6479)
    #3 main /home/kalman/boost_sp_test/main.cpp:44 (a.out+0x0000004c5968)

SUMMARY: ThreadSanitizer: data race ??:0 operator delete(void*)
==================

I believe this is a false alarm indeed the two threads are working on their own shared_ptr copy and thePtr shared pointer
write/read in the two threads is protected with a mutex.

I will open a ticket with clang folks if you recognize that is a false alarm, unless they are right and we have issue in 
shared_ptr implementation.

Regards
Gaetano

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