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

Subject: Re: [boost] clang-3.6 thread sanitizer complains on shared_ptr operations
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2015-01-21 01:37:17

On Wed, Jan 21, 2015 at 8:57 AM, Vicente J. Botet Escriba
<vicente.botet_at_[hidden]> wrote:
> Le 21/01/15 00:50, Gaetano Mendola a écrit :
>>
>> 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)
>> <snip>
>> 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.
>>
>>
> Thanks for raising this issue. The Boost.Thread regression tests are showing
> this kind of issues since the testers were installed by Marshall.
>
> Your example seems to show that the issue is only related to
> boost::shared_ptr. In order we can concentrate only on Boost::SmartPtr,
> could you give a try replacing Boost.Thread by
> (std::thread/mutex/unique_lock)?

This is not specific to Boost.SmartPtr. Any library that implements
atomics, including Boost.Atomic and std::atomic, will likely be
present in TSan reports. The problem is that TSan does not fully
support C++ memory ordering arguments. See this thread:

http://boost.2283326.n4.nabble.com/atomic-ThreadSanitizer-reports-a-data-race-when-using-the-code-from-quot-reference-counting-quot-exae-td4664533.html