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: Peter Dimov (lists_at_[hidden])
Date: 2015-01-20 19:07:53

Gaetano Mendola wrote:
> 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)
...

> 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 can't see anything wrong with your code; clang's thread sanitizer probably 
doesn't understand our homegrown atomic operations in 
sp_counted_base_gcc_x86.hpp because they use inline assembly.

You should try the same with -DBOOST_SP_USE_STD_ATOMIC, which will use 
std::atomic. It's possible that the sanitizer understands standard atomics 
better. Failing that, next thing to try is -DBOOST_SP_USE_PTHREADS.