Re: [Boost-users] [atomic] ThreadSanitizer reports a data race when using the code from "reference counting" example

Subject: Re: [Boost-users] [atomic] ThreadSanitizer reports a data race when using the code from "reference counting" example
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2014-06-30 13:07:18

On 29 Jun 2014 at 21:16, Adam Romanek wrote:

> I'd like to draw your attention to an issue with Boost.Atomic that I 
> encountered when using ThreadSanitizer. The problem is that when using 
> the code shown in "reference counting" example [1] from the docs, the 
> ThreadSanitizer reports a data race. Everything is described in detail 
> in a StackOverflow thread [2] so I don't want to repeat all that here.
> 
> Please help me determine whether it's a false positive, an issue in 
> Boost.Atomic or a wrong usage of the code.

I'd try replacing boost::atomic with std::atomic and see if the same 
thing happens. Oh, and use a recent libstdc++. If it's only happening 
in Boost, report it as a bug.

> Additionally, I don't understand this:
> 
> Write of size 1 at 0x7d040000f7f0 by thread T2:
>      #0 operator delete(void*) <null>:0 (a.out+0x00000004738b)
> 
> What kind of write does ThreadSanitizer might refer to?

ThreadSanitiser tracks bounds of change, so if only one byte of 
change overlaps the raced bounds then it'll get reported as one byte.

tl;dr I wouldn't worry about it. ThreadSanitiser has many weirdness 
due to its design and straight out bugs. I am currently awaiting 
clang 3.5 release because 3.4 won't fully backtrace when libstdc++'s 
reference counted std::string has false positived a race, and I have 
dozens of workaround suppressions for it. Roll on libstdc++ 4.10 and 
its new std::string implementation!!!

Niall

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