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: Adam Romanek (romanek.adam_at_[hidden])
Date: 2014-07-01 03:12:50

On 30.06.2014 19:07, Niall Douglas wrote:
> 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.
>

The same happens with std::atomic from both libstdc++ [1] and libc++ [2] 
(I should be using pretty recent versions of these as I'm on Ubuntu 
14.04). So this is not a Boost-only issue.

>> 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

I'm not that worried. I just wanted to understand this situation and 
determine whether I need to correct my code somehow or I should just add 
a new suppression.

Thanks,

WBR,
Adam Romanek

[1] http://pastebin.com/56TLxpSR
[2] http://pastebin.com/STPbwbTS