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Subject: Re: [boost] [thread] Address sanitizer failures on marshall-mac
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2014-03-08 10:18:20

On Saturday 08 March 2014 14:25:45 Niall Douglas wrote:
> On 8 Mar 2014 at 0:55, Andrey Semashev wrote:
> > > The main cause of false positives is when Boost uses atomics to
> > > implement low level primitives such as locks. You need to annotate
> > > all CAS lock operations with the fact they are CAS locks - that way a
> > > thread sanitiser knows you're serialising code. Otherwise it appears
> > > you're riddling your code with race conditions.
> >
> > I think you're confusing ThreadSanitizer and AddressSanitizer. Double
> > free is never a false positive.
> No, but I think you didn't understand my post. Double frees which
> apparently occur Boost.Thread may in fact be double deletes in
> upstream code, so if type Foo's destructor has at some point the
> destruction of say a boost::future<>, double deleting Foo will appear
> as if Boost.Thread is double freeing. In fact the fault is in
> upstream code, not Boost.Thread.

That doesn't mean that the error is false positive. It just means that the
error is not in Boost.Thread.

I didn't say I'm 100% positive that the problem is in Boost.Thread. Although
I'd say this looks like the most probable case given that the problem is
indicated by multiple libraries, including Boost.Thread itself.

> > > Marking up all of Boost.Thread with all the necessary annotations and
> > > fixing up any problems revealed is probably a full (and extremely
> > > worthwhile) GSoC.
> >
> > I'd be careful with such markup. I don't know how exactly
> > ThreadSanitizer works, but if markup means calling some function in
> > runtime then that's probably not an acceptable solution in the context
> > of atomics.
> No functions are called in valgrind inserted markup. Just some
> harmless bytes which act as fingerprints. Normally the CPU skips
> right over them.

Even nop requires decoding effort, so it does have a cost. And I was referring
to ThreadSanitizer markup. Does it use the same markup as valgrind does?

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