llvm dev - Mar 2015 - [LLVMdev] multithreading and the JIT, specifically llvm::sys::Memory

Hello,
We were doing some experiments to deserialize/JIT bitcode on multiple threads
and we hit what looks like this issue:
http://lists.cs.uiuc.edu/pipermail/llvmbugs/2013-April/027937.html

We're using LLVM-3.5 so I was a bit surprised that the patch that was
provided in 2013 doesn't appear to be in the current codebase. I'm
curious what the status of this patch and issue are? Are other people
multithreading their code this way?

Thanks!
  Dale

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Dale Martin <Dale.Martin at mathworks.com> writes:
> We were doing some experiments to deserialize/JIT bitcode on multiple
threads
> and we hit what looks like this issue:
>
> http://lists.cs.uiuc.edu/pipermail/llvmbugs/2013-April/027937.html
>
> We’re using LLVM-3.5 so I was a bit surprised that the patch that was
provided
> in 2013 doesn’t appear to be in the current codebase. I’m curious what the
> status of this patch and issue are? Are other people multithreading their
code
> this way?
I didn't look into it, but the bug's description states this only
happens when LLVM is built by a pre-C++11 compiler. Trunk requires C++11
these days, so is this fix even relevant anymore?

> I didn't look into it, but the bug's description states this only
happens when LLVM is built by a pre-C++11 compiler. Trunk requires C++11 these
days, so is this fix even relevant anymore?
We're seeing this bug on win64, where we're building with Visual 2012. 
I don't know if you'd count it as a pre-C++11 compiler or not, or for
that matter, how one would count Visual 2013, which is more C++-11 compliant but
still incomplete in its support.  We're considering if it is worth
investigating locally applying the patch or if this is just the tip of the
iceberg.

Thanks,
  Dale

On Mon, Mar 23, 2015 at 11:51 AM, Justin Bogner <mail at justinbogner.com>
wrote:
> Dale Martin <Dale.Martin at mathworks.com> writes:
> > We were doing some experiments to deserialize/JIT bitcode on multiple
> threads
> > and we hit what looks like this issue:
> >
> > http://lists.cs.uiuc.edu/pipermail/llvmbugs/2013-April/027937.html
> >
> > We’re using LLVM-3.5 so I was a bit surprised that the patch that was
> provided
> > in 2013 doesn’t appear to be in the current codebase. I’m curious what
> the
> > status of this patch and issue are? Are other people multithreading
> their code
> > this way?
>
> I didn't look into it, but the bug's description states this only
> happens when LLVM is built by a pre-C++11 compiler. Trunk requires C++11
> these days, so is this fix even relevant anymore?
>
It's still relevant. Our minimum supported VS version is 2013, which
doesn't have thread safe statics yet. VS 2015 will have it, but it
hasn't
been officially released yet. Six CTPs and still going strong. :)

Probably the best thing to do here is some manual atomic checking and
setting of the page size. ManagedStatic is IMO too heavyweight.
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