[Bug libstdc++/42734] trivial use of std::thread fails with "pure virtual method called"

["damien.buhl at lecbna dot org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42734

--- Comment #46 from Damien Buhl (daminetreg) <damien.buhl at lecbna dot org> ---
As a pretier alternative you can use boost::thread with boost::atomic as
backend as we did in a yocto cross toolchain with the same issue where latomic
also segfaulted.

Cheers

fenixk19 at mail dot ru <gcc-bugzilla@gcc.gnu.org> a écrit :

>https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42734
>
>--- Comment #45 from Alexander Varnin <fenixk19 at mail dot ru> ---
>(In reply to Damien Buhl (daminetreg) from comment #44)
>
>While given test works properly with -latomic on my installation, my
>application doesn't. It fails with segfault in approximately half of launches.
>Core dump points to some thread execution code. I suppose, it is still broken
>in some way.
>
>Replacing std::thread in my code with pthread_* makes it work properly.
>
>So I conclude, that this std::thread and atomic things is broken on my gcc
>4.8.2 arm freescale imx53 yocto build.
>
>-- 
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Subject: A problem of template implicit instantiation
From: Yu Sheng Oh <humbleoh@gmail.com>
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HI,

I have a piece of code at "http://goo.gl/r2ySE6"

Refer to the code, with option of "-O2 -std=c++1y", when we comment
out the statement "id<int>;" clang-3.4.1 compiles the code
successfully, but g++-4.9.0 compiles failed, where g++ complains that
"unresolved overloaded function type", which in turn implies that at
the point of calling compose function, id<int> is not instantiated.

"3. Unless a function template specialization has been explicitly
instantiated or explicitly specialized, *the function template
specialization is implicitly instantiated  when the specialization is
referenced in a context that requires a function definition to exist.*
"[temp.inst]

At the point of calling the compose function, the function definition
for id<int> is required, and so, id<int> should be implicitly
instantiated.

Based on my argument, it is a bug in g++-4.9.0, but I am not 100% sure
of it. Please advice.

PS: Yongwei Wu is credited for discovering the problem.