std thread,mutex,cv and static linking with GCC

[Jonathan Wakely]

On 22 October 2014 16:40, Damian Lezama wrote:
> Hi,
>
> I was getting random crashes when using thread, mutex, and cv and statically linking my project. Some of the libraries I link against use pthread, so I narrowed the issue down to this test:
>
> I statically link a simple test that uses thread, mutex, and cv like this: "g++ --std=c++11 -pthread -static test.cc" and  I get this when I run it:
>
> terminate called after throwing an instance of 'std::system_error'
>   what():  Enable multithreading to use std::thread: Operation not permitted
> Aborted
>
> Everything works fine if I don't use -static, the problem is specific to static linking. If in my test I use pthread directly to create a thread, then it runs and creating an std::thread also works, but the test crashes when using the cv. My theory is that the linker is being lazy (weak references? optimization?) and the pthread stuff std needs is not included in the binary unless referenced somewhere else. In real projects this is quite dangerous because having dependencies that use most of the pthread stuff makes these crashes rare (I caught this problem with a stress test).
>
> Any ideas? Is this s bug in the library?

Yes, your theory is basically correct.

Some GNU/Linux distributions (at least Fedora and Red Hat and its
clones) have some custom modifications to libpthread.a that ensures
linking statically works. I don't remember the details.

An alternative that might help is to use something like
-Wl,--whole-archive -lpthread -Wl,--no-whole-archive to link in
everything from libpthread.

Finally, I believe the problem is solved in the current GCC trunk (at
least on GNU/Linux) by a change I made to std::thread that adds an
explicit dependency on pthread_create, which should force libpthread
to be linked to. I think that might have been backported to the Debian
and/or Ubuntu packages for GCC 4.8 and 4.9.