-mthreads on mingw 4.8.2 (on Fedora 20) now generating lihnking errors - should I use both -mthreads and -pthread?

Question

I just upgraded to Fedora 20 for a cross-compile project. Fedora 20 is using MinGW 4.8.2-1.fc20. My code is mostly there, but I am getting many undefined references to pthread_mutex_init and other pthread mutex functions on linking. I'm linking with the -mthreads option because my code is multi-threaded and uses exceptions.

The linking errors go away if I say -pthread. BUt that doesn't seem like the right think to do.

Here is a small test program:

#include <pthread.h>

int main(int argc,char **argv)
{
    pthread_mutex_t M;
    pthread_mutex_init(&M,0);
    exit(0);
}

Sample compile:

$ x86_64-w64-mingw32-g++ -mthreads x.cpp
/tmp/ccqTnLlg.o:x.cpp:(.text+0x21): undefined reference to `pthread_mutex_init'
collect2: error: ld returned 1 exit status
$

I can make it go away with:

$ x86_64-w64-mingw32-g++ -mthreads x.cpp -pthread
$

But that seems wrong.

For those not familiar with what -mthread is for, here is the section from the man page:

   -mthreads
       Support thread-safe exception handling on MinGW.  Programs that rely on thread-safe exception handling must compile and link all code with the
       -mthreads option.  When compiling, -mthreads defines "-D_MT"; when linking, it links in a special thread helper library -lmingwthrd which
       cleans up per-thread exception-handling data.

Any suggestions?

Answer 1

You're using pthreads, so use -pthreads. -mthreads is something else.