Is it safe to mix pthread.h and C++11 standard library threading features?

Question

Can I spawn a thread with pthread_create and use std::mutex inside of it safely?

I would think that if std::mutex is implemented as a pthread_mutex_t then it would be fine but I don't see this documented anywhere

For example:

#include <pthread.h>
#include <mutex>

namespace {
std::mutex global_lock;
}

void* thread_func(void* vp) {
    // std::mutex used in thread spawned with pthread_create
    std::lock_guard<std::mutex> guard(global_lock);
    // critical section
    return nullptr;
}

int main() {
    pthread_t tid;
    pthread_create(&tid, nullptr, thread_func, nullptr);
    pthread_join(tid, NULL);
}

BTW I'm running Debian Wheezy.

Answer 1

You could on my machine (Debian too). But I'm not sure if I would call this safe.

If you look at the relevant file, /usr/include/c++/4.7/i486-linux-gnu/bits/gthr-default.h in my case, you will see that there will be a 1:1 mapping to the pthreads api. <mutex> uses __gthread_mutex_lock for locking which is defined exactly there to pthread_mutex_lock. Or you will see that std::thread declares typedef __gthread_t native_handle_type;

I don't know if there is a documented way to check if pthreads are used. But gthr-default.h defines _GLIBCXX_GCC_GTHR_POSIX_H as include guard and I think as long as this macro is defined, you can assume that you can mix them both.

Edit: Given the hint from @Wakely, I would write:

template <typename T>
using strip = typename std::remove_pointer<typename std::decay<T>::type>::type;

static_assert(std::is_same<strip<std::thread::native_handle_type>, pthread_t>::value,
              "libstdc++ doesn't use pthread_t");