std::lock_guard<std::mutex> segfaults on construction?

Question

I'm attempting to access a shared std::queue using a std::mutex and a std::lock_guard. The mutex (pending_md_mtx_) is a member variable of another object (whose address is valid). My code seems to be segfault'ing on the construction of the lock_guard.

Any ideas? Should I be using a std::unique_lock (or some other object) instead? Running GCC 4.6 (--std=c++0x) under Ubuntu Linux. I can't post the entire class, but the only accesses to the mutex and queue listed below.

template <typename ListenerT>
class Driver
{
public:
    template <typename... Args>
    Driver(Args&&... args) :
        listener_(std::forward<Args>(args)...) {}

    void enqueue_md(netw::Packet* packet)
    {
        std::lock_guard<std::mutex> lock(pending_md_mtx_);
        pending_md_.push(packet);
    }

    void process_md()
    {
        std::lock_guard<std::mutex> lock(pending_md_mtx_);
        while (pending_md_.size())
        {
            netw::Packet* pkt=pending_md_.front();
            pending_md_.pop();
            process_md(*pkt);
        }
    }
    //... Other code which I can't post...

private:
    ListenerT listener_;
    std::mutex pending_md_mtx_;
    std::queue<netw::Packet*> pending_md_;
};

GDB Stacktrace:

(gdb) bt
#0  __pthread_mutex_lock (mutex=0x2f20aa75e6f4000) at pthread_mutex_lock.c:50
#1  0x000000000041a2dc in __gthread_mutex_lock (__mutex=0xff282ceacb40) at /usr/include/c++/4.6/x86_64-linux-gnu/./bits/gthr-default.h:742
#2  lock (this=0xff282ceacb40) at /usr/include/c++/4.6/mutex:90
#3  lock_guard (__m=..., this=0x7f2874fc4db0) at /usr/include/c++/4.6/mutex:445
#4  driver::Driver<Listener, false>::enqueue_md (this=0xff282ceac8a0, packet=...) at exec/../../driver/Driver.hpp:95

Answer 1

I was getting a segfault on constructing the std::lock_guard, turns out my code was using an uninitialized std::shared_ptr<my_object_with_mutex>. Using a properly constructed my_object_with_mutex resolves the problem.