Question

Here is a code below. The code is not complete, I omitted releasing resources part and implementation of QueryRes logic.

#define N 5

/*simply resources manager which has N shared resources*/
class ResourceManager
{
public:
    ResourceManager()
    {
            for (int i = 0; i < N; ++i)
              resources[i] = CreateMutex(NULL, FALSE, NULL);
    }
/*CreateMutex for on resources array in ctor*/
/*CloseHandle() in dtor and ReleaseMutex in another function which is called after QueryRes*/

        void QueryRes(int i)
        {
          WaitForSingleObject(resources[i], INFINITE); //(*) Here is the problem
        }

private:
        HANDLE resources[N];
};

/*User who asks for resource time-to-time*/
class User
{
public:
    User(ResourceManager& res_holder_, int res_num) : resource_holder(resource_holder), resource_to_query(res_num) {}

    void WorkWithResource()
    {
            while(1)
            {
                    resource_holder.QueryRes(resource_to_query);
            }
    }


    static void Run (void* params)
    {
            static_cast<User*>(params)->WorkWithResource();
    }

private:
    ResourceManager& resource_holder;
    int resource_to_query;
};

int main()
{
        ResourceManager resource_manager;
        User* users[5];
        HANDLE threads[5];

        for (size_t i = 0 ; i < 5; ++i)
        {
                users[i] = new User(resource_manager, i % 5);
                threads[i] = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)&User::Run, users[i], 0, NULL);
        }
        WaitForMultipleObjects(5, threads, true, INFINITE);


        return 0;
}

At (*) place I get an “access violation exception” when the function does WaitForSingleObject on already locked mutex.

I also tried

 while(WaitForSingleObject(resources[i], INFINITE) != WAIT_OBJECT_0) 

and got the same result.

Why do I get the exception?

I tried vc 2003, 2008 and 2010. I can’t use boost/pthreads/etc.

Thank you.

Answer 1

The error lies in the constructor of

User(ResourceManager& res_holder_, int res_num) : resource_holder(resource_holder), resource_to_query(res_num)    {   }

You should have

User(ResourceManager& res_holder_, int res_num) : resource_holder(**res_holder_**), resource_to_query(res_num)    {   }

instead !