Call a function before function exits

Question

I will begin with an example. Suppose I need to guard a code with a function inside a mutex. There are two ways of implementing this.

#include 
#         


        

Answer 1

What's wrong with writing your own generic resource wrapper?

template >
class resource_mgr
{
    Res* resource;
    Fn initialize, finalize;

public:
    resource_mgr (Res* r, Fn i, Fn f)
    : resource(r),
      initialize(i),
      finalize(f)
    {
        initialize(resource);
    }

    resource_mgr (resource_mgr const&) = delete;
    resource_mgr (resource_mgr&&)      = delete;

    resource_mgr const& operator = (resource_mgr const&) = delete;
    resource_mgr const& operator = (resource_mgr&&)      = delete;

    ~resource_mgr
    {
        try
        {
            finalize(resource);
        }
        catch(...)
        {
            std::cerr << "Uh-oh!"
        }
    }
};

You can keep it simple or go wild on something like this -- use smart pointers, define move operations, add support for custom error handlers, etc. You might use it like this:

void threadfunc_autolock(int i, float value)
{
    resource_mgr  autoMutex (
        &myMutex,
        [](auto* p) { if (!pthread_mutex_lock(p)) throw Something(); },
        [](auto* p) { if (!pthread_mutex_unlock(p)) throw Something(); }
    );

    /* . . . */
}