What and When needs to be cleaned up when using msgpack-c?

Question

I am using Msgpack-c. One thing that is not clear to me, is how to correctly handle memory when using this library. The quickstart examples declare everything locally and I presume rely on destructors being called when the application ends, but I cannot rely on the same.

Take the following:

    msgpack::unpacked msgunpacked;
    msgpack::unpack(&msgunpacked, msgdata, msglength);
    T params = msgunpacked.get().as<T>();
    return params ;

When is it safe to delete msgdata? After unpack()? After the conversion to T?

When is it safe to delete msgunpacked? After get()?

Do I need to delete or free params? And do I need to destroy members like msgpack::type::raw_ref explicitly?

Answer 1

When is it safe to delete msgdata? After unpack()? After the conversion to T?

When you use msgpack::unpack() function, the default unpacking behavior is copy. So you can destroy msgdata after msgpack::unpack() is called.

See memory management

You can customize the behavior of copy. When you pass unpack_reference_func handler to msgpack::unpack(), and when the handler returns true, msgpack::unpacked might refer to msgdata. You can check the reference status via referenced parameter. If the reference parameter is set to true, the msgpack::unpacked refers to msgdata.

void unpack(
    object_handle& result,
    const char* data,
    std::size_t len,
    bool& referenced, // actual status for reference
    unpack_reference_func f = nullptr, // customize copy/reference behavior
    void* user_data = nullptr,
    unpack_limit const& limit = unpack_limit());

Strictly speaking, msgpack::unpacked doesn't refer to msgdata directly, msgpack::object that is held by msgpack::unpacked refers to msgdata.

When is it safe to delete msgunpacked? After get()?

See accessing unpacked data

get() is the member function for getting msgpack::object. The msgpack::object is located on msgpack::zone, a kind of memory pool. And msgpack::unpacked contains std::unique_ptr<msgpack::zone>. That means you need to keep the lifetime of msgunpacked during you access the msgpack::object that is gotten by get(). If you convert to T from msgpack::object, and the T doesn't refer to msgpack::object, and you don't access msgpack::object any more, then you can destroy msgunpacked. I said that the T doesn't refer to msgpack::object. It depends on the type of T. Most of the types do not refer to msgpack::object. msgpack::type::raw_ref, boost::string_ref, and msgpack::type::variant_ref refer to msgpack::object.

If you convert to those types, you need to keep the lifetime of msgpack::object.

See conversion , adaptor , variant_ref

Do I need to delete or free params?

No. T is located on the stack, you don't need to free it. If T contains the data on the heap like as std::vector<sometype>, the data should be freed by the destructor of the T.

And do I need to destroy members like msgpack::type::raw_ref explicitly?

No, you don't need to free msgpack::type::raw_ref. It is just a reference type object. The memory that is referred by msgpack::type::raw_ref is freed when msgunpacked is freed.