4 Use of shared_ptr for asynchronous tasks

Christopher Kohlhoff tends to write classes that subclass std::enable_shared_from_this, for classes that manage the objects on which async operations can be posted (such as a socket or a deadline timer). When a lambda is created it holds a shared_ptr to the object, ensuring that the object is kept alive by the lambda.

For example:

class MyClass :  public std::enable_shared_from_this<MyClass>
{
    void do_async_thing()
    {
        auto self(shared_from_this());
        boost::asio::post(context_, 
            [this, self]() 
            {
                // do something
            });
    }

    boost::asio::io_context& context_;
}

We shall follow this design pattern, therefore object instances of the following classes shall be reference counted via shared_ptr:

• LazyFlusher
• LazyCheckPointer
• LazyCleaner
• LazyWriter
• CSpace
• TcpMsgServer
• TcpMsgClient
• TcpMsgSession

The LSS shall use shared_ptr as follows:

class LazyWriter
{
    std::shared_ptr<LazyFlusher> lazyFlusher_;
};

class SegmentWriter
{
    std::shared_ptr<LazyWriter> lazyWriter_;
};

class LSS
{
    SegmentWriter segmentWriter_;
    std::shared_ptr<LazyCleaner> lazyCleaner_;
    std::shared_ptr<LazyCheckPointer> lazyCheckPointer_;
};