Class to inform the
io_service when it has work to do.
Get the io_service associated with the work.
Constructor notifies the io_service that work is starting.
Copy constructor notifies the io_service that work is starting.
Destructor notifies the io_service that the work is complete.
The work class is used to inform the
io_service when work starts and
finishes. This ensures that the
will not exit while work is underway, and that it does exit when there is
no unfinished work remaining.
The work class is copy-constructible so that it may be used as a data member in a handler class. It is not assignable.