io_service to invoke the given
template< typename Function, typename Allocator> void defer( Function && f, const Allocator & a);
If the current thread belongs to the
defer() will delay scheduling the function object
until the current thread returns control to the pool.
The function object to be called. The executor will make a copy of the handler object as required. The function signature of the function object must be:
An allocator that may be used by the executor to allocate the internal storage needed for function invocation.