template< typename Function, typename Allocator> void defer( Function && f, const Allocator & a);
This function is used to ask the thread pool to execute the given function
object. The function object will never be executed inside
Instead, it will be scheduled to run on the thread pool.
If the current thread belongs to the thread pool,
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.