What is a runtime engine?

A runtime engine of WF gives the basic functionality to execute and manage the workflow lifetime. It runs within the host process and is responsible for implementing each workflow instance. A host process can interact with multiple runtime engines at a specific time, where each engine implements multiple workflow instances. The host process interacts with runtime engine by using any of the following classes:

a) WorkflowInvoker - Requests a workflow as its method.

b) WorkflowApplication - Controls the implementation of a single workflow instance explicitly.

c) WorkflowServiceHost - Hosts the workflows and permits sending and receiving messages among various instances of workflows.