Conceptually a flow graph is a collection of nodes and edges. Each node belongs to exactly one graph and edges are made only between nodes in the same graph. In the flow graph interface, a graph object represents this collection of nodes and edges, and is used for invoking whole graph operations such as waiting for all tasks related to the graph to complete, resetting the state of all nodes in the graph, and canceling the execution of all nodes in the graph.
The code below creates a graph object and then waits for all tasks spawned by the graph to complete. The call to wait_for_all in this example returns immediately since this is a trivial graph with no nodes or edges, and therefore no tasks are spawned.
graph g; g.wait_for_all();