Flow Graph Basics: Graph Object

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();

The graph object does not own the nodes associated with it. You need to make sure that the graph object’s lifetime is longer than the lifetimes of all nodes added to the graph and any activity associated with the graph.

Tip

Call wait_for_all on a graph object before destroying it to make sure all activities are complete.

Even when using smart pointers, be aware of the order of destruction for nodes and the graph to make sure that nodes are not deleted before the graph.