Flow Graph


In addition to loop parallelism, the oneAPI Threading Building Blocks library also supports graph parallelism. It’s possible to create graphs that are highly scalable, but it is also possible to create graphs that are completely sequential.

There are 3 types of components used to implement a graph:

  • A graph class instance

  • Nodes

  • Ports and edges

Graph Class

The graph class instance is the owner of the tasks created on behalf of the flow graph. Users can wait on the graph if they need to wait for the completion of all of the tasks related to the flow graph execution. One can also register external interactions with the graph and run tasks under the ownership of the flow graph.


Abstract Interfaces

In order to be used as a graph node type, a class needs to inherit certain abstract types and implement the corresponding interfaces. graph_node is the base class for any other node type; its interfaces always have to be implemented. If a node sends messages to other nodes, it has to implement the sender interface, while with receiver interface the node may accept messages. For nodes that have multiple inputs and/or outputs, each input port is a receiver and each output port is a sender.


Every node in flow graph has its own properties.

Functional Nodes

Functional nodes do computations in response to input messages (if any), and send the result or a signal to their successors.


Buffering Nodes

Buffering nodes are designed to accumulate input messages and pass them to successors in a predefined order, depending on the node type.

Service Nodes

These nodes are designed for advanced control of the message flow, such as combining messages from different paths in a graph or limiting the number of simultaneously processed messages, as well as for creating reusable custom nodes.

Ports and Edges

Flow Graph provides an API to manage connections between the nodes. For nodes that have more than one input or output port (ex. join_node), making a connection requires to specify a certain port by using special helper functions.

Special Messages Types

Flow Graph supports a set of specific message types.