# composite_node Template Class¶

## Summary¶

A node that encapsulates a collection of other nodes as a first class graph node. The use of composite_node requires C++11 support. On Microsoft Windows*, at least Visual Studio 2013 is required.

## Syntax¶

template<typename InputTuple, typename OutputTuple>
class composite_node;


## Description¶

The composite_node can package any number of other nodes. It maintains input and output port references to nodes in the package that border the composite_node. This allows for the references to be used to make edges to other nodes outside of the composite_node. The InputTuple is a tuple of input types. The composite_node has an input port for each type in InputTuple. Likewise, the OutputTuple is a tuple of output types. The composite_node has an output port for each type in OutputTuple.

The composite_node is a multi-port node with three specializations.

• A multi-port node with multi-input ports and multi-output ports: This specialization has a tuple of input ports, each of which is a receiver of a type in InputTuple. Each input port is a reference to a port of a node that the composite_node encapsulates. Similarly, this specialization also has a tuple of output ports, each of which is a sender of a type in OutputTuple. Each output port is a reference to a port of a node that the composite_node encapsulates.

• A multi-port node with only input ports and no output ports: This specialization only has a tuple of input ports.

• A multi-port node with only output ports and no input_ports: This specialization only has a tuple of output ports.

The function template input_port can be used to get a reference to a specific input port and the function template output_port can be used to get a reference to a specific output port.

Construction of a composite_node is done in two stages:

• Defining the composite_node with specification of InputTuple and OutputTuple.

• Making aliases from the encapsulated nodes that border the composite_node to the input and output ports of the composite_node. This step is mandatory as without it the composite_node’s input and output ports would not have been bound to any actual nodes. Making the aliases is achieved by calling the method set_external_ports.

The composite_node is not copy-constructible.

## Example¶

#include "tbb/flow_graph.h"
#include <iostream>
#include <tuple>
using namespace tbb::flow;

class adder : public composite_node<  tuple<int, int>,  tuple<int> > {
join_node< tuple<int,int>, queueing > j;
function_node< tuple<int,int>, int > f;
typedef composite_node< tuple<int,int>, tuple<int> > base_type;

struct f_body {
int operator()(const tuple<int,int> &t) {
int n = (get<1>(t)+1)/2;
int sum = get<0>(t) + get<1>(t);
std::cout << "Sum of the first " << n <<" positive odd numbers is  " << n <<" squared: "  << sum << std::endl;
return  sum;
}
};

public:
adder(graph &g) : base_type(g), j(g), f(g, unlimited, f_body()) {
make_edge(j, f);
base_type::input_ports_type input_tuple(input_port<0>(j), input_port<1>(j));
base_type::output_ports_type output_tuple(f);
base_type::set_external_ports(input_tuple, output_tuple);
}
};

int main() {
graph g;
split_node< tuple<int, int, int, int> > s(g);

make_edge(output_port<0>(s), input_port<0>(a0));
make_edge(output_port<1>(s), input_port<1>(a0));

make_edge(output_port<0>(a0),input_port<0>(a1));
make_edge(output_port<2>(s), input_port<1>(a1));

make_edge(output_port<0>(a1), input_port<0>(a2));
make_edge(output_port<3>(s), input_port<1>(a2));

s.try_put(std::make_tuple(1,3,5,7));

g.wait_for_all();

return 0;
}


This example shows the use of composite_node to encapsulate two flow graph nodes (a join_node and a function_node). In the example the concept that the sum of the first n positive odd numbers is the same as n squared is demonstrated.

A class adder is defined. This class has a join_node j with two input ports and a function_node f. j receives a number at each of its input ports and sends a tuple of these numbers to f which adds the numbers. To encapsulate these two nodes, the adder inherits from a composite_node type with two input ports and one output port to match the two input ports of j and the one output port of f.

A split_node s is created to serve as the source of the positive odd numbers. The first four positive odd numbers 1, 3, 5 and 7 are used. Three adders a0, a1 and a2 are created. The first adder a0 receives 1 and 3 from the split_node. These are added and the sum forwarded to a1. The second adder a1 receives the sum of 1 and 3 on one input port and receives 5 on the other input port from the split_node. These are also added and the sum forwarded to a2. Likewise, the third adder a2 receives the sum of 1, 3 and 5 on one input port and receives 7 on the other input port from the split_node. Each adder reports the sum it computes which is the square of the count of numbers accumulated when that adder is reached in the graph. The output of running the example is as follows:

Sum of the first 2 positive odd numbers is  2^2: 4
Sum of the first 3 positive odd numbers is  3^2: 9
Sum of the first 4 positive odd numbers is  4^2: 16


## Members¶

namespace tbb {
namespace flow {

template< typename InputTuple, typename OutputTuple > class composite_node;

//composite_node with both input ports and output ports
template< typename... InputTypes, typename... OutputTypes>
class composite_node <tbb::flow::tuple<InputTypes...>, tbb::flow::tuple<OutputTypes...> > : public graph_node {
public:
typedef tbb::flow::tuple< sender<OutputTypes>&... > output_ports_type;

composite_node( graph &g );
virtual ~composite_node();

void set_external_ports(input_ports_type&& input_ports_tuple, output_ports_type&& output_ports_tuple);
input_ports_type& input_ports();
output_ports_type& output_ports();
};

//composite_node with only input ports
template< typename... InputTypes>
class composite_node <tbb::flow::tuple<InputTypes...>, tbb::flow::tuple<> > : public graph_node{
public:

composite_node( graph &g );
virtual ~composite_node();

void set_external_ports(input_ports_type&& input_ports_tuple);
input_ports_type& input_ports();
};

//composite_nodes with only output_ports
template<typename... OutputTypes>
class composite_node <tbb::flow::tuple<>, tbb::flow::tuple<OutputTypes...> > : public graph_node{
public:
typedef tbb::flow::tuple< sender<OutputTypes>&... > output_ports_type;

composite_node( graph &g );
virtual ~composite_node();

void set_external_ports(output_ports_type&& output_ports_tuple);
output_ports_type& output_ports();
};
}
}


The following table provides additional information on the members of this template class.

Member, Description

composite_node( graph &g )

Constructs a composite_node that belongs to the graph g.

void set_external_ports(input_ports_type&& input_ports_tuple, output_ports_type&& output_ports_tuple);

Creates input and output ports of the composite_node as aliases to the ports referenced by input_ports_tuple and output_ports_tuple respectively. That is, a port referenced at position N in input_ports_tuple is mapped as the Nth input port of the composite_node, similarly for output ports.

input_ports_type& input_ports()

Returns: A flow::tuple of receivers. Each element is a reference to the actual node or input port that was aliased to that position in set_external_ports().

Caution

Calling input_ports() without a prior call to set_external_ports() results in undefined behavior.

output_ports_type& output_ports()

Returns: A flow::tuple of senders. Each element is a reference to the actual node or output port that was aliased to that position in set_external_ports().

Caution

Calling output_ports() without a prior call to set_external_ports() results in undefined behavior.