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join_node

join_node#

[flow_graph.join_node]

A node that creates a tuple from a set of messages received at its input ports and broadcasts the tuple to all of its successors.

// Defined in header <oneapi/tbb/flow_graph.h>

namespace oneapi {
namespace tbb {
namespace flow {
    using tag_value = /*implementation-specific*/;

    template<typename OutputTuple, class JoinPolicy = /*implementation-defined*/>
    class join_node : public graph_node, public sender< OutputTuple > {
    public:
        using input_ports_type = /*implementation-defined*/;

        explicit join_node( graph &g );
        join_node( const join_node &src );

        input_ports_type &input_ports( );

        bool try_get( OutputTuple &v );
    };

    template<typename OutputTuple, typename K, class KHash=tbb_hash_compare<K> >
    class join_node< OutputTuple, key_matching<K,KHash> > : public graph_node, public sender< OutputTuple > {
    public:
        using input_ports_type = /*implementation-defined*/;

        explicit join_node( graph &g );
        join_node( const join_node &src );

        template <typename B0, typename... BN>
        join_node( graph &g, B0 b0, BN... bn );

        input_ports_type &input_ports( );

        bool try_get( OutputTuple &v );
    };

} // namespace flow
} // namespace tbb
} // namespace oneapi

Requirements:

  • The type OutputTuple must be an instantiation of std::tuple. Each type that the tuple stores must meet the DefaultConstructible requirements from [defaultconstructible], CopyConstructible requirements from [copyconstructible] and CopyAssignable requirements from [copyassignable] ISO C++ Standard sections.

  • The JoinPolicy type must be specified as one of buffering policies for join_node.

  • The KHash type must meet the HashCompare requirements.

  • The Bi types must meet the JoinNodeFunctionObject requirements. Since C++17, each of Bi types may also be a pointer to a const member function in Input that returns Key or a pointer to a data member of type Key in Input.

A join_node is a graph_node and a sender<OutputTuple>. It contains a tuple of input ports, each of which is a receiver<Type> for each Type in OutputTuple. It supports multiple input receivers with distinct types and broadcasts a tuple of received messages to all of its successors. All input ports of a join_node must use the same buffering policy.

The behavior of a join_node is based on its buffering policy.

The function template input_port simplifies the syntax for getting a reference to a specific input port.

join_node has a buffering and broadcast-push properties.

Member types#

input_ports_type is an alias to a tuple of input ports.

Member functions#

explicit join_node( graph &g );

Constructs an empty join_node that belongs to the graph g.

template <typename B0, typename... BN>
join_node( graph &g, B0 b0, BN... bn );

A constructor only available in the key_matching specialization of join_node.

Creates a join_node that uses the function objects b0, … , bN to determine the tags for the input ports 0 through N.

Constraints:: only participates in overload resolution if std::tuple_size<OutputTuple>::value is 1 + sizeof...(BN).

Caution

Function objects passed to the join_node constructor must not throw. They are called in parallel, and should be pure, take minimal time, and be non-blocking.

join_node( const join_node &src )

Creates a join_node that has the same initial state that src had at its construction. The list of predecessors, messages in the input ports, and successors are not copied.

input_ports_type &input_ports( )

Returns: a std::tuple of receivers. Each element inherits values from receiver<T>, where T is the type of message expected at that input. Each tuple element can be used like any other receiver<T>. The behavior of the ports is based on the selected join_node policy.

bool try_get( output_type &v )

Attempts to generate a tuple based on the buffering policy of the join_node.

If it can successfully generate a tuple, it copies it to v and returns true. Otherwise, it returns false.

Non-Member Types#

using tag_value = /*implementation-specific*/;

tag_value is an unsigned integral type for defining the tag_matching policy.

Deduction Guides#

template <typename Body, typename... Bodies>
join_node(graph&, Body, Bodies...)
    ->join_node<std::tuple<std::decay_t<input_t<Body>>, std::decay_t<input_t<Bodies>>...>, key_matching<output_t<Body>>>;

Where:

  • input_t is an alias to the input argument type of the passed function object.

  • output_t is an alias to the return type of the passed function object.

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