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async_node

async_node#

[flow_graph.async_node]

A node that enables communication between a flow graph and an external activity managed by the user or another runtime.

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

namespace oneapi {
namespace tbb {
namespace flow {

    template < typename Input, typename Output, typename Policy = /*implemetation-defined*/ >
    class async_node : public graph_node, public receiver<Input>, public sender<Output> {
    public:
        template<typename Body>
        async_node( graph &g, size_t concurrency, Body body, Policy /*unspecified*/ = Policy(),
                    node_priority_t priority = no_priority );
        template<typename Body>
        async_node( graph &g, size_t concurrency, Body body, node_priority_t priority = no_priority );

        async_node( const async_node& src );
        ~async_node();

        using gateway_type = /*implementation-defined*/;
        gateway_type& gateway();

        bool try_put( const input_type& v );
        bool try_get( output_type& v );
    };

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

Requirements:

  • The Input type must meet the DefaultConstructible requirements from [defaultconstructible] and the CopyConstructible requirements from [copyconstructible] ISO C++ Standard sections.

  • The type Policy can be specified as lightweight, queueing and rejecting policies or defaulted.

  • The type Body must meet the AsyncNodeBody requirements. Since C++17, Body may also be a pointer to a const member function in Input that takes gateway_type& argument.

async_node executes a user-provided body on incoming messages. The body typically submits the messages to an external activity for processing outside of the graph. It is responsibility of body to be able to pass the message to an external activity. This node also provides the gateway_type interface that allows an external activity to communicate with the flow graph.

async_node is a graph_node, receiver<Input>, and a sender<Output>.

async_node has a discarding and broadcast-push properties.

async_node has a user-settable concurrency limit, which can be set to one of predefined values. The user can also provide a value of type std::size_t to limit concurrency to a value between 1 and tbb::flow::unlimited.

The body object passed to a async_node is copied. Updates to member variables do not affect the original object used to construct the node. If the state held within a body object must be inspected from outside of the node, the copy_body function can be used to obtain an updated copy.

Member types#

gateway_type meets the GatewayType requirements.

Member functions#

template<typename Body>
async_node( graph &g, size_t concurrency, Body body,
               node_priority_t priority = no_priority );

Constructs an async_node that invokes a copy of body. The concurrency value limits the number of simultaneous body invocations for the node.

This function specifies node priority.

template<typename Body>
async_node( graph &g, size_t concurrency, Body body, Policy /*unspecified*/ = Policy(),
               node_priority_t priority = no_priority );

Constructs a async_node that invokes a copy of body. Most concurrency calls to body can be made concurrently.

This function specifies a policy and node priority.

async_node( const async_node &src )

Constructs an async_node that has the same initial state that src had when it was constructed. The async_node that is constructed has a reference to the same graph object as src, has a copy of the initial body used by src, and has the same concurrency threshold as src. The predecessors and successors of src are not copied.

The new body object is copy-constructed from a copy of the original body provided to src at its construction. Changes made to member variables in src’s body after the construction of src do not affect the body of the new async_node.

gateway_type& gateway()

Returns reference to the gateway_type interface.

bool try_put( const input_type& v )

If the concurrency limit allows, executes the user-provided body on the incoming message v. Otherwise, depending on the policy of the node, either queues the incoming message v or rejects it.

Returns: true if the input was accepted; and false, otherwise.

bool try_get( output_type& v )

Returns: false

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