write_once_node Template Class

Summary

A template class that is a graph_node, receiver<Input> and sender<Output>. A write_once_node represents a buffer of a single item that cannot be over-written. The first put to the node sets the value. The value may be cleared explicitly, after which a new value may be set. Gets from the node are non-destructive.

Rejection of messages by successors is handled using the protocol in the Message Passing Protocol, see link below.

T must be copy-constructible and assignable

Syntax

template < typename T > class write_once_node;

Header

#include "tbb/flow_graph.h"

Members

namespace tbb {
namespace flow {
 
template< typename T >
class write_once_node :
  public graph_node, public receiver<T>,
  public sender<T> {
public:
    write_once_node( graph &g );
    write_once_node( const write_once_node &src );
 
    // receiver<T>
    typedef T input_type;
    typedef sender<input_type> predecessor_type;
    bool try_put( const input_type &v );
    bool register_predecessor( predecessor_type &p );
    bool remove_predecessor( predecessor_type &p );
 
    // sender<T>
    typedef T output_type;
    typedef receiver<output_type> successor_type;
    bool register_successor( successor_type &r );
    bool remove_successor( successor_type &r );
    bool try_get( output_type &v );
    bool try_reserve( output_type &v );
    bool try_release( );
    bool try_consume( );
 
    bool is_valid( );
    void clear( );
};
 
}
}
The following table provides additional information on the members of this template class.
Member Description
write_once_node( graph &g )

Constructs an object of type write_once_node that belongs to the graph g, with an invalid internal buffer item.

write_once_node( const write_once_node &src )

Constructs an object of type write_once_node with an invalid internal buffer item. The buffered value and list of successors is NOT copied from src.

bool try_put( const input_type &v )

Stores v in the internal single item buffer if it does not already contain a valid value. If a new value is set, it calls try_put(v) on all successors.

Returns: true

bool register_predecessor( predecessor_type &p )

Never rejects puts and therefore does not need to maintain a list of predecessors.

Returns: false

bool remove_predecessor( predecessor_type &p )

Never rejects puts and therefore does not need to maintain a list of predecessors.

Returns: false

bool register_successor( successor_type &r )

Adds r to the set of successors. If a valid item v is held in the buffer, a task is enqueued to call r.try_put(v).

Returns: true

bool remove_successor( successor_type &r )

Removes r from the set of successors.

Returns: true

bool try_get( output_type &v )

If the internal buffer is valid, assigns the value to v.

Returns: true if v is assigned to. false if v is not assigned to.

bool try_reserve( output_type &v )

Does not support reservations.

Returns: false

bool try_release( )

Does not support reservations.

Returns: false

bool try_consume( )

Does not support reservations.

Returns: false

bool is_valid( )

Returns: true if the buffer holds a valid value, otherwise returns false.

void clear( )

Invalidates the value held in the buffer.

See Also