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<h1 class="topictitle1">write_once_node Template Class</h1>
<div>
<div class="section"><h2 class="sectiontitle">Summary</h2>
<p>A template class that is a
<span class="keyword">graph_node</span>,
<span class="keyword">receiver<Input></span> and
<span class="keyword">sender<Output></span>. A
<span class="keyword">write_once_node</span> 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.
</p>
<p>Rejection of messages by successors is handled using the protocol in
the Message Passing Protocol, see link below.
</p>
<p><span class="keyword">T</span> must be copy-constructible and assignable
</p>
</div>
<div class="section"><h2 class="sectiontitle">Syntax</h2>
<pre>template < typename T > class write_once_node;</pre>
</div>
<div class="section"><h2 class="sectiontitle">Header</h2>
<pre>#include "tbb/flow_graph.h"</pre>
</div>
<div class="section"><h2 class="sectiontitle">Members</h2>
<pre>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( );
};
}
}</pre>
<div class="tablenoborder"><table cellpadding="4" summary="" frame="border" border="1" cellspacing="0" rules="all"><span class="tabledesc">The following table provides additional information on the
members of this template class.
</span><thead align="left">
<tr>
<th class="cellrowborder" valign="top" width="33.89830508474576%" id="d87805e152">Member
</th>
<th class="cellrowborder" valign="top" width="66.10169491525423%" id="d87805e155">Description
</th>
</tr>
</thead>
<tbody>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d87805e152 "><span class="keyword">write_once_node( graph &g
)</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d87805e155 ">
<p>Constructs an object of type
<span class="keyword">write_once_node</span> that belongs to the
<span class="keyword">graph g</span>, with an invalid internal buffer
item.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d87805e152 "><span class="keyword">write_once_node( const
write_once_node &src )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d87805e155 ">
<p>Constructs an object of type
<span class="keyword">write_once_node</span> with an invalid internal
buffer item. The buffered value and list of successors is NOT copied from
<span class="keyword">src</span>.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d87805e152 "><span class="keyword">bool try_put( const input_type
&v )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d87805e155 ">
<p>Stores<span class="keyword"> v</span> in the internal single item
buffer if it does not already contain a valid value. If a new value is set, it
calls
<span class="keyword">try_put(v)</span> on all successors.
</p>
<p><strong>Returns</strong>:
<span class="keyword">true</span>
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d87805e152 "><span class="keyword">bool register_predecessor(
predecessor_type &p )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d87805e155 ">
<p>Never rejects puts and therefore does not need to maintain a
list of predecessors.
</p>
<p><strong>Returns</strong>:
<span class="keyword">false</span>
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d87805e152 "><span class="keyword">bool remove_predecessor(
predecessor_type &p )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d87805e155 ">
<p>Never rejects puts and therefore does not need to maintain a
list of predecessors.
</p>
<p><strong>Returns</strong>:
<span class="keyword">false</span>
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d87805e152 "><span class="keyword">bool register_successor(
successor_type &r )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d87805e155 ">
<p>Adds
<span class="keyword">r</span> to the set of successors. If a valid
item
<span class="keyword">v</span> is held in the buffer, a task is
spawned to call
<span class="keyword">r.try_put(v)</span>.
</p>
<p><strong>Returns</strong>:
<span class="keyword">true</span>
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d87805e152 "><span class="keyword">bool remove_successor(
successor_type &r )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d87805e155 ">
<p>Removes
<span class="keyword">r</span> from the set of successors.
</p>
<p><strong>Returns</strong>:
<span class="keyword">true</span>
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d87805e152 "><span class="keyword">bool try_get( output_type &v
)</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d87805e155 ">
<p>If the internal buffer is valid, assigns the value to
<span class="keyword">v</span>.
</p>
<p><strong>Returns</strong>:
<span class="keyword">true</span> if
<span class="keyword">v</span> is assigned to.
<span class="keyword">false</span> if
<span class="keyword">v</span> is not assigned to.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d87805e152 "><span class="keyword">bool try_reserve( output_type
&v )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d87805e155 ">
<p>Does not support reservations.
</p>
<p><strong>Returns</strong>:
<span class="keyword">false</span>
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d87805e152 "><span class="keyword">bool try_release( )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d87805e155 ">
<p>Does not support reservations.
</p>
<p><strong>Returns</strong>:
<span class="keyword">false</span>
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d87805e152 "><span class="keyword">bool try_consume( )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d87805e155 ">
<p>Does not support reservations.
</p>
<p><strong>Returns</strong>:
<span class="keyword">false</span>
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d87805e152 "><span class="keyword">bool is_valid( )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d87805e155 ">
<p><strong>Returns</strong>:
<span class="keyword">true</span> if the buffer holds a valid value,
otherwise returns
<span class="keyword">false</span>.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d87805e152 "><span class="keyword">void clear( )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d87805e155 ">
<p>Invalidates the value held in the buffer.
</p>
</td>
</tr>
</tbody>
</table>
</div>
</div>
</div>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="../../reference/flow_graph.htm">Flow Graph</a></div>
</div>
<div class="See Also">
<h2>See Also</h2>
<div class="linklist">
<div><a href="message_passing_protocol.htm">Message Passing Protocol
</a></div></div>
</div>
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