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<h1 class="topictitle1">limiter_node Template Class</h1>
<div>
<div class="section"><h2 class="sectiontitle">Summary</h2>
<p>An node that counts and limits the number of messages that pass
through it.
</p>
</div>
<div class="section"><h2 class="sectiontitle">Syntax</h2>
<pre>template < typename T > class limiter_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">Description</h2>
<p>A
<span class="keyword">limiter_node</span> is a
<span class="keyword">graph_node</span>,
<span class="keyword">receiver<T></span> and
<span class="keyword">sender<T></span> that broadcasts messages to all of
its successors. It keeps a counter C of the number of broadcasts it makes and
does not accept new messages once its user-specified
<span class="keyword">threshold</span> is reached. The internal count of
broadcasts C can be decremented through use of its embedded
<span class="keyword">continue_receiver decrement</span>.
</p>
<p>The behavior of a call to a
<span class="keyword">limiter_node</span>'s
<span class="keyword">try_put</span> is shown below.
</p>
<div class="tablenoborder"><a name="tbl27"><!-- --></a><table cellpadding="4" summary="" id="tbl27" frame="border" border="1" cellspacing="0" rules="all"><caption><span class="tablecap">Behavior of a call to a limiter_node's try_put</span></caption>
<thead align="left">
<tr>
<th class="cellrowborder" align="center" valign="top" width="30%" id="d75154e95">
<p>Value of counter C
</p>
</th>
<th class="cellrowborder" align="center" valign="top" width="70%" id="d75154e101">
<p>bool try_put( const input_type &v )
</p>
</th>
</tr>
</thead>
<tbody>
<tr>
<td class="cellrowborder" valign="top" width="30%" headers="d75154e95 ">
<p>C < threshold
</p>
</td>
<td class="cellrowborder" valign="top" width="70%" headers="d75154e101 ">
<p>C is incremented and
<span class="keyword">v</span> is broadcast to all successors. If no
successor accepts the message, C is decremented. Returns
<span class="keyword">true</span> if the message was successfully
broadcast to at least one successor and
<span class="keyword">false</span> otherwise.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="30%" headers="d75154e95 ">
<p>C == threshold
</p>
</td>
<td class="cellrowborder" valign="top" width="70%" headers="d75154e101 ">
<p>Returns
<span class="keyword">false</span>.
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>When
<span class="keyword">try_put</span> is called on the member object
<span class="keyword">decrement</span>, the
<span class="keyword">limiter_node</span> will try to get a message from one of
its known predecessors and forward that message to all of its successors. If it
cannot obtain a message from a predecessor, it will decrement C. Rejection of
messages by successors and failed gets from predecessors are 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">Members</h2>
<pre>namespace tbb {
namespace flow {
template< typename T >
class limiter_node : public graph_node, public receiver<T>,
public sender<T> {
public:
limiter_node( graph &g, size_t threshold,
int number_of_decrement_predecessors = 0 );
limiter_node( const limiter_node &src );
// a continue_receiver
implementation-dependent-type decrement;
// 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( );
};
}
}</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="d75154e260">Member
</th>
<th class="cellrowborder" valign="top" width="66.10169491525423%" id="d75154e263">Description
</th>
</tr>
</thead>
<tbody>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d75154e260 "><span class="keyword">limiter_node( graph &g, size_t
threshold, int number_of_decrement_predecessors = 0 )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d75154e263 ">
<p>Constructs a
<span class="keyword">limiter_node</span> that allows up to
<span class="keyword">threshold</span> items to pass through before
rejecting
<span class="keyword">try_put</span>'s. Optionally a
<span class="keyword">number_of_decrement_predecessors</span> value can
be supplied. This value is passed on to the
<span class="keyword">continue_receiver decrement</span>'s constructor.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d75154e260 "><span class="keyword">limiter_node( const limiter_node
&src )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d75154e263 ">
<p>Constructs a
<span class="keyword">limiter_node</span> that has the same initial
state that
<span class="keyword">src</span> had at its construction. The new
<span class="keyword">limiter_node</span> will belong to the same
<span class="keyword">graph g</span> as
<span class="keyword">src</span>, have the same
<span class="keyword">threshold</span>, and have the same initial
<span class="keyword">number_of_decrement_predecessors</span>. The list
of predecessors, the list of successors, and the current count of broadcasts,
C, are NOT copied from
<span class="keyword">src</span>.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d75154e260 "><span class="keyword">bool try_put( const input_type
&v )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d75154e263 ">
<p>If the broadcast count is below the threshold,
<span class="keyword">v</span> is broadcast to all successors. For each
successor
<span class="keyword">s</span>, if
<span class="keyword">s.try_put( v ) == false &&
s.register_predecessor( *this ) == true</span>, then
<span class="keyword">s</span> is removed from the set of succesors.
Otherwise,
<span class="keyword">s</span> will remain in the set of successors.
</p>
<p><strong>Returns</strong>:
<span class="keyword">true</span> if
<span class="keyword">v</span> is broadcast.
<span class="keyword">false</span> if
<span class="keyword">v</span> is not broadcast because the threshold
has been reached.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d75154e260 "><span class="keyword">bool register_predecessor(
predecessor_type &p )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d75154e263 ">
<p>Adds a predecessor that can be pulled from once the
broadcast count falls below the threshold.
</p>
<p>Adds
<span class="keyword">p</span> to the set of predecessors.
</p>
<p><strong>Returns</strong>:<span class="keyword">true</span>.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d75154e260 "><span class="keyword">bool remove_predecessor(
predecessor_type &p )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d75154e263 ">
<p>Removes
<span class="keyword">p</span> from the set of predecessors.
</p>
<p><strong>Returns</strong>:
<span class="keyword">true</span>
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d75154e260 "><span class="keyword">bool register_successor(
successor_type &r )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d75154e263 ">
<p>Adds
<span class="keyword">r</span> to 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="d75154e260 "><span class="keyword">bool remove_successor(
successor_type &r )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d75154e263 ">
<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="d75154e260 "><span class="keyword">bool try_get( output_type &v
)</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d75154e263 ">
<p>Does not contain buffering and therefore cannot be pulled
from.
</p>
<p><strong>Returns</strong>:
<span class="keyword">false</span>.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d75154e260 "><span class="keyword">bool try_reserve( output_type
&v )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d75154e263 ">
<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="d75154e260 "><span class="keyword">bool try_release( )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d75154e263 ">
<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="d75154e260 "><span class="keyword">bool try_consume( )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d75154e263 ">
<p>Does not support reservations.
</p>
<p><strong>Returns</strong>:
<span class="keyword">false</span>.
</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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