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<h1 class="topictitle1">concurrent_priority_queue Template
Class</h1>
<div>
<div class="section"><h2 class="sectiontitle">Summary</h2>
<p>Template class for priority queue with concurrent
operations.
</p>
</div>
<div class="section"><h2 class="sectiontitle">Syntax</h2>
<p>
<pre>template<typename T, typename Alloc=cache_aligned_allocator<T> > class concurrent_priority_queue;</pre>
</p>
</div>
<div class="section"><h2 class="sectiontitle">Header</h2>
<p>
<pre>#include "tbb/concurrent_priority_queue.h"</pre>
</p>
</div>
<div class="section"><h2 class="sectiontitle">Description</h2>
<p>A
<samp class="codeph">concurrent_priority_queue</samp> is a container that permits
multiple threads to concurrently push and pop items. Items are popped in
priority order as determined by a template parameter. The capacity of the queue
is unbounded, subject to memory limitations on the target machine.
</p>
<p>The interface is similar to STL
<samp class="codeph">std::priority_queue</samp> except where it must differ to
make concurrent modification safe.
</p>
<div class="tablenoborder"><table cellpadding="4" summary="" width="100%" frame="hsides" border="1" rules="all"><caption><span class="tablecap">Differences Between STL queue and Intel®
Threading Building Blocks concurrent_priority_queue</span></caption>
<thead align="left">
<tr>
<th class="cellrowborder" valign="top" width="NaN%" id="d37381e84">
<p>Feature
</p>
</th>
<th class="cellrowborder" valign="top" width="NaN%" id="d37381e90">
<p>STL std::priority_queue
</p>
</th>
<th class="row-nocellborder" valign="top" width="NaN%" id="d37381e96">
<p>concurrent_priority_queue
</p>
</th>
</tr>
</thead>
<tbody>
<tr>
<td class="cellrowborder" valign="top" width="NaN%" headers="d37381e84 ">
<p>Choice of underlying container
</p>
</td>
<td class="cellrowborder" valign="top" width="NaN%" headers="d37381e90 ">
<p>Sequence template parameter
</p>
</td>
<td class="row-nocellborder" valign="top" width="NaN%" headers="d37381e96 ">
<p>No choice of underlying container;
allocator choice is provided instead
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="NaN%" headers="d37381e84 ">
<p>Access to highest priority item
</p>
</td>
<td class="cellrowborder" valign="top" width="NaN%" headers="d37381e90 ">
<p><samp class="codeph">const value_type& top()
const</samp>
</p>
</td>
<td class="row-nocellborder" valign="top" width="NaN%" headers="d37381e96 ">
<p>Not available. Unsafe for concurrent
container
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="NaN%" headers="d37381e84 ">
<p>Copy and pop item if present
</p>
</td>
<td class="cellrowborder" valign="top" width="NaN%" headers="d37381e90 ">
<p><samp class="codeph">bool b=!q.empty(); if(b) {
x=q.top(); q.pop(); }</samp>
</p>
</td>
<td class="row-nocellborder" valign="top" width="NaN%" headers="d37381e96 ">
<p><samp class="codeph">bool b = q.try_pop(x);</samp>
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="NaN%" headers="d37381e84 ">
<p>Get number of items in queue
</p>
</td>
<td class="cellrowborder" valign="top" width="NaN%" headers="d37381e90 ">
<p><samp class="codeph">size_type size() const</samp>
</p>
</td>
<td class="row-nocellborder" valign="top" width="NaN%" headers="d37381e96 ">
<p>Same, but may be inaccurate due to pending
concurrent push or pop operations
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="NaN%" headers="d37381e84 ">
<p>Check if there are items in queue
</p>
</td>
<td class="cellrowborder" valign="top" width="NaN%" headers="d37381e90 ">
<p><samp class="codeph">bool empty() const</samp>
</p>
</td>
<td class="row-nocellborder" valign="top" width="NaN%" headers="d37381e96 ">
<p>Same, but may be inaccurate due to pending concurrent push or
pop operations
</p>
</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section"><h2 class="sectiontitle">Members</h2>
<pre>namespace tbb {
template <typename T, typename Compare=std::less<T>,
typename A=cache_aligned_allocator<T> >
class concurrent_priority_queue {
typedef T value_type;
typedef T& reference;
typedef const T& const_reference;
typedef size_t size_type;
typedef ptrdiff_t difference_type;
typedef A allocator_type;
//Constructors
concurrent_priority_queue(const allocator_type& a = allocator_type());
concurrent_priority_queue(size_type init_capacity, const allocator_type& a = allocator_type());
template<typename InputIterator>
concurrent_priority_queue(InputIterator begin, InputIterator end, const allocator_type& a = allocator_type());
concurrent_priority_queue(const concurrent_priority_queue& src, const allocator_type& a = allocator_type());
//C++11 specific
concurrent_priority_queue(const std::initializer_list<T> & il, const allocator_type &a = allocator_type());
//Assignment
concurrent_priority_queue& operator=(const concurrent_priority_queue& src);
template<typename InputIterator>
void assign(InputIterator begin, InputIterator end);
//C++11 specific
concurrent_priority_queue& operator=(const std::initializer_list<T> & il);
void assign(const std::initializer_list<T> & il);
void swap(concurrent_priority_queue& other);
~concurrent_priority_queue();
allocator_type get_allocator() const;
bool empty() const;
size_type size() const;
void push(const_reference elem);
bool try_pop(reference elem);
void clear();
};
}
</pre>
<div class="Note"><h3 class="NoteTipHead">
Note</h3>
<p>In Intel® Threading Building Blocks (Intel® TBB) 2.1, a
<samp class="codeph">concurrent_queue</samp> could be bounded. Intel® TBB 2.2
moves this functionality to
<samp class="codeph">concurrent_bounded_queue</samp>. Compile with
<samp class="codeph">TBB_DEPRECATED=1</samp> to restore the old functionality,
or (recommended) use
<samp class="codeph">concurrent_bounded_queue</samp> instead.
</p>
</div>
<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="d37381e263">Member
</th>
<th class="cellrowborder" valign="top" width="66.10169491525423%" id="d37381e266">Description
</th>
</tr>
</thead>
<tbody>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d37381e263 "><span class="keyword">concurrent_priority_queue(const
allocator_type& a = allocator_type())</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d37381e266 ">
<p>Constructs empty queue.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d37381e263 "><span class="keyword">concurrent_priority_queue(size_type init_capacity,
const allocator_type& a = allocator_type())</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d37381e266 ">
<p>Constructs an empty queue with an initial capacity.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d37381e263 "><span class="keyword">template <typename InputIterator> concurrent_priority_queue(InputIterator begin,
InputIterator end, const allocator_type& a = allocator_type())</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d37381e266 ">
<p>Constructs a queue containing copies of elements in the
iterator half-open interval
<samp class="codeph">[begin, end)</samp>.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d37381e263 "><span class="keyword">concurrent_priority_queue(const std::initializer_list<T> & il,
const allocator_type &a = allocator_type())</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d37381e266 ">
<p>C++11 specific; Equivalent to <samp class="codeph">concurrent_priority_queue(<em>il</em>.begin(), <em>il</em>.end(), <em>a</em>)</samp>.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d37381e263 "><span class="keyword">concurrent_priority_queue (const
concurrent_priority_queue& src, const allocator_type& a =
allocator_type())</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d37381e266 ">
<p>Constructs a copy of
<samp class="codeph">src</samp>. This operation is not thread-safe and
may result in an error or an invalid copy of
<samp class="codeph">src</samp> if another thread is concurrently
modifying
<samp class="codeph">src.</samp>
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d37381e263 "><span class="keyword">concurrent_priority_queue&
operator=(const concurrent_priority_queue& src)</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d37381e266 ">
<p>Assign contents of
<samp class="codeph">src</samp> to
<samp class="codeph">*this</samp>. This operation is not thread-safe and
may result in an error or an invalid copy of
<samp class="codeph">src</samp> if another thread is concurrently
modifying
<samp class="codeph">src</samp>.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d37381e263 "><span class="keyword">concurrent_priority_queue&
operator=(const std::initializer_list<T> & il)</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d37381e266 ">
<p>C++11 specific; Sets
<samp class="codeph">*<em>this</em></samp>
to contain data from
<samp class="codeph">il</samp>.
<strong>Returns</strong>: reference to <samp class="codeph">*this</samp>.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d37381e263 "><span class="keyword">template <typename InputIterator> void assign(InputIterator begin,
InputIterator end, const allocator_type&)</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d37381e266 ">
<p>Assign contents of the
iterator half-open interval
<samp class="codeph">[begin, end)</samp> to <samp class="codeph">*this</samp>.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d37381e263 "><span class="keyword">void assign(const std::initializer_list<T> & il)</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d37381e266 ">
<p>C++11 specific; Equivalent to <samp class="codeph">assign(<em>il</em>.begin(), <em>il</em>.end())</samp>.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d37381e263 "><span class="keyword">~concurrent_priority_queue()</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d37381e266 ">
<p>Destroys all items in the queue, and the container itself,
so that it can no longer be used.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d37381e263 "><span class="keyword">bool empty() const</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d37381e266 ">
<p><strong>Returns</strong>:
<samp class="codeph">true</samp> if queue has no items;
<samp class="codeph">false</samp> otherwise. May be inaccurate when
concurrent
<samp class="codeph">push</samp> or
<samp class="codeph">try_pop</samp> operations are pending. This
operation reads shared data and may trigger a race condition in race detection
tools when used concurrently.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d37381e263 "><span class="keyword">size_type size() const</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d37381e266 ">
<p><strong>Returns</strong>: Number of items in the queue. May be
inaccurate when concurrent
<samp class="codeph">push</samp> or
<samp class="codeph">try_pop</samp> operations are pending. This
operation reads shared data and may trigger a race condition in race detection
tools when used concurrently.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d37381e263 "><span class="keyword">void push(const_reference
elem)</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d37381e266 ">
<p>Pushes a copy of
<samp class="codeph">elem</samp> into the queue. This operation is
thread-safe with other
<samp class="codeph">push</samp> and
<samp class="codeph">try_pop</samp> operations.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d37381e263 "><span class="keyword"> bool try_pop(reference
elem)</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d37381e266 ">
<p>If the queue is not empty, copies the highest priority item
from the queue and assigns it to
<samp class="codeph">elem</samp>, and destroys the popped item in the
queue; otherwise, does nothing. This operation is thread-safe with other
<samp class="codeph">push</samp> and
<samp class="codeph">try_pop</samp> operations.
</p>
<p><strong>Returns</strong>:
<samp class="codeph">true</samp> if an item was popped;
<samp class="codeph">false</samp> otherwise.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d37381e263 "><span class="keyword"> void clear()</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d37381e266 ">
<p>Clears the queue; results in
<samp class="codeph">size()==0</samp>. This operation is not
thread-safe.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d37381e263 "><span class="keyword"> void
swap(concurrent_priority_queue& other)</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d37381e266 ">
<p>Swaps the queue contents with those of other. This operation
is not thread-safe.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d37381e263 "><span class="keyword"> allocator_type get_allocator()
const</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d37381e266 ">
<p><strong>Returns</strong>: Copy of allocator used to construct the
queue.
</p>
</td>
</tr>
</tbody>
</table>
</div>
</div>
</div>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="../../reference/containers_overview.htm">Containers Overview</a></div>
</div>
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