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<h1 class="topictitle1">concurrent_queue Template Class</h1>
<div>
<div class="section"><h2 class="sectiontitle">Summary</h2>
<p>Template class for 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_queue;</pre>
</p>
</div>
<div class="section"><h2 class="sectiontitle">Header</h2>
<p>
<pre>#include "tbb/concurrent_queue.h"</pre>
</p>
</div>
<div class="section"><h2 class="sectiontitle">Description</h2>
<p>A
<samp class="codeph">concurrent_queue</samp> is a first-in first-out data
structure that permits multiple threads to concurrently push and pop items. Its
capacity is unbounded, subject to memory limitations on the target machine.
</p>
<p>The interface is similar to STL
<samp class="codeph">std::queue</samp> except where it must differ to make
concurrent modification safe.
</p>
<p>
</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_queue</span></caption>
<thead align="left">
<tr>
<th class="cellrowborder" valign="top" width="NaN%" id="d39293e87">
<p><strong>Feature</strong>
</p>
</th>
<th class="cellrowborder" valign="top" width="NaN%" id="d39293e95">
<p><strong>STL std::queue</strong>
</p>
</th>
<th class="row-nocellborder" valign="top" width="NaN%" id="d39293e103">
<p><strong>concurrent_queue</strong>
</p>
</th>
</tr>
</thead>
<tbody>
<tr>
<td class="cellrowborder" valign="top" width="NaN%" headers="d39293e87 ">
<p>Access to front and back
</p>
</td>
<td class="cellrowborder" valign="top" width="NaN%" headers="d39293e95 ">
<p>Methods
<samp class="codeph">front</samp> and
<samp class="codeph">back</samp>
</p>
</td>
<td class="row-nocellborder" valign="top" width="NaN%" headers="d39293e103 ">
<p>Not present. They would be unsafe while
concurrent operations are in progress.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="NaN%" headers="d39293e87 ">
<p><samp class="codeph">size_type</samp>
</p>
</td>
<td class="cellrowborder" valign="top" width="NaN%" headers="d39293e95 ">
<p>unsigned integral type
</p>
</td>
<td class="row-nocellborder" valign="top" width="NaN%" headers="d39293e103 ">
<p><samp class="codeph"><em>signed</em></samp> integral
type
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="NaN%" headers="d39293e87 ">
<p><samp class="codeph">unsafe_size()</samp>
</p>
</td>
<td class="cellrowborder" valign="top" width="NaN%" headers="d39293e95 ">
<p>Returns number of items in queue
</p>
</td>
<td class="row-nocellborder" valign="top" width="NaN%" headers="d39293e103 ">
<p>Returns number of items in queue. May
return incorrect value if any
<samp class="codeph">push</samp> or
<samp class="codeph">try_pop</samp> operations are concurrently in flight.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="NaN%" headers="d39293e87 ">
<p>Copy and pop item unless queue q is empty.
</p>
</td>
<td class="cellrowborder" valign="top" width="NaN%" headers="d39293e95 ">
<p>bool b=!q.empty();
</p>
<p>if(b) {
</p>
<p> x=q.front();
</p>
<p> q.pop();
</p>
<p>}
</p>
</td>
<td class="row-nocellborder" valign="top" width="NaN%" headers="d39293e103 ">
<p>bool b =
<em>q</em>.try_pop (x)
</p>
</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section"><h2 class="sectiontitle">Members</h2>
<pre>namespace tbb {
template<typename T,
typename Alloc=cache_aligned_allocator<T> >
class concurrent_queue {
public:
<em>// types</em>
typedef T value_type;
typedef T& reference;
typedef const T& const_reference;
typedef std::ptrdiff_t size_type;
typedef std::ptrdiff_t difference_type;
typedef Alloc allocator_type;
explicit concurrent_queue(const Alloc& a = Alloc ());
concurrent_queue(const concurrent_queue& src,
const Alloc& a = Alloc());
template<typename InputIterator>
concurrent_queue(InputIterator first, InputIterator last,
const Alloc& a = Alloc());
~concurrent_queue();
void push( const T& source );
bool try_pop T& destination );
void clear() ;
size_type unsafe_size() const;
bool empty() const;
Alloc get_allocator() const;
typedef implementation-defined iterator;
typedef implementation-defined const_iterator;
// iterators (these are slow and intended only for debugging)
iterator unsafe_begin();
iterator unsafe_end();
const_iterator unsafe_begin() const;
const_iterator unsafe_end() const;
};
}</pre>
<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 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="d39293e275">Member
</th>
<th class="cellrowborder" valign="top" width="66.10169491525423%" id="d39293e278">Description
</th>
</tr>
</thead>
<tbody>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d39293e275 "><span class="keyword">concurrent_queue( const Alloc&
a = Alloc () )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d39293e278 ">
<p>Constructs empty queue.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d39293e275 "><span class="keyword">concurrent_queue( const
concurrent_queue& src, const Alloc& a = Alloc() )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d39293e278 ">
<p>Constructs a copy of
<em>src</em>.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d39293e275 "><span class="keyword">template<typename
InputIterator> concurrent_queue( InputIterator first, InputIterator last,
const Alloc& a = Alloc() )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d39293e278 ">
<p>Constructs a queue containing copies of elements in the
iterator half-open interval [<em>first,last</em>).
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d39293e275 "><span class="keyword">~concurrent_queue()</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d39293e278 ">
<p>Destroys all items in the queue.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d39293e275 "><span class="keyword">void push( const T& source
)</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d39293e278 ">
<p>Pushes a copy of
<samp class="codeph">source</samp> onto back of the queue.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d39293e275 "><span class="keyword">bool try_pop ( T& destination
)</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d39293e278 ">
<p>If value is available, pops it from the queue, assigns it to
destination, and destroys the original value. Otherwise does nothing.
</p>
<p><strong>Returns</strong>: True if value was popped; false otherwise.
</p>
<div class="Note"><h3 class="NoteTipHead">
Note</h3>
<p><samp class="codeph">try_pop</samp> was called
<samp class="codeph">pop_if_present</samp> in Intel® TBB 2.1. Compile
with
<samp class="codeph">TBB_DEPRECATED=1</samp> to use the old name.
</p>
</div>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d39293e275 "><span class="keyword">void clear()</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d39293e278 ">
<p>Clears the queue. Afterwards
<samp class="codeph">size()==0</samp>.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d39293e275 "><span class="keyword">size_type unsafe_size()
const</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d39293e278 ">
<p><strong>Returns</strong>
</p>
<p>Number of items in the queue. If there are concurrent
modifications in flight, the value might not reflect the actual number of items
in the queue.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d39293e275 "><span class="keyword">bool empty() const</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d39293e278 ">
<p><strong>Returns</strong>:
<samp class="codeph">true</samp> if queue has no items; false otherwise.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d39293e275 "><span class="keyword">Alloc get_allocator()
const</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d39293e278 ">
<p><strong>Returns</strong>: Copy of allocator used to construct the
queue.
</p>
</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section"><h2 class="sectiontitle">Iterators</h2>
<p>A
<samp class="codeph">concurrent_queue</samp> provides limited iterator support
that is intended solely to allow programmers to inspect a queue during
debugging. It provides iterator and const_iterator types. Both follow the usual
STL conventions for forward iterators. The iteration order is from least
recently pushed to most recently pushed. Modifying a
<samp class="codeph">concurrent_queue</samp> invalidates any iterators that
reference it.
</p>
<div class="Note"><h3 class="NoteTipHead">
Caution</h3>
<p>The iterators are relatively slow. They should be used only for
debugging.
</p>
</div>
</div>
<div class="section"><h2 class="sectiontitle">Example</h2>
<p>The following program builds a queue with the integers 0..9, and then
dumps the queue to standard output. Its overall effect is to print 0 1 2 3 4 5
6 7 8 9.
</p>
<pre>#include "tbb/concurrent_queue.h"
#include <iostream>
using namespace std;
using namespace tbb;
int main() {
concurrent_queue<int> queue;
for( int i=0; i<10; ++i )
queue.push(i);
typedef concurrent_queue<int>::iterator iter;
for(iter i(queue.unsafe_begin()); i!=queue.unsafe_end(); ++i)
cout << *i << " ";
cout << endl;
return 0;
}
</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="d39293e517">Member
</th>
<th class="cellrowborder" valign="top" width="66.10169491525423%" id="d39293e520">Description
</th>
</tr>
</thead>
<tbody>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d39293e517 "><span class="keyword">iterator unsafe_begin()</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d39293e520 ">
<p><strong>Returns</strong>:
<samp class="codeph">iterator</samp> pointing to beginning of the queue.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d39293e517 "><span class="keyword">iterator unsafe_end()</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d39293e520 ">
<p><strong>Returns</strong>:
<samp class="codeph">iterator</samp> pointing to end of the queue.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d39293e517 "><span class="keyword">const_iterator unsafe_begin()
const</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d39293e520 ">
<p><strong>Returns</strong>:
<samp class="codeph">const_iterator</samp> with pointing to beginning of
the queue.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d39293e517 "><span class="keyword"></span><samp class="codeph">const_iterator</samp> unsafe_end()
const
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d39293e520 ">
<p><strong>Returns</strong>:
<samp class="codeph">const_iterator</samp> pointing to end of the queue.
</p>
</td>
</tr>
</tbody>
</table>
</div>
</div>
</div>
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