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Intel Threading Building Blocks by James Reinders

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Name

Template Class — Template class for queue with concurrent operations.concurrent_queue

Synopsis

#include "tbb/concurrent_queue.h"

template<typename T> class concurrent_queue;

Description

A concurrent_queue is a bounded data structure that permits multiple threads to concurrently push and pop items. Its behavior is first-in first-out in reference to any items pushed by a single thread and popped by a single thread. The default bounds are large enough to make the queue practically unbounded, subject to memory limitations on the target machine.

The interface is different from that of an STL std::queue because concurrent_queue is designed for concurrent operations. See Table 5-1 for the differences.

Table 5-1. std::queue versus tbb::concurrent_queue

Feature

STL std::queue

tbb::concurrent_queue

Access to front and back

front and back methods

Not present. They would be unsafe while concurrent operations are in progress.

size_type

Unsigned integral type

Signed integral type.

size( )

Returns the number of items in the queue

Returns the number of pushes minus the number of pops. Waiting push or pop operations are included in the difference. The size is negative if there are pops waiting for corresponding pushes.

Copy and pop item from queue q

x=q.front( )
q.pop( )

q.pop(x) waits for the object indefinitely. For an immediate return, use pop_if_present.

Copy and pop item unless queue q is empty

bool b=!q.empty( );
if(b) {
   x=q.front( );
    q.pop( );
}

q.pop_if_present(x) ...

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