Intel Threading Building Blocks

Name

parallel_while Template Class — Template class that processes work items.

Synopsis

#include "tbb/parallel_while.h"

template<typename Body> class parallel_while;

Description

A parallel_while<Body> performs parallel iteration over items. The processing to be performed on each item is defined by a function object of type Body. The items are specified in two ways:

• An initial stream of items

• Additional items that are added while the stream is being processed

Table 4-1 shows the requirements on the stream and body.

Table 4-1. Requirements for parallel_while stream and body

Pseudosignature	Semantics
boolS::pop_if_present(B::argument_type&item)	Get next stream item. parallel_while does not concurrently invoke the method on the same object.
B::operator()(B::argument_type&item) const	Process item. parallel_while may concurrently invoke the operator for the same object but a different item.
B::argument_type()	Default constructor.
B::argument_type(constB::argument_type&)	Copy constructor.
~B::argument_type()	Destructor.

For example, a unary function object, as defined in Section 20.3 of the C++ standard, models the requirements for B. A concurrent_queue models the requirements for S.

Tip

To achieve speedup, the grain size of B::operator() needs to be on the order of 10,000 instructions to execute. Otherwise, the internal over-heads of parallel_while swamp the useful work. The parallelism in parallel_while is not scalable if all the items come from the input stream. To achieve ...