Boost.Flyweight Tracking policies reference

Locking policies

Boost.Flyweight reference

Performance

Contents

• Preliminary concepts
• Tracking policies
• Header "boost/flyweight/tracking_tag.hpp" synopsis
  • Class template is_tracking
  • Class template tracking
• Header "boost/flyweight/refcounted_fwd.hpp" synopsis
• Header "boost/flyweight/refcounted.hpp" synopsis
  • Class refcounted
• Header "boost/flyweight/no_tracking_fwd.hpp" synopsis
• Header "boost/flyweight/no_tracking.hpp" synopsis
  • Class no_tracking

Preliminary concepts

A tracking policy helper provides access to some of the functionality of a factory so as to be used in the implementation of an associated Tracking Policy. In the following table, TrackingHelper is a tracking policy helper associated to a factory type Factory of elements of type Entry, h is a value of Factory::handle_type associated to a Factory f and check is a value of a Predicate type Checker with argument of type Factory::handle_type.

The execution of TrackingHelper::erase (including the invocation of check(h)) is done in a synchronized manner so as to prevent any other thread of execution from simultaneously accessing the factory's insertion or deletion facilities.

Tracking policies

A tracking policy defines the strategy to be followed by a flyweight instantiation when all the flyweight objects associated to a given value are destroyed. The tracking policy contributes some type information necessary for the definition of the flyweight internal factory.

A type Tracking is a tracking policy if:

• One of the following conditions is satisfied:
  1. is_tracking<Tracking>::type is boost::mpl::true_,
  2. Tracking is of the form tracking<Tracking'>.
• The expression Tracking::entry_type (or Tracking'::entry_type if (b) applies) is an MPL Lambda Expression that resolves, when invoked with different types (Value,Key) such that Value is Assignable and implicitly convertible to const Key&, to an Assignable type Entry implicitly convertible to both const Value& and const Key&.
• The expression Tracking::handle_type (or Tracking'::handle_type if (b) applies) is an MPL Lambda Expression; this expression, when invoked with types (InternalHandle,TrackingHelper), with InternalHandle being Assignable and providing the nothrow guarantee for copy and assignment, resolves to an Assignable type Handle which also provides the nothrow guarantee for copy and assignment and is constructible from and implicitly convertible to InternalHandle. TrackingHelper is an incomplete type at the time of invocation of Tracking::handle_type.

Header "boost/flyweight/tracking_tag.hpp" synopsis

namespace boost{

namespace flyweights{

struct tracking_marker;

template<typename T>
struct is_tracking

template<typename T>
struct tracking;

} // namespace boost::flyweights

} // namespace boost

Class template is_tracking

Unless specialized by the user, is_tracking<T>::type is boost::mpl::true_ if T is derived from tracking_marker, and it is boost::mpl::false_ otherwise.

Class template tracking

tracking<T> is a syntactic construct meant to indicate that T is a tracking policy without resorting to the mechanisms provided by the is_tracking class template.

Header "boost/flyweight/refcounted_fwd.hpp" synopsis

namespace boost{

namespace flyweights{

struct refcounted;

} // namespace boost::flyweights

} // namespace boost

refcounted_fwd.hpp forward declares the class refcounted.

Header "boost/flyweight/refcounted.hpp" synopsis

Class refcounted

Tracking Policy providing flyweight instantiations with reference counting semantics: when all the flyweight objects associated to a given value are destroyed, the corresponding entry is erased from flyweight's internal factory.

Header "boost/flyweight/no_tracking_fwd.hpp" synopsis

namespace boost{

namespace flyweights{

struct no_tracking;

} // namespace boost::flyweights

} // namespace boost

no_tracking_fwd.hpp forward declares the class no_tracking.

Header "boost/flyweight/no_tracking.hpp" synopsis

Class no_tracking

Null Tracking Policy: elements inserted into flyweight's internal factory are not erased until program termination.

Locking policies

Boost.Flyweight reference

Performance

Revised August 18th 2008

© Copyright 2006-2008 Joaquín M López Muñoz. Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)