A class defining a common interface for counters. More...

#include <arc/Counter.h>

Inheritance diagram for Arc::Counter:

Public Member Functions
virtual	~Counter ()
	The destructor. More...

virtual int	getLimit ()=0
	Returns the current limit of the counter. More...

virtual int	setLimit (int newLimit)=0
	Sets the limit of the counter. More...

virtual int	changeLimit (int amount)=0
	Changes the limit of the counter. More...

virtual int	getExcess ()=0
	Returns the excess limit of the counter. More...

virtual int	setExcess (int newExcess)=0
	Sets the excess limit of the counter. More...

virtual int	changeExcess (int amount)=0
	Changes the excess limit of the counter. More...

virtual int	getValue ()=0
	Returns the current value of the counter. More...

virtual CounterTicket	reserve (int amount=1, Glib::TimeVal duration=ETERNAL, bool prioritized=false, Glib::TimeVal timeOut=ETERNAL)=0
	Makes a reservation from the counter. More...

Protected Types
typedef unsigned long long int	IDType
	A typedef of identification numbers for reservation. More...

Protected Member Functions
	Counter ()
	Default constructor. More...

virtual void	cancel (IDType reservationID)=0
	Cancellation of a reservation. More...

virtual void	extend (IDType &reservationID, Glib::TimeVal &expiryTime, Glib::TimeVal duration=ETERNAL)=0
	Extension of a reservation. More...

Glib::TimeVal	getCurrentTime ()
	Get the current time. More...

Glib::TimeVal	getExpiryTime (Glib::TimeVal duration)
	Computes an expiry time. More...

CounterTicket	getCounterTicket (Counter::IDType reservationID, Glib::TimeVal expiryTime, Counter *counter)
	A "relay method" for a constructor of the CounterTicket class. More...

ExpirationReminder	getExpirationReminder (Glib::TimeVal expTime, Counter::IDType resID)
	A "relay method" for the constructor of ExpirationReminder. More...

Friends
class	CounterTicket
	The CounterTicket class needs to be a friend. More...

class	ExpirationReminder
	The ExpirationReminder class needs to be a friend. More...

Detailed Description

A class defining a common interface for counters.

This class defines a common interface for counters as well as some common functionality.

The purpose of a counter is to provide housekeeping some resource such as e.g. disk space, memory or network bandwidth. The counter itself will not be aware of what kind of resource it limits the use of. Neither will it be aware of what unit is being used to measure that resource. Counters are thus very similar to semaphores. Furthermore, counters are designed to handle concurrent operations from multiple threads/processes in a consistent manner.

Every counter has a limit, an excess limit and a value. The limit is a number that specify how many units are available for reservation. The value is the number of units that are currently available for reservation, i.e. has not already been reserved. The excess limit specify how many extra units can be reserved for high priority needs even if there are no normal units available for reservation. The excess limit is similar to the credit limit of e.g. a VISA card.

The users of the resource must thus first call the counter in order to make a reservation of an appropriate amount of the resource, then allocate and use the resource and finally call the counter again to cancel the reservation.

Typical usage is:

// Declare a counter. Replace XYZ by some appropriate kind of
// counter and provide required parameters. Unit is MB.
XYZCounter memory(...);
...
// Make a reservation of memory for 2000000 doubles.
CounterTicket tick = memory.reserve(2*sizeof(double));
// Use the memory.
double* A=new double[2000000];
doSomething(A);
delete[] A;
// Cancel the reservation.
tick.cancel();

There are also alternative ways to make reservations, including self-expiring reservations, prioritized reservations and reservations that fail if they cannot be made fast enough.

For self expiring reservations, a duration is provided in the reserve call:

tick = memory.reserve(2*sizeof(double), Glib::TimeVal(1,0));

A self-expiring reservation can be cancelled explicitly before it expires, but if it is not cancelled it will expire automatically when the duration has passed. The default value for the duration is ETERNAL, which means that the reservation will not be cancelled automatically.

Prioritized reservations may use the excess limit and succeed immediately even if there are no normal units available for reservation. The value of the counter will in this case become negative. A prioritized reservation looks like this:

tick = memory.reserve(2*sizeof(double), Glib::TimeVal(1,0), true);

Finally, a time out option can be provided for a reservation. If some task should be performed within two seconds or not at all, the reservation can look like this:

tick = memory.reserve(2*sizeof(double), Glib::TimeVal(1,0),
                     true, Glib::TimeVal(2,0));
if (tick.isValid())
 doSomething(...);

Member Typedef Documentation

◆ IDType

typedef unsigned long long int Arc::Counter::IDType

protected

A typedef of identification numbers for reservation.

This is a type that is used as identification numbers (keys) for referencing of reservations. It is used internally in counters for book keeping of reservations as well as in the CounterTicket class in order to be able to cancel and extend reservations.

Constructor & Destructor Documentation

◆ Counter()

Arc::Counter::Counter ( )

protected

Default constructor.

This is the default constructor. Since Counter is an abstract class, it should only be used by subclasses. Therefore it is protected. Furthermore, since the Counter class has no attributes, nothing needs to be initialized and thus this constructor is empty.

◆ ~Counter()

virtual Arc::Counter::~Counter ( )

virtual

The destructor.

This is the destructor of the Counter class. Since the Counter class has no attributes, nothing needs to be cleaned up and thus the destructor is empty.

Member Function Documentation

◆ cancel()

virtual void Arc::Counter::cancel ( IDType reservationID )

protectedpure virtual

Cancellation of a reservation.

This method cancels a reservation. It is called by the CounterTicket that corresponds to the reservation.

Parameters

reservationID The identity number (key) of the reservation to cancel.

Implemented in Arc::IntraProcessCounter.

◆ changeExcess()

virtual int Arc::Counter::changeExcess ( int amount )

pure virtual

Changes the excess limit of the counter.

Changes the excess limit of the counter by adding a certain amount to the current excess limit.

Parameters

amount The amount by which to change the excess limit.

Returns: The new excess limit.

Implemented in Arc::IntraProcessCounter.

◆ changeLimit()

virtual int Arc::Counter::changeLimit ( int amount )

pure virtual

Changes the limit of the counter.

Changes the limit of the counter by adding a certain amount to the current limit.

Parameters

amount The amount by which to change the limit.

Returns: The new limit.

Implemented in Arc::IntraProcessCounter.

◆ extend()

virtual void Arc::Counter::extend	(	IDType &	reservationID,
		Glib::TimeVal &	expiryTime,
		Glib::TimeVal	duration = `ETERNAL`
	)

protectedpure virtual

Extension of a reservation.

This method extends a reservation. It is called by the CounterTicket that corresponds to the reservation.

Parameters

reservationID	Used for input as well as output. Contains the identification number of the original reservation on entry and the new identification number of the extended reservation on exit.
expiryTime	Used for input as well as output. Contains the expiry time of the original reservation on entry and the new expiry time of the extended reservation on exit.
duration	The time by which to extend the reservation. The new expiration time is computed based on the current time, NOT the previous expiration time.

Implemented in Arc::IntraProcessCounter.

◆ getCounterTicket()

CounterTicket Arc::Counter::getCounterTicket	(	Counter::IDType	reservationID,
		Glib::TimeVal	expiryTime,
		Counter *	counter
	)

protected

A "relay method" for a constructor of the CounterTicket class.

This method acts as a relay for one of the constructors of the CounterTicket class. That constructor is private, but needs to be accessible from the subclasses of Counter (but not from anywhere else). In order not to have to declare every possible subclass of Counter as a friend of CounterTicket, only the base class Counter is a friend and its subclasses access the constructor through this method. (If C++ had supported "package access", as Java does, this trick would not have been necessary.)

Parameters

reservationID	The identity number of the reservation corresponding to the CounterTicket.
expiryTime	the expiry time of the reservation corresponding to the CounterTicket.
counter	The Counter from which the reservation has been made.

Returns: The counter ticket that has been created.

◆ getCurrentTime()

Glib::TimeVal Arc::Counter::getCurrentTime ( )

protected

Get the current time.

Returns the current time. An "adapter method" for the assign_current_time() method in the Glib::TimeVal class. return The current time.

◆ getExcess()

virtual int Arc::Counter::getExcess ( )

pure virtual

Returns the excess limit of the counter.

Returns the excess limit of the counter, i.e. by how much the usual limit may be exceeded by prioritized reservations.

Returns: The excess limit.

Implemented in Arc::IntraProcessCounter.

◆ getExpirationReminder()

ExpirationReminder Arc::Counter::getExpirationReminder	(	Glib::TimeVal	expTime,
		Counter::IDType	resID
	)

protected

A "relay method" for the constructor of ExpirationReminder.

This method acts as a relay for one of the constructors of the ExpirationReminder class. That constructor is private, but needs to be accessible from the subclasses of Counter (but not from anywhere else). In order not to have to declare every possible subclass of Counter as a friend of ExpirationReminder, only the base class Counter is a friend and its subclasses access the constructor through this method. (If C++ had supported "package access", as Java does, this trick would not have been necessary.)

Parameters

expTime	the expiry time of the reservation corresponding to the ExpirationReminder.
resID	The identity number of the reservation corresponding to the ExpirationReminder.

Returns: The ExpirationReminder that has been created.

◆ getExpiryTime()

Glib::TimeVal Arc::Counter::getExpiryTime ( Glib::TimeVal duration )

protected

Computes an expiry time.

This method computes an expiry time by adding a duration to the current time.

Parameters

duration The duration.

Returns: The expiry time.

◆ getLimit()

virtual int Arc::Counter::getLimit ( )

pure virtual

Returns the current limit of the counter.

This method returns the current limit of the counter, i.e. how many units can be reserved simultaneously by different threads without claiming high priority.

Returns: The current limit of the counter.

Implemented in Arc::IntraProcessCounter.

◆ getValue()

virtual int Arc::Counter::getValue ( )

pure virtual

Returns the current value of the counter.

Returns the current value of the counter, i.e. the number of unreserved units. Initially, the value is equal to the limit of the counter. When a reservation is made, the the value is decreased. Normally, the value should never be negative, but this may happen if there are prioritized reservations. It can also happen if the limit is decreased after some reservations have been made, since reservations are never revoked.

Returns: The current value of the counter.

Implemented in Arc::IntraProcessCounter.

◆ reserve()

virtual CounterTicket Arc::Counter::reserve	(	int	amount = `1`,
		Glib::TimeVal	duration = `ETERNAL`,
		bool	prioritized = `false`,
		Glib::TimeVal	timeOut = `ETERNAL`
	)

pure virtual

Makes a reservation from the counter.

This method makes a reservation from the counter. If the current value of the counter is too low to allow for the reservation, the method blocks until the reservation is possible or times out.

Parameters

amount	The amount to reserve, default value is 1.
duration	The duration of a self expiring reservation, default is that it lasts forever.
prioritized	Whether this reservation is prioritized and thus allowed to use the excess limit.
timeOut	The maximum time to block if the value of the counter is too low, default is to allow "eternal" blocking.

Returns: A CounterTicket that can be queried about the status of the reservation as well as for cancellations and extensions.

Implemented in Arc::IntraProcessCounter.

◆ setExcess()

virtual int Arc::Counter::setExcess ( int newExcess )

pure virtual

Sets the excess limit of the counter.

This method sets a new excess limit for the counter.

Parameters

newExcess The new excess limit, an absolute number.

Returns: The new excess limit.

Implemented in Arc::IntraProcessCounter.

◆ setLimit()

virtual int Arc::Counter::setLimit ( int newLimit )

pure virtual

Sets the limit of the counter.

This method sets a new limit for the counter.

Parameters

newLimit The new limit, an absolute number.

Returns: The new limit.

Implemented in Arc::IntraProcessCounter.

Friends And Related Function Documentation

◆ CounterTicket

friend class CounterTicket

friend

The CounterTicket class needs to be a friend.

◆ ExpirationReminder

friend class ExpirationReminder

friend

The ExpirationReminder class needs to be a friend.

The documentation for this class was generated from the following file:

Counter.h

Public Member Functions

Protected Types

Protected Member Functions

Friends

Detailed Description

Member Typedef Documentation

◆ IDType

Constructor & Destructor Documentation

◆ Counter()

◆ ~Counter()

Member Function Documentation

◆ cancel()

◆ changeExcess()

◆ changeLimit()

◆ extend()

◆ getCounterTicket()

◆ getCurrentTime()

◆ getExcess()

◆ getExpirationReminder()

◆ getExpiryTime()

◆ getLimit()

◆ getValue()

◆ reserve()

◆ setExcess()

◆ setLimit()

Friends And Related Function Documentation

◆ CounterTicket

◆ ExpirationReminder