javax.realtime
Class Clock

java.lang.Object
  javax.realtime.Clock

Direct Known Subclasses:

HighResolutionClock, RealtimeClock

public abstract class Clock

extends Object

A clock advances from the past, through the present, into the future. It has a concept of now that can be queried through Clock.getTime(), and it can have events queued on it which will be fired when their appointed time is reached. There are many possible subclasses of clocks: real-time clocks, user time clocks, simulation time clocks. The idea of using multiple clocks may at first seem unusual but we allow it as a possible resource allocation strategy. Consider a real-time system where the natural events of the system have different tolerances for jitter (jitter refers to the distribution of the differences between when the events are actually raised or noticed by the software and when they should have really occurred according to time in the real-world). Assume the system functions properly if event A is noticed or raised within plus or minus 100 seconds of the actual time it should occur but event B must be noticed or raised within 100 microseconds of its actual time. Further assume, without loss of generality, that events A and B are periodic. An application could then create two instances of PeriodicTimer based on two clocks. The timer for event B should be based on a Clock which checks its queue at least every 100 microseconds but the timer for event A could be based on a Clock that checked its queue only every 100 seconds. This use of two clocks reduces the queue size of the accurate clock and thus queue management overhead is reduced.

Author:

Angelo Corsaro

Constructor Summary

Clock()

Method Summary

AbsoluteTime	absolute(RelativeTime time) Computes an absolute time that represent "this.getTime() + time".
void	absolute(RelativeTime time, AbsoluteTime destination) Computes an absolute time that represent "this.getTime() + time".
static Clock	getRealtimeClock() There is always one clock object available: a realtime clock that advances in sync with the external world> This is the default Clock.
abstract RelativeTime	getResolution() Return the resolution of the clock -- the interval between ticks.
AbsoluteTime	getTime() Return the current time in a freshly allocated object.
abstract void	getTime(AbsoluteTime time) Return the current time in an existing object.
RelativeTime	relative(AbsoluteTime time) Gets the RealtiveTime that represents the time between the now of this Clock, and the time represented by the AbsoluteTime.
void	relative(AbsoluteTime time, RelativeTime destination) Gets the RealtiveTime that represents the time between the now of this Clock, and the time represented by the AbsoluteTime.
abstract void	setResolution(RelativeTime resolution) Set the resolution of this.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Clock

public Clock()

Method Detail

getRealtimeClock

public static Clock getRealtimeClock()

There is always one clock object available: a realtime clock that advances in sync with the external world> This is the default Clock.

Returns:

an instance of the default Clock.

getResolution

public abstract RelativeTime getResolution()

Return the resolution of the clock -- the interval between ticks.

Returns:

A RelativeTime object representing the resolution of this.

setResolution

public abstract void setResolution(RelativeTime resolution)

Set the resolution of this. For some hardwhere clocks setting resolution impossible and if called on those nothing happens.

Implementation Note: If the requested resolution overceeds the one obtainable by the underlying hardware this method guarantees that the finest resolution possible is set.

Parameters:

resolution - The new resolution of this.

getTime

public AbsoluteTime getTime()

Return the current time in a freshly allocated object.

Returns:

An AbsoluteTime object representing the current time.

getTime

public abstract void getTime(AbsoluteTime time)

Return the current time in an existing object. The time represented by the given AbsoluteTime is changed some time between the invocation of the method and the return of the method.

Parameters:

time - The AbsoluteTime object which will have its time changed.

relative

public RelativeTime relative(AbsoluteTime time)

Gets the RealtiveTime that represents the time between the now of this Clock, and the time represented by the AbsoluteTime.

Parameters:

time - an AbsoluteTime

Returns:

the resulting RelativeTime.

relative

public void relative(AbsoluteTime time,
                     RelativeTime destination)

Gets the RealtiveTime that represents the time between the now of this Clock, and the time represented by the AbsoluteTime.

Parameters:

time - an AbsoluteTime

destination - the destination for the resulting RelativeTime.

absolute

public AbsoluteTime absolute(RelativeTime time)

Computes an absolute time that represent "this.getTime() + time".

Parameters:

time - the RelativeTime value

Returns:

the resulting AbsoluteTime value

absolute

public void absolute(RelativeTime time,
                     AbsoluteTime destination)

Computes an absolute time that represent "this.getTime() + time".

Parameters:

time - the RelativeTime value

destination - the AbsoluteTime that will contain the result