javax.realtime
Class SporadicParameters

java.lang.Object
  javax.realtime.ReleaseParameters
      javax.realtime.AperiodicParameters
          javax.realtime.SporadicParameters

public class SporadicParameters

extends AperiodicParameters

A notice to the scheduler that the associated schedulable object's run() method will be released aperiodically but with a minimum time between releases. When a reference to a SporadicParameters object is given as a parameter to a constructor, the SporadicParameters object becomes bound to the object being created. Changes to the values in the SporadicParameters object affect the constructed object. If given to more than one constructor, then changes to the values in the SporadicParameters object will affect all of the associated objects. Note that this is a one-to-many relationship and not a many-to-many.

Caution: This class is explicitly unsafe in multithreaded situations when it is being changed. No synchronization is done. It is assumed that users of this class who are mutating instances will be doing their own synchronization at a higher level.

Correct initiation of the deadline miss and cost overrun handlers requires that the underlying system know the arrival time of each sporadic task. For an instance of RealtimeThread the arrival time is the time at which the start() is invoked. For other instances of Schedulable it may be required for the implementation to save the arrival times. For instances of AsynchEventHandler with a ReleaseParameters type of SporadicParameters the implementation must maintain a queue of monotonically increasing arrival times which correspond to the execution of the fire() method of the instance of AsynchEvent bound to the instance of AsynchEventHandler.

This class allows the application to specify one of four possible behaviors that indicate what to do if an arrival occurs that is closer in time to the previous arrival than the value given in this class as minimum interarrival time, what to do if, for any reason, the queue overflows, and the initial size of the queue.

Field Summary

static java.lang.String	arrivalTimeQueueOverflowExcept If an arrival time occurs and should be queued but the queue already holds a number of times equal to the initial queue length defined by this then the fire() method shall throw a ResourceLimitError.
static java.lang.String	arrivalTimeQueueOverflowIgnore If an arrival time occurs and should be queued but the queue already holds a number of times equal to the initial queue length defined by this then the arrival time is ignored.
static java.lang.String	arrivalTimeQueueOverflowReplace If an arrival time occurs and should be queued but the queue already holds a number of times equal to the initial queue length defined by this then the previous arrival time is overwritten by the new arrival time.
static java.lang.String	arrivalTimeQueueOverflowSave If an arrival time occurs and should be queued but the queue already holds a number of times equal to the initial queue length defined by this then the queue is lengthened and the arrival time is saved.
static java.lang.String	mitViolationExcept If an arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters occurs at a time less than the minimum interarrival time defined here then the fire() method shall throw MITViolationException.
static java.lang.String	mitViolationIgnore If an arrival time for any instance of Schedulable which as this as its instance of ReleaseParameters occurs at a time less than the minimum interarrival time defined here then the new arrival time is ignored.
static java.lang.String	mitViolationReplace If an arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters occurs at a time less than the minimum interarrival time defined here then, if necessary, the previous arrival time may be overwritten with the new arrival time.
static java.lang.String	mitViolationSave If an arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters occurs at a time less than the minimum interarrival time defined here then the new arrival time is adjusted so that the difference between it and the previous time is equal to the minimum interarrival time.

Fields inherited from class javax.realtime.ReleaseParameters

cost, deadline, missHandler, overrunHandler

Constructor Summary

SporadicParameters(RelativeTime minInterval, RelativeTime cost)
Constructor.

SporadicParameters(RelativeTime minInterarrival, RelativeTime cost, RelativeTime deadline, AsyncEventHandler overrunHandler, AsyncEventHandler missHandler)
Create a SporadicParameters object.

Method Summary

int	getArrivalTimeQueueLength()
RelativeTime	getMinimumInterarrival()
java.lang.String	getMitViolationBehavior()
void	setArrivalTimeQueueOverflowBehavior(java.lang.String behavior) Sets the behavior of the arrival time queue in the case where the insertion of a new element would make the queue size greater than the initial size given in this.
boolean	setIfFeasible(RelativeTime interarrival, RelativeTime cost, RelativeTime deadline)
void	setInitialArrivalTimeQueueLength(int initial) Sets the initial number of elements the arrival time queue can hold without lengthening the queue.
void	setMinimumInterarrival(RelativeTime minimum)
void	setMitViolationBehavior(java.lang.String behavior)

Methods inherited from class javax.realtime.AperiodicParameters

getArrivalTimeQueueOverflowBehavior, getInitialArrivalTimeQueueLength, setDeadline, setIfFeasible

Methods inherited from class javax.realtime.ReleaseParameters

getCost, getCostOverrunHandler, getDeadline, getDeadlineMissHandler, setCost, setCostOverrunHandler, setDeadlineMissHandler

Methods inherited from class java.lang.Object

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

Field Detail

arrivalTimeQueueOverflowExcept

public static final java.lang.String arrivalTimeQueueOverflowExcept

If an arrival time occurs and should be queued but the queue already holds a number of times equal to the initial queue length defined by this then the fire() method shall throw a ResourceLimitError. If the arrival time is a result of a happening to which the instance of AsyncEventHandler is bound then the arrival time is ignored.

arrivalTimeQueueOverflowIgnore

public static final java.lang.String arrivalTimeQueueOverflowIgnore

If an arrival time occurs and should be queued but the queue already holds a number of times equal to the initial queue length defined by this then the arrival time is ignored.

arrivalTimeQueueOverflowReplace

public static final java.lang.String arrivalTimeQueueOverflowReplace

If an arrival time occurs and should be queued but the queue already holds a number of times equal to the initial queue length defined by this then the previous arrival time is overwritten by the new arrival time. However, the new time is adjusted so that the difference between it and the previous time is equal to the minimum interarrival time.

arrivalTimeQueueOverflowSave

public static final java.lang.String arrivalTimeQueueOverflowSave

If an arrival time occurs and should be queued but the queue already holds a number of times equal to the initial queue length defined by this then the queue is lengthened and the arrival time is saved.

mitViolationExcept

public static final java.lang.String mitViolationExcept

If an arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters occurs at a time less than the minimum interarrival time defined here then the fire() method shall throw MITViolationException. If the arrival time is a result of a happening to which the instance of AsyncEventHandler is bound then the arrival time is ignored.

mitViolationIgnore

public static final java.lang.String mitViolationIgnore

If an arrival time for any instance of Schedulable which as this as its instance of ReleaseParameters occurs at a time less than the minimum interarrival time defined here then the new arrival time is ignored.

mitViolationReplace

public static final java.lang.String mitViolationReplace

If an arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters occurs at a time less than the minimum interarrival time defined here then, if necessary, the previous arrival time may be overwritten with the new arrival time.

mitViolationSave

public static final java.lang.String mitViolationSave

If an arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters occurs at a time less than the minimum interarrival time defined here then the new arrival time is adjusted so that the difference between it and the previous time is equal to the minimum interarrival time.

Constructor Detail

SporadicParameters

public SporadicParameters(RelativeTime minInterarrival,
                          RelativeTime cost,
                          RelativeTime deadline,
                          AsyncEventHandler overrunHandler,
                          AsyncEventHandler missHandler)

Create a SporadicParameters object.

Parameters:

minInterarrival - The release times of the schedulable object will occur no closer than this interval. Must be greater than zero when entering feasibility analysis.

cost - Processing time per minimum interarrival interval. On implementations which can measure the amount of time a schedulable object is executed, this value is the maximum amount of time a schedulable object receives per interval. On implementations which cannot measure execution time, this value is used as a hint to the feasibility algorithm. On such systems it is not possible to determine when any particular object exceeds cost. Equivalent to RelativeTime(0,0) if null.

deadline - The latest permissible completion time measured from the release time of the associated invocation of the schedulable object. For a minimum implementation for purposes of feasibility analysis, the deadline is set equal to the minimum interarrival interval. Other implementations may use this parameter to compute execution eligibility. If null, deadline will equal the minimum interarrival time.

overrunHandler - This handler is invoked if an invocation of the schedulable object exceeds cost. Not required for minimum implementation. If null, nothing happens on the overrun condition.

missHandler - This handler is invoked if the run() method of the schedulable object is still executing after the deadline has passed. Although minimum implementations do not consider deadlines in feasibility calculations, they must recognize variable deadlines and invoke the miss handler as appropriate. If null, nothing happens on the miss deadline condition.

SporadicParameters

public SporadicParameters(RelativeTime minInterval,
                          RelativeTime cost)

Constructor.

Parameters:

minInterval -

cost -

Method Detail

getMinimumInterarrival

public RelativeTime getMinimumInterarrival()

Returns:

the minimum interarrival time of this object.

getMitViolationBehavior

public java.lang.String getMitViolationBehavior()

Returns:

the MIT violation behavior of this object.

setArrivalTimeQueueOverflowBehavior

public void setArrivalTimeQueueOverflowBehavior(java.lang.String behavior)

Description copied from class: AperiodicParameters

Sets the behavior of the arrival time queue in the case where the insertion of a new element would make the queue size greater than the initial size given in this.

Overrides:

setArrivalTimeQueueOverflowBehavior in class AperiodicParameters

Parameters:

behavior - the arrival time queue overflow behavior of this object

setIfFeasible

public boolean setIfFeasible(RelativeTime interarrival,
                             RelativeTime cost,
                             RelativeTime deadline)

Parameters:

interarrival -

cost -

deadline -

Returns:

true if the resulting system is feasible.

setInitialArrivalTimeQueueLength

public void setInitialArrivalTimeQueueLength(int initial)

Description copied from class: AperiodicParameters

Sets the initial number of elements the arrival time queue can hold without lengthening the queue. The initial length of an arrival queue is set when the SO using the queue is constructed, after that time changes in the initial queue length are ignored.

Overrides:

setInitialArrivalTimeQueueLength in class AperiodicParameters

Parameters:

initial -

setMinimumInterarrival

public void setMinimumInterarrival(RelativeTime minimum)

Parameters:

minimum -

setMitViolationBehavior

public void setMitViolationBehavior(java.lang.String behavior)

Parameters:

behavior -

getArrivalTimeQueueLength

public int getArrivalTimeQueueLength()

Returns:

the arrival time queue length of this object