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 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 AsyncEventHandler with a ReleaseParameters54 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 AsyncEvent181 bound to the instance of AsyncEventHandler.

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.

Author:

Angelo Corsaro

Field Summary

static String	arrivalTimeQueueOverflowExcpt 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 thearrival time is a result of a happening to which the instance of AsyncEventHandler is bound then the arrival time is ignored.
static 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 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 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.
protected int	intialQueueLength
protected RelativeTime	minInterarrival
protected String	mitPolicy
static String	mitViolationExcept If an arrival time for any instance of Schedulable41 which has this as its instance of ReleaseParameters occurs at a time less then the mini-mum interarrival time defined here then the fire() method shall throw MITViolationException.
static String	mitViolationIgnore If an arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters occurs at a time less then the mini-mum interarrival time defined here then the new arrival time is ignored.
static String	mitViolationReplace If an arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters occurs at a time less then the mini-mum interarrival time defined here then, if necessary, the previous arrival time may be overwritten with the new arrival time.
static String	mitViolationSave If an arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters occurs at a time less then the mini-mum interarrival time defined here then the new arrival time is added to the queue of arrival times.
protected String	queuePolicy

Fields inherited from class javax.realtime.ReleaseParameters

cost, deadline, missHandler, overrunHandler

Constructor Summary

SporadicParameters(RelativeTime minInterarrival, RelativeTime cost, RelativeTime deadline, AsyncEventHandler overrunHandler, AsyncEventHandler missHandler)
Creates a new SporadicParameters instance.

Method Summary

String	getArrivalTimeQueueOverflowBehavior() Get the behavior of the arrival time queue in the event of an overflow.
int	getInitialArrivalTimeQueueLength() Get the initial number of elements the arrival time queue can hold.
void	getInitialArrivalTimeQueueLength(int initial) Set the initial number of elements the arrival time queue can hold without lengthening the queue.
RelativeTime	getMinimumInterarrival() Get the minimum interarrival time.
String	getMitViolationBehavior() Get the arrival time queue behavior in the event of a minimum interarrival time violation.
void	setArrivalTimeQueueOverflowBehavior(String behavior) Set 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) Returns true if, after considering the values of the parameters, the task set would still be feasible.
void	setInitialArrivalTimeQueueLength(String behavior) Set the behavior of the arrival time queue in the case where the new arrival time is closer to the previous arrival time than the minimum interarrival time given in this.
void	setMinimumInterarrival(RelativeTime mit) Set the minimum interarrival time.

Methods inherited from class javax.realtime.AperiodicParameters

setIfFeasible

Methods inherited from class javax.realtime.ReleaseParameters

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

Methods inherited from class java.lang.Object

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

Field Detail

minInterarrival

protected RelativeTime minInterarrival

queuePolicy

protected String queuePolicy

mitPolicy

protected String mitPolicy

intialQueueLength

protected int intialQueueLength

arrivalTimeQueueOverflowExcpt

public static final String arrivalTimeQueueOverflowExcpt

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 thearrival time is a result of a happening to which the instance of AsyncEventHandler is bound then the arrival time is ignored.

See Also:

Constant Field Values

arrivalTimeQueueOverflowIgnore

public static final 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.

See Also:

Constant Field Values

arrivalTimeQueueOverflowReplace

public static final 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.

See Also:

Constant Field Values

arrivalTimeQueueOverflowSave

public static final 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.

See Also:

Constant Field Values

mitViolationExcept

public static final String mitViolationExcept

If an arrival time for any instance of Schedulable41 which has this as its instance of ReleaseParameters occurs at a time less then the mini-mum interarrival time defined here then the fire() method shall throw MITViolationException. If the arrival time is a result of a happen-ing to which the instance of AsyncEventHandler is bound then the arrival time is ignored.

See Also:

Constant Field Values

mitViolationIgnore

public static final String mitViolationIgnore

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

See Also:

Constant Field Values

mitViolationReplace

public static final String mitViolationReplace

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

See Also:

Constant Field Values

mitViolationSave

public static final String mitViolationSave

If an arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters occurs at a time less then the mini-mum interarrival time defined here then the new arrival time is added to the queue of arrival times. However, the new time is adjusted so that the differ-ence between it and the previous time is equal to the minimum interarrival time.

See Also:

Constant Field Values

Constructor Detail

SporadicParameters

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

Creates a new SporadicParameters instance.

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 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.

Implementation Note: By default the Queue Overflow, and the Minimum Interarrival Time Violation are set to save.

Method Detail

getArrivalTimeQueueOverflowBehavior

public String getArrivalTimeQueueOverflowBehavior()

Get the behavior of the arrival time queue in the event of an overflow.

Returns:

a String representing the behaviour currently set.

setArrivalTimeQueueOverflowBehavior

public void setArrivalTimeQueueOverflowBehavior(String behavior)

Set 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.

Parameters:

behavior - a string representing the desired behavior.

getInitialArrivalTimeQueueLength

public int getInitialArrivalTimeQueueLength()

Get the initial number of elements the arrival time queue can hold.

Returns:

the initial number of elements the arrival time queue can hold.

getInitialArrivalTimeQueueLength

public void getInitialArrivalTimeQueueLength(int initial)

Set the initial number of elements the arrival time queue can hold without lengthening the queue.

Parameters:

initial - the initial lenght of the queue.

getMinimumInterarrival

public RelativeTime getMinimumInterarrival()

Get the minimum interarrival time.

Returns:

the minimum interarrival time.

setMinimumInterarrival

public void setMinimumInterarrival(RelativeTime mit)

Set the minimum interarrival time.

Parameters:

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

getMitViolationBehavior

public String getMitViolationBehavior()

Get the arrival time queue behavior in the event of a minimum interarrival time violation.

Returns:

the arrival time queue behavior.

setInitialArrivalTimeQueueLength

public void setInitialArrivalTimeQueueLength(String behavior)

Set the behavior of the arrival time queue in the case where the new arrival time is closer to the previous arrival time than the minimum interarrival time given in this.

Parameters:

behavior - a string representin the desired behaviour.

setIfFeasible

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

Returns true if, after considering the values of the parameters, the task set would still be feasible. In this case the values of the parameters are changed. Returns false if, after considering the values of the parameters, the task set would not be feasible. In this case the values of the parameters are not changed.

Parameters:

interarrival - 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 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.

Returns:

True if the new parameters can be changed while keeping the schedule feasible.