001 // AperiodicParameters.java, created by cata
002 // Copyright (C) 2001 Catalin Francu <cata@mit.edu>
003 // Licensed under the terms of the GNU GPL; see COPYING for details.
004
005 package javax.realtime;
006
007 import java.util.LinkedList;
008 import java.util.Iterator;
009
010 /** The release parameter object characterizes a schedulable object that may become
011 * active at atny time. When a reference to a <code>AperiodicParameters</code>
012 * object is given as a parameter to a constructor the
013 * <code>AperiodicParameters</code> object becomes bound to the object being created.
014 * Changed to the values in the <code>AperiodicParameters</code> object affect the
015 * constructed object. If given to more than one constructor then changes to the values
016 * in the <code>AperiodicParameters</code> object affect <i>all</i> of the associated
017 * objects. Note that this is a one-to-many relationship and <i>not</i> a many-to-many.
018 * <p>
019 * <b>Caution:</b> This class is explicitly unsafe in multithreaded situations when it
020 * is being changed. No synchronization is done. It is assumed that users of this class
021 * who are mutating instances will be doing their own synchronization at a higher level.
022 */
023 public class AperiodicParameters extends ReleaseParameters {
024 LinkedList schList = new LinkedList();
025
026 /** Create an <code>AperiodicParameters</code> object.
027 *
028 * @param cost Processing time per invocation. On implementations which can measure
029 * the amount of time a schedulable object is executed, this value is the
030 * maximum amount of time a schedulable object receives. On implementations
031 * which cannot measure execution time, this value is used as a hint to the
032 * feasibility algorithm. On such systems it is not possible to determine
033 * when any particular object exceeds cost. Equivalent to
034 * <code>RelativeTime(0, 0)</code> if null.
035 * @param deadline The latest permissible completion time measured from the release
036 * time of the associated invocation of the schedulable object. Not
037 * used in feasibility analysis for minimum implementation. If null,
038 * the deadline will be <code>RelativeTime(Long.MAX_VALUE, 999999)</code>.
039 * @param overrunHandler This handler is invoked if an invocation of the schedulable
040 * object exceeds cost. Not required for minimum implementation.
041 * If null, nothing happens on the overrun condition.
042 * @param missHandler This handler is invoked if the <code>run()</code> method of the
043 * schedulable object is still executing after the deadline has passed.
044 * Although minimum implementations do not consider deadlines in
045 * feasibility calculations, they must recognize variable deadlines
046 * and invoke the miss handler as appropriate. If null, nothing
047 * happens on the miss deadline condition.
048 */
049 public AperiodicParameters(RelativeTime cost, RelativeTime deadline,
050 AsyncEventHandler overrunHandler,
051 AsyncEventHandler missHandler) {
052 super(cost,
053 (deadline == null) ? new RelativeTime(Long.MAX_VALUE, 999999) :
054 deadline,
055 overrunHandler, missHandler);
056 }
057
058 /** This method appears in many classes in the RTSJ and with various parameters.
059 * The parameters are either new scheduling characteristics for an instance
060 * <code>Schedulable</code> or an instance of <code>Schedulable</code>. The
061 * method first performs a feasibility analysis using the new scheduling
062 * characteristics as replacements for the matching scheduling characteristics
063 * of either <code>this</code> or the given instance of <code>Schedulable</code>.
064 * If the resulting system is feasible the method replaces the current scheduling
065 * characteristics, of either <code>this</code> or the given instance of
066 * <code>Schedulable</code> as appropriate, with the new scheduling characteristics.
067 *
068 * @param cost The proposed cost.
069 * @param deadline The proposed deadline.
070 * @return True, if the resulting system is feasible and the changes are made.
071 * False, if the resulting system is not feasible and no changes are made.
072 */
073 public boolean setIfFeasible(RelativeTime cost,
074 RelativeTime deadline) {
075 boolean b = true;
076 for (Iterator it = schList.iterator(); it.hasNext(); ) {
077 Schedulable sch = (Schedulable)it.next();
078 Scheduler sched = sch.getScheduler();
079 if (!sched.isFeasible(sch, new AperiodicParameters(cost, deadline, overrunHandler, missHandler))) {
080 b = false;
081 break;
082 }
083 }
084
085 if (b) {
086 setCost(cost);
087 setDeadline(deadline);
088 }
089 return b;
090 }
091
092 /** Informs <code>this</code> that there is one more instance of <code>Schedulable</code>
093 * that uses <code>this</code> as its <code>ReleaseParameters</code>.
094 */
095 public boolean bindSchedulable(Schedulable sch) {
096 return schList.add(sch);
097 }
098
099 /** Informs <code>this</code> that <code>Schedulable sch</code>
100 * that uses <code>this</code> as its <code>ReleaseParameters</code>.
101 */
102 public boolean unbindSchedulable(Schedulable sch) {
103 return schList.remove(sch);
104 }
105 }