001 // RoundRobinScheduler.java, created by wbeebee
002 // Copyright (C) 2002 Wes Beebee <wbeebee@mit.edu>
003 // Licensed under the terms of the GNU GPL; see COPYING for details.
004 package javax.realtime;
005
006 import java.util.List;
007 import java.util.ArrayList;
008 import java.util.NoSuchElementException;
009 import java.util.Iterator;
010
011 /** <code>RoundRobinScheduler</code> is an example of the dumbest possible
012 * scheduler that actually switches between threads.
013 * It's great for getting an idea of what's required in a scheduler.
014 */
015 public class RoundRobinScheduler extends Scheduler {
016 static RoundRobinScheduler instance = null;
017 RefList threadList = new RefList();
018 RefList disabledThreads = new RefList();
019 Iterator iterator = threadList.roundIterator();
020
021 protected RoundRobinScheduler() {
022 super();
023 setQuanta(10000); // Start switching after a specified number of milliseconds
024 }
025
026 /** Return an instance of a RoundRobinScheduler */
027 public static RoundRobinScheduler instance() {
028 if (instance == null) {
029 ImmortalMemory.instance().enter(new Runnable() {
030 public void run() {
031 instance = new RoundRobinScheduler();
032 }
033 });
034 }
035
036 return instance;
037 }
038
039 /** It is always feasible to add another thread to a RoundRobinScheduler. */
040 protected void addToFeasibility(Schedulable schedulable) {}
041
042 public void fireSchedulable(Schedulable schedulable) {
043 schedulable.run();
044 }
045
046 /** Used to determine the policy of the <code>Scheduler</code>. */
047 public String getPolicyName() {
048 return "Round robin";
049 }
050
051 /** It is always feasible to add another thread to a RoundRobinScheduler. */
052 public boolean isFeasible() {
053 return true;
054 }
055
056 /** It is always feasible to add another thread to a RoundRobinScheduler. */
057 protected boolean isFeasible(Schedulable s, ReleaseParameters rp) {
058 return true;
059 }
060
061 /** It is always feasible to add another thread to a RoundRobinScheduler. */
062 protected void removeFromFeasibility(Schedulable schedulable) {}
063
064 /** It is always feasible to add another thread to a RoundRobinScheduler. */
065 public boolean setIfFeasible(Schedulable schedulable,
066 ReleaseParameters release,
067 MemoryParameters memory) {
068 return true;
069 }
070
071 /** It is always feasible to add another thread to a RoundRobinScheduler. */
072 public boolean setIfFeasible(Schedulable schedulable,
073 ReleaseParameters release,
074 MemoryParameters memory,
075 ProcessingGroupParameters group) {
076 return true;
077 }
078
079 protected long chooseThread(long currentTime) {
080 setQuanta(10000); // Switch again after a specified number of milliseconds.
081 try {
082 return ((Long)iterator.next()).longValue();
083 } catch (NoSuchElementException e) {
084 return 0;
085 }
086 }
087
088 protected void addThread(RealtimeThread thread) {
089 threadList.add(thread.getUID());
090 }
091
092 protected void removeThread(RealtimeThread thread) {
093 threadList.remove(thread.getUID());
094 }
095
096 protected void addThread(long threadID) {
097 threadList.add(threadID);
098 }
099
100 protected void removeThread(long threadID) {
101 threadList.remove(threadID);
102 }
103
104 protected void disableThread(long threadID) {
105 threadList.remove(threadID);
106 disabledThreads.add(threadID);
107 }
108
109 protected void enableThread(long threadID) {
110 threadList.add(threadID);
111 disabledThreads.remove(threadID);
112 }
113
114 /** RoundRobinScheduler is too dumb to deal w/periods. */
115 protected void waitForNextPeriod(RealtimeThread rt) {
116 }
117
118 public String toString() {
119 return "["+threadList+","+disabledThreads+"]";
120 }
121 }