Thread-safety improvements

- You should now be able to safely add an event to the PeriodicScheduler
from within a scheduled event
- You should be able to share Preference and PreferencesSet objects
across multiple threads.  Note that onPreferencesUpdated still always
runs in the main thread, but you may call get() from any thread.

Author: James Hagborg

src/main/java/org/usfirst/frc/team69/util/PeriodicScheduler.java

@@ -19,7 +19,8 @@ public class PeriodicScheduler {
     private static PeriodicScheduler theInstance;
 
     /**
-     * Return the single instance of {@link PeriodicScheduler}
+     * Return the single instance of {@link PeriodicScheduler}.  It is safe to
+     * call this method from any thread.
      * 
      * @return The sinlge instance of {@link PeriodicScheduler}
      */
@@ -40,6 +41,9 @@ private PeriodicScheduler() {
      * time {@link #run()} is called.  If using {@link HYPERRobot}, this
      * happens once every autonomousPeriodic, teleopPeriodic, and disabledPeriodic.
      * 
+     * As of hyperLib 0.3.1, it is safe to call this from within an event,
+     * and to call it from any thread.
+     * 
      * @param event A {@link Runnable} object representing the task to run 
      */
     public synchronized void addEvent(Runnable event) {
@@ -51,8 +55,10 @@ public synchronized void addEvent(Runnable event) {
      * are using {@link HYPERRobot}, you do not need to call this manually.
      */
     public synchronized void run() {
-        for (Runnable event : events) {
-            event.run();
+        /* If we use an iterator, then callind addEvent from an event itself
+         * will cause a ConcurrentModificationException */
+        for (int i = 0; i < events.size(); i++) {
+            events.get(i).run();
         }
     }
 }

src/main/java/org/usfirst/frc/team69/util/pref/BooleanPreference.java

@@ -10,7 +10,7 @@
  */
 public class BooleanPreference extends Preference {
     private boolean m_lastValue;
-    private boolean m_default;
+    private final boolean m_default;
 
     /**
      * Create a {@link BooleanPreference} object tracking the preference with
@@ -30,7 +30,7 @@ public BooleanPreference(String name, boolean value) {
      * {@inheritDoc}
      */
     @Override
-    public boolean hasChanged() {
+    public synchronized boolean hasChanged() {
         boolean newValue = get();
         boolean changed = newValue != m_lastValue;
         m_lastValue = newValue;

src/main/java/org/usfirst/frc/team69/util/pref/DoublePreference.java

@@ -10,7 +10,7 @@
  */
 public class DoublePreference extends Preference {
     private double m_lastValue;
-    private double m_default;
+    private final double m_default;
 
     /**
      * Create a {@link DoublePreference} object tracking the preference with
@@ -30,7 +30,7 @@ public DoublePreference(String name, double value) {
      * {@inheritDoc}
      */
     @Override
-    public boolean hasChanged() {
+    public synchronized boolean hasChanged() {
         double newValue = get();
         boolean changed = newValue != m_lastValue;
         m_lastValue = newValue;

src/main/java/org/usfirst/frc/team69/util/pref/IntPreference.java

@@ -3,14 +3,14 @@
 import edu.wpi.first.wpilibj.Preferences;
 
 /**
- * A class which represents an ineger-valued preference
+ * A class which represents an integer-valued preference
  * 
  * @author James Hagborg
  *
  */
 public class IntPreference extends Preference {
     private int m_lastValue;
-    private int m_default;
+    private final int m_default;
 
     /**
      * Create a {@link IntPreference} object tracking the preference with
@@ -30,7 +30,7 @@ public IntPreference(String name, int value) {
      * {@inheritDoc}
      */
     @Override
-    public boolean hasChanged() {
+    public synchronized boolean hasChanged() {
         int newValue = get();
         boolean changed = newValue != m_lastValue;
         m_lastValue = newValue;

src/main/java/org/usfirst/frc/team69/util/pref/Preference.java

@@ -45,10 +45,10 @@ public String getName() {
 
     /**
      * Check if a preference with the same name as this one already exists
-     * in the preferences fil.  If not, then create the preference using
+     * in the preferences file.  If not, then create the preference using
      * the default value.
      */
-    public void putDefaultIfEmpty() {
+    public synchronized void putDefaultIfEmpty() {
         if (!Preferences.getInstance().containsKey(m_name)) {
             putDefaultValue();
         }

src/main/java/org/usfirst/frc/team69/util/pref/PreferencesSet.java

@@ -13,6 +13,9 @@
  * Example use-cases are subsystems, PID controllers, and specific tasks like
  * vision and driving, which may have many related preferences.
  * 
+ * It is safe to share this object, as well as the Preference objects it
+ * creates, among multiple threads.
+ * 
  * @author James Hagborg
  *
  */
@@ -22,10 +25,10 @@ public class PreferencesSet {
     private final String m_name;
     private final PreferencesListener m_listener;
 
-    private ArrayList<Preference> m_preferences = new ArrayList<Preference>();
-    private HashSet<String> m_prefNames = new HashSet<String>();
+    private final ArrayList<Preference> m_preferences = new ArrayList<Preference>();
+    private final HashSet<String> m_prefNames = new HashSet<String>();
 
-    private static HashSet<String> setNames = new HashSet<String>();
+    private static final HashSet<String> setNames = new HashSet<String>();
 
     /**
      * Check the set name does not exist and add it if it does.  This needs to
@@ -82,7 +85,7 @@ public String getName() {
         return m_name;
     }
 
-    private void checkForUpdates() {
+    private synchronized void checkForUpdates() {
         boolean hasChanged = false;
 
         for (Preference pref : m_preferences) {

src/main/java/org/usfirst/frc/team69/util/pref/StringPreference.java

@@ -10,7 +10,7 @@
  */
 public class StringPreference extends Preference {
     private String m_lastValue;
-    private String m_default;
+    private final String m_default;
 
     /**
      * Create a {@link StringPreference} object tracking the preference with
@@ -35,7 +35,7 @@ public StringPreference(String name, String value) {
      * {@inheritDoc}
      */
     @Override
-    public boolean hasChanged() {
+    public synchronized boolean hasChanged() {
         String newValue = get();
         boolean changed = !newValue.equals(m_lastValue);
         m_lastValue = newValue;