Add VariableUpdaterTask.

VariableUpdaterTask updates a variable countinously.

2 files changed, 125 insertions, 0 deletions

diff --git a/same/src/main/java/com/orbekk/same/VariableUpdaterTask.java b/same/src/main/java/com/orbekk/same/VariableUpdaterTask.java
new file mode 100644
index 0000000..44f63fe
--- /dev/null
+++ b/same/src/main/java/com/orbekk/same/VariableUpdaterTask.java
@@ -0,0 +1,63 @@
+package com.orbekk.same;
+
+import java.util.concurrent.atomic.AtomicBoolean;
+
+/** Updates a variable on-demand.
+ */
+public class VariableUpdaterTask<T> extends Thread
+        implements Variable.OnChangeListener<T> {
+    private Variable<T> variable;
+    private T newValue;
+    private AtomicBoolean hasNewValue = new AtomicBoolean(false);
+    private AtomicBoolean isReady = new AtomicBoolean(true);
+    
+    public VariableUpdaterTask(Variable<T> variable) {
+        this.variable = variable;
+    }
+    
+    public synchronized void set(T newValue) {
+        this.newValue = newValue;
+        hasNewValue.set(true);
+        notifyAll();
+    }
+    
+    /** Update the variable once. */
+    public void performWork() {
+        boolean shouldDoWork = false;
+        synchronized(this) {
+            shouldDoWork = hasNewValue.get() && isReady.get();
+            hasNewValue.set(false);
+            isReady.set(false);
+        }
+        if (shouldDoWork) {
+            variable.set(newValue);
+        }
+    }
+    
+    private synchronized void waitFor(AtomicBoolean v) {
+        while(!v.get()) {
+            try {
+                wait();
+            } catch (InterruptedException e) {
+                return;
+            }
+        }
+    }
+    
+    public void run() {
+        while (true) {
+            waitFor(isReady);
+            waitFor(hasNewValue);
+            if (Thread.interrupted()) {
+                break;
+            }
+            performWork();
+        }
+    }
+
+    @Override
+    public synchronized void valueChanged(Variable<T> unused) {
+        isReady.set(true);
+        notifyAll();
+    }
+}
\ No newline at end of file
diff --git a/same/src/test/java/com/orbekk/same/VariableUpdaterTaskTest.java b/same/src/test/java/com/orbekk/same/VariableUpdaterTaskTest.java
new file mode 100644
index 0000000..3ecf444
--- /dev/null
+++ b/same/src/test/java/com/orbekk/same/VariableUpdaterTaskTest.java
@@ -0,0 +1,62 @@
+package com.orbekk.same;
+
+import static org.junit.Assert.*;
+
+import org.junit.Before;
+import org.junit.Test;
+import static org.mockito.Mockito.*;
+
+public class VariableUpdaterTaskTest {
+    Variable<String> v;
+    VariableUpdaterTask<String> updater;
+    
+    @Before public void setUp() {
+        v = mock(Variable.class);
+        updater = new VariableUpdaterTask<String>(v);
+    }
+        
+    @Test
+    public void updatesValue() {
+        updater.set("FirstValue");
+        updater.performWork();
+        verify(v).set("FirstValue");
+    }
+
+    @Test
+    public void noUpdateIfNotSet() {
+        updater.set("FirstValue");
+        updater.performWork();
+        reset(v);
+        updater.performWork();
+        verify(v, never()).set(anyString());
+    }
+    
+    @Test
+    public void noUpdateIfNotReady() {
+        updater.set("FirstValue");
+        updater.performWork();
+        reset(v);
+        updater.set("SecondValue");
+        updater.performWork();
+        verify(v, never()).set(anyString());
+    }
+    
+    @Test
+    public void updatesWhenReady() {
+        updater.set("Value1");
+        updater.performWork();
+        reset(v);
+        updater.valueChanged(null);
+        updater.set("Value2");
+        updater.performWork();
+        verify(v).set("Value2");
+    }
+    
+    @Test
+    public void choosesLastUpdate() {
+        updater.set("FirstValue");
+        updater.set("SecondValue");
+        updater.performWork();
+        verify(v).set("SecondValue");
+    }
+}