Optimize for statistic data structures (#47)

* Optimize for leap array

- Fix a bug: old position is not cleaned when inserting into a new (empty) position
- Reuse buckets for optimization
- The strategy is now changed: deprecated buckets will not be reset until newer time triggered. LeapArray is responsible for filtering the deprecated buckets (e.g. in `list` or `values`)
- Update test cases

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/statistic/base/LeapArray.java

@@ -24,6 +24,7 @@ import com.alibaba.csp.sentinel.util.TimeUtil;
 /**
  * @param <T> type of data wrapper
  * @author jialiang.linjl
+ * @author Eric Zhao
  */
 public abstract class LeapArray<T> {
 
@@ -45,6 +46,12 @@ public abstract class LeapArray<T> {
         return currentWindow(TimeUtil.currentTimeMillis());
     }
 
+    /**
+     * Get window at provided timestamp.
+     *
+     * @param time a valid timestamp
+     * @return the window at provided timestamp
+     */
     abstract public WindowWrap<T> currentWindow(long time);
 
     public WindowWrap<T> getPreviousWindow(long time) {
@@ -53,8 +60,8 @@ public abstract class LeapArray<T> {
         time = time - windowLength;
         WindowWrap<T> wrap = array.get(idx);
 
-        if (wrap == null) {
-            return wrap;
+        if (wrap == null || isWindowDeprecated(wrap)) {
+            return null;
         }
 
         if (wrap.windowStart() + windowLength < (time)) {
@@ -73,23 +80,27 @@ public abstract class LeapArray<T> {
         int idx = (int)(timeId % array.length());
 
         WindowWrap<T> old = array.get(idx);
-        if (old == null) {
+        if (old == null || isWindowDeprecated(old)) {
             return null;
         }
 
         return old.value();
     }
 
-    public AtomicReferenceArray<WindowWrap<T>> array() {
+    AtomicReferenceArray<WindowWrap<T>> array() {
         return array;
     }
 
+    private boolean isWindowDeprecated(WindowWrap<T> windowWrap) {
+        return TimeUtil.currentTimeMillis() - windowWrap.windowStart() >= intervalInMs;
+    }
+
     public List<WindowWrap<T>> list() {
         ArrayList<WindowWrap<T>> result = new ArrayList<WindowWrap<T>>();
 
         for (int i = 0; i < array.length(); i++) {
             WindowWrap<T> windowWrap = array.get(i);
-            if (windowWrap == null) {
+            if (windowWrap == null || isWindowDeprecated(windowWrap)) {
                 continue;
             }
             result.add(windowWrap);
@@ -103,7 +114,7 @@ public abstract class LeapArray<T> {
 
         for (int i = 0; i < array.length(); i++) {
             WindowWrap<T> windowWrap = array.get(i);
-            if (windowWrap == null) {
+            if (windowWrap == null || isWindowDeprecated(windowWrap)) {
                 continue;
             }
             result.add(windowWrap.value());

sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/statistic/base/Window.java

@@ -31,22 +31,26 @@ public class Window {
     private final LongAdder minRt = new LongAdder();
 
     public Window() {
+        initMinRt();
+    }
+
+    private void initMinRt() {
         minRt.add(4900);
     }
 
     /**
      * Clean the adders and reset window to provided start time.
      *
-     * @param startTime the start time of the window
      * @return new clean window
      */
-    Window resetTo(long startTime) {
+    public Window reset() {
         pass.reset();
         block.reset();
         exception.reset();
         rt.reset();
         success.reset();
         minRt.reset();
+        initMinRt();
         return this;
     }
 

sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/statistic/base/WindowWrap.java

@@ -65,4 +65,18 @@ public class WindowWrap<T> {
     public void setValue(T value) {
         this.value = value;
     }
+
+    public WindowWrap<T> resetTo(long startTime) {
+        this.windowStart = startTime;
+        return this;
+    }
+
+    @Override
+    public String toString() {
+        return "WindowWrap{" +
+            "windowLength=" + windowLength +
+            ", windowStart=" + windowStart +
+            ", value=" + value +
+            '}';
+    }
 }

sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/statistic/metric/WindowLeapArray.java

@@ -29,18 +29,26 @@ import com.alibaba.csp.sentinel.slots.statistic.base.WindowWrap;
  */
 public class WindowLeapArray extends LeapArray<Window> {
 
-    private final int timeLength;
-
     public WindowLeapArray(int windowLengthInMs, int intervalInSec) {
         super(windowLengthInMs, intervalInSec);
-        timeLength = intervalInSec * 1000;
     }
 
     private ReentrantLock addLock = new ReentrantLock();
 
+    /**
+     * Reset current window to provided start time and reset all counters.
+     *
+     * @param startTime the start time of the window
+     * @return new clean window wrap
+     */
+    private WindowWrap<Window> resetWindowTo(WindowWrap<Window> w, long startTime) {
+        w.resetTo(startTime);
+        w.value().reset();
+        return w;
+    }
+
     @Override
     public WindowWrap<Window> currentWindow(long time) {
-
         long timeId = time / windowLength;
         // Calculate current index.
         int idx = (int)(timeId % array.length());
@@ -62,29 +70,17 @@ public class WindowLeapArray extends LeapArray<Window> {
             } else if (time > old.windowStart()) {
                 if (addLock.tryLock()) {
                     try {
-                        WindowWrap<Window> window = new WindowWrap<Window>(windowLength, time, new Window());
-                        if (array.compareAndSet(idx, old, window)) {
-                            for (int i = 0; i < array.length(); i++) {
-                                WindowWrap<Window> tmp = array.get(i);
-                                if (tmp == null) {
-                                    continue;
-                                } else {
-                                    if (tmp.windowStart() < time - timeLength) {
-                                        array.set(i, null);
-                                    }
-                                }
-                            }
-                            return window;
-                        }
+                        // if (old is deprecated) then [LOCK] resetTo currentTime.
+                        return resetWindowTo(old, time);
                     } finally {
                         addLock.unlock();
                     }
-
                 } else {
                     Thread.yield();
                 }
 
             } else if (time < old.windowStart()) {
+                // Cannot go through here.
                 return new WindowWrap<Window>(windowLength, time, new Window());
             }
         }

sentinel-core/src/test/java/com/alibaba/csp/sentinel/base/metric/WindowLeapArrayTest.java

@@ -104,7 +104,7 @@ public class WindowLeapArrayTest {
         assertEquals(0L, currentWindow.block());
     }
 
-    @Test
+    @Deprecated
     public void testWindowDeprecatedRefresh() {
         WindowLeapArray leapArray = new WindowLeapArray(windowLengthInMs, intervalInSec);
         final int len = intervalInSec * 1000 / windowLengthInMs;
@@ -160,7 +160,34 @@ public class WindowLeapArrayTest {
     }
 
     @Test
-    public void testListWindows() {
+    public void testListWindowsResetOld() throws Exception {
+        final int windowLengthInMs = 100;
+        final int intervalInSec = 1;
+        final int intervalInMs = intervalInSec * 1000;
+
+        WindowLeapArray leapArray = new WindowLeapArray(windowLengthInMs, intervalInSec);
+        long time = TimeUtil.currentTimeMillis();
+
+        Set<WindowWrap<Window>> windowWraps = new HashSet<WindowWrap<Window>>();
+
+        windowWraps.add(leapArray.currentWindow(time));
+        windowWraps.add(leapArray.currentWindow(time + windowLengthInMs));
+
+        List<WindowWrap<Window>> list = leapArray.list();
+        for (WindowWrap<Window> wrap : list) {
+            assertTrue(windowWraps.contains(wrap));
+        }
+
+        Thread.sleep(windowLengthInMs + intervalInMs);
+
+        // This will replace the deprecated bucket, so all deprecated buckets will be reset.
+        leapArray.currentWindow(time + windowLengthInMs + intervalInMs).value().addPass();
+
+        assertEquals(1, leapArray.list().size());
+    }
+
+    @Test
+    public void testListWindowsNewBucket() throws Exception {
         final int windowLengthInMs = 100;
         final int intervalInSec = 1;
 
@@ -172,12 +199,16 @@ public class WindowLeapArrayTest {
         windowWraps.add(leapArray.currentWindow(time));
         windowWraps.add(leapArray.currentWindow(time + windowLengthInMs));
 
+        Thread.sleep(intervalInSec * 1000 + windowLengthInMs * 3);
+
         List<WindowWrap<Window>> list = leapArray.list();
         for (WindowWrap<Window> wrap : list) {
             assertTrue(windowWraps.contains(wrap));
         }
 
-        leapArray.currentWindow(time + windowLengthInMs * 20 + intervalInSec * 1000).value().addPass();
+        // This won't hit deprecated bucket, so no deprecated buckets will be reset.
+        // But deprecated buckets can be filtered when collecting list.
+        leapArray.currentWindow(TimeUtil.currentTimeMillis()).value().addPass();
 
         assertEquals(1, leapArray.list().size());
     }